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Preparing high-purity iron by direct reduction-smelting separation of ultra-high-grade iron concentrate
Feng Li, Man-sheng Chu, Jue Tang, Zhen-ggen Liu, Jia-xin Wang, and Sheng-kang Li
Accepted Manuscript Available online  17 February 2020, https://doi.org/10.1007/s12613-019-1959-6
[Abstract](7) [PDF 865KB](1)
Abstract:
In this study, a new process for preparing high-purity iron (HPI) is proposed and investigated by laboratory experiments and pilot tests. The results show that under conditions of a reduced temperature of 1075℃, reduced time of 5h, and CaO content of 2.5%, a DRI with a metallization rate of 96.5% was obtained through coal-based direct reduction of ultra-high-grade iron concentrate. Then, an HPI with a Fe purity of 99.95% and C, Si, Mn, and P contents as low as 8ppm, 6ppm, 14ppm and 15ppm, respectively, was prepared by smelting separation of the DRI using a smelting temperature of 1625℃, smelting time of 45 min, and CaO content of 9.3%. The product of the pilot test with a scale of 0.01 Mt/a had a lower impurity content than the Chinese industry standard. An HPI with a Fe purity of 99.97% can be produced through the direct reduction-smelting separation of ultra-high-grade iron concentrate at relatively low cost. The proposed process shows a promising prospect for application in the future.
Ultrasonic vibration assisted tungsten inert gas welding of dissimilar metals 316L and L415
Bin Wang, Hong-xia Lan, and Sen-feng Zhang
Accepted Manuscript Available online  14 February 2020, https://doi.org/10.1007/s12613-019-1960-0
[Abstract](12) [PDF 3923KB](0)
Abstract:
Ultrasonic vibration assisted tungsten inert gas welding was applied to joining stainless steel 316L and low alloy high strength steel L415. The effect of ultrasonic vibration on the microstructure and mechanical properties of a dissimilar metal welded joint of 316L and L415 was systematically investigated. The microstructure of both heat affected zones of L415 and weld metal was substantially refined and the clusters of δ ferrite appeared in traditional tungsten inert gas (TIG) weld was changed to a dispersive distribution via the ultrasonic vibration. The ultrasonic vibration promoted the uniform distribution of elements and decreased the micro-segregation tendency in the weld. With the application of ultrasonic vibration, the average tensile strength and elongation of the joint was improved from 613MPa to 650MPa and from 16.15% to 31.54%, respectively. The content of Σ3 grain boundaries around the fusion line zone is higher and the distribution is more uniform in the ultrasonic vibration assisted welded joint compared with the traditional one, indicating an excellent weld metal crack resistance.
High-temperature oxidation behavior of 9Cr-5Si-3Al ferritic heat-resistant steel
Jun-jun Yan, Xue-fei Huang, and Wei-gang Huang
Accepted Manuscript Available online  14 February 2020, https://doi.org/10.1007/s12613-019-1961-z
[Abstract](13) [PDF 2651KB](0)
Abstract:
To improve the oxidation properties of ferritic heat-resistant steels, in this study, we designed an Al-bearing Fe-9Cr-5Si-3Al ferritic heat-resistant steel. We then conducted cyclic oxidation tests to investigate the high-temperature oxidation behavior of Fe-9Cr-5Si and Fe-9Cr-5Si-3Al ferritic heat-resistant steels at 900℃ and 1000℃. The characteristics of the oxide layer were analyzed by X-ray diffraction, scanning electron microscopy, and energy dispersive spectroscopy. The results show that the oxidation-kinetics curves of the two tested steels follow the parabolic law, with the parabolic rate constant Kp of Fe-9Cr-5Si-3Al steel being much lower than that of 9Cr-5Si steel at both 900℃ and 1000℃. The oxide film on the surface of the 9Cr-5Si alloy exhibits Cr2MnO4 and Cr2O3 phases in the inner layer after oxidation at 900℃ and 1000℃. However, at oxidation temperatures of 900℃ and 1000℃, the oxide film of the 9Cr-5Si-3Al alloy consists only of Al2O3 and its oxide layer is thinner than that of the 9Cr-5Si alloy. These results indicate that the addition of Al to Fe-9Cr-5Si steel can improve its high-temperature oxidation resistance, which can be attributed to the formation of a continuous and compact Al2O3 film on the surface of the steel.
Metal-doped (Cu,Zn)Fe2O4 from integral utilization of toxic Zn-containing electric arc furnace dust: an environment-friendly heterogeneous Fenton-like catalyst
Jun-wu Li, Xing Han, Rong-xia Chai, Fang-qin Cheng, Mei Zhang, and and Min Guo
Accepted Manuscript Available online  14 February 2020, https://doi.org/10.1007/s12613-019-1962-y
[Abstract](12) [PDF 1162KB](0)
Abstract:
Pure metal-doped (Cu,Zn)Fe2O4 was first synthesized from Zn-containing electric arc furnace dust (EAFD) by solid-state reaction using copper salt as additive. The effects of the mass ratio of pretreated EAFD-to Cu2(OH)2CO3·6H2O, reaction time, and reaction temperature on the structure and catalytic ability were systematically studied. Under the optimum conditions, the decolorization, and TOC removal efficiencies of the as-prepared ferrite for treating a Rhodamine B solution were approximately 90.0% and 45.0%, respectively, and the decolorization efficiency remained 83.0% after five recycles, suggesting that the as-prepared (Cu,Zn)Fe2O4 was an efficient heterogeneous Fenton-like catalyst with high stability. The high catalytic activity mainly depended on the synergistic effect of iron and copper ions occupying octahedral positions. More importantly, the toxicity characteristic leaching procedure (TCLP) analysis illustrated that the toxic Zn-containing EAFD was transformed into harmless (Cu,Zn)Fe2O4 andthat the concentrations of toxic ions in the degraded solution were all lower than the national emission standard (GB/31574-2015), further confirming that the as obtained sample is an environment-friendly heterogeneous Fenton-like catalyst.
Curing time effect on mesocosmic parameters of cemented paste backfill through particle flow code technique
Lang Liu, Jie Xin, Chao Huan, Yujiao Zhao, Xiang Fan, Lijie Guo, and KI-IL Song
Accepted Manuscript Available online  11 February 2020, https://doi.org/10.1007/s12613-020-2007-2
[Abstract](60) [PDF 2163KB](4)
Abstract:
Several special mechanical properties such as the dilatancy and compressibility of cemented paste backfilll (CPB) are controlled by the internal microstructure and its evolution. To explore the mesocosmic structure changes of CPB during the development process. Based on the scanning electron microscopy (SEM) and mechanical test results of CPB, the particle size information of CPB was extracted, and a two-dimensional (2D) particle flow code (PFC) model of CPB was established to study the evolution rule of mesoscopic parameters during CPB development. The FISH language of the PFC was used to develop a program for establishing a PFC model according to SEM results. The mesoscopic parameters of CPB samples at different curing times, such as the coordination number (Cn), contact force chain, and rose diagram were obtained by recording and loading; these were used to analyze the intrinsic relationship between mesoscopic parameter variations and macroscopic mechanical response during CPB development. It is of great significance to establish the physical model of CPB by using PFC to reveal the mesoscopic structure of CPB.
Optimization of the heat treatment of additively manufactured Ni-base superalloy IN718
Benedikt Diepold, Nora Vorlaufe, Steffen Neumeier, Thomas Gartner, and Mathias Göken
Accepted Manuscript Available online  11 February 2020, https://doi.org/10.1007/s12613-020-1991-6
[Abstract](13) [PDF 1978KB](1)
Abstract:
Additive manufacturing (AM) of Ni-base superalloy components can lead to a significant reduction of weight in aerospace applications. AM processing of IN718 by selective laser melting results into a very fine dendritic microstructure with a high dislocation density caused by the fast solidification process. The complex phase composition of this alloy, with three different types of precipitates and high residual stresses, makes an adjustment of the conventionally used heat treatment for additively manufactured parts necessary. After a solution heat treatment, the Nb-rich Laves phase dissolved and the dislocation density is reduced, which leads to a vanishing of the dendritic substructure. Solution heat treatments at a temperature of 930℃ or 954℃ lead to the precipitation of the δ-phase, which reduces the volume fraction of the strengthening γ'- and γ''-phases, which are formed during the subsequent two stage ageing treatment. With a higher solution heat treatment temperature of 1000℃, where no δ-phase is precipitated, higher γ' and γ'' volume fractions are achieved. This resulted in an optimum strength of all solution heat treated conditions.
Electrochemical investigation of the anode processes in LiF-NdF3 melt at low oxygen content
Chen-ming Fan, Shi-zhe Liu, Jing-jiu Gu, Shi-you Guan, Jin-hua Zhao, and Bing Li
Accepted Manuscript Available online  11 February 2020, https://doi.org/10.1007/s12613-020-2010-7
[Abstract](12) [PDF 1102KB](0)
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The oxidation of oxygen ions and the generation of anode effect at low oxygen content of 150 ppm were discussed in this paper. Cyclic voltammetry and square-wave voltammetry were used to explore the anodic processes of LiF-NdF3 melt after a long period of pre-electrolysis purification at 1000℃ (oxygen content reduces from 413 ppm to 150 ppm). The oxidation process of oxygen ions can be divided into two stages:the oxidation products adsorption and CO/CO2 gas evolution stage. The adsorption stage is controlled by diffusion-controlled step, while the control process of gas evolution is electrochemical reaction step. At low oxygen content of 150 ppm, the decline amplitude of the current is much more gentle in the positive scan when anode effect occurs. The fluorine ions oxidation peaks at about 4.2 V (vs. Li/Li+) are clearly observed in the reverse scanning processes, at which the oxidation of fluorine ions and the production of perfluorocarbon occurr resulting in anode effect.
Safety of barricades in cemented paste backfill stopes
Xu Zhao, Andy Fourie, Ryan Veenstra, and Chongchong Qi
Accepted Manuscript Available online  11 February 2020, https://doi.org/10.1007/s12613-020-2006-3
[Abstract](16) [PDF 2251KB](1)
Abstract:
In underground mining, there has been increasing use of "cemented paste" for backfilling of stopes. As this cemented paste backfill (CPB) enters the stope as a fluid, shotcrete barricades are often used to retain the fill material during and after the filling operations. However, failures of barricades have been reported around the world in recent years. This paper presents an analytical solution based on elastic thin plate theory for calibrating the design of shotcrete barricades in underground mines using CPB. This solution was used to determine the quantitative relationships between lateral loading from paste and the response of the barricade during the backfilling process. The results show that the proposed solution agrees well with in situ data. According to the actual responses of barricades, the acceptable tensile stress and analysis of cracks development are proposed. The proposed solution has practical significance for underground mines.
Material flow behavior and microstructure evolution during refill friction stir spot welding of alclad 2A12-T4 aluminum alloy
Gao-hui Li, Li Zhou, Ling-yun Luo, Xi-ming Wu, and Ning Guo
Accepted Manuscript Available online  11 February 2020, https://doi.org/10.1007/s12613-020-1998-z
[Abstract](14) [PDF 3048KB](0)
Abstract:
Material flow and microstructure evolution during refill friction stir spot welding of alclad 2A12-T4 aluminium alloy are experimentally investigated using the stop-action technique. There are two material flow components, i.e., the inward or outward-directed spiral flow on the horizontal plane and the upward or downward-directed flow on the vertical plane. In the plunge stage, the flowing of plasticized metal into the cavity is similar to a stack where the upper layer is pushed by the lower layer. While in the refill stage, such a process reverses. Therefore, the vertical plasticized metal flow between adjacent layers is unobvious. The welding leads to coarsening of S in the thermo-mechanically affected zone and diminishing of S in the stir zone. Continuous dynamic recrystallization causes formation of fine equiaxed grains in the stir zone, while this process occurs more difficult in the thermo-mechanically affected zone due to the lower magnitude of deformation rate and the pinning action of S precipitates on the dislocations and sub-grain boundaries, leading to high low-angle grain boundaries fraction in this zone.
On the Cell Morphology, Porosity, Microstructure, and Mechanical Properties of Porous Fe-C-P Alloys
Hamid Sazegaran and Seyyed Mohsen Moosavi Nejad
Accepted Manuscript Available online  11 February 2020, https://doi.org/10.1007/s12613-020-1995-2
[Abstract](11) [PDF 3832KB](0)
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In the present study, open cell steel foams were successfully fabricated through powder metallurgy route using urea granules as water leachable space holder. The influence of different amounts of phosphorus (0, 0.5, 1, 2, and 4 wt.%) was investigated on the cell morphology, porosity percentage, microstructure of cell walls, and mechanical properties of steel foams. The cell morphology and microstructure of cell walls were evaluated using an optical microscope (OM) equipped with image processing software and a scanning electron microscope (SEM) equipped with energy dispersive X-ray spectroscopy (EDS). In addition, the compression tests were conducted on the steel foams using a universal testing machine. Based on microscopic images, porosities consist of spherical cells and irregularly shaped pores which are distributed in the cell walls. Results indicated that by increasing the phosphorus content, porosity percentage increases from 71.9 to 83.2 percent. The partially distributed ferrite and fine pearlite was observed in the microstructure of cell walls and α-Fe and Fe3P eutectic extended between the boundaries of agglomerated iron particles. Furthermore, elastic and long saw-toothed plateau regions was observed before fracture in the compressional stress-strain curves. According to the results, by increasing the phosphorus content from 0 to 4 wt.%, the plateau region of the stress-strain curves shifts to the right and upward. Therefore, increasing phosphorus content causes improvement in the mechanical properties of steel foams.
Microstructure and mechanical properties of friction welded carbon steel (EN24) and nickel based superalloy (IN718)
V. T. Gaikwad, M. K. Mishra, V. D. Hiwarkar, and R. K. P. Singh
Accepted Manuscript Available online  11 February 2020, https://doi.org/10.1007/s12613-020-2008-1
[Abstract](11) [PDF 2103KB](2)
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In this study, continuous drive rotary friction welding (FW) is performed to join cylindrical specimen of carbon steel (EN24) and nickel based superalloy (IN718). The microstructures of three distinguish weld zones such as weld interface (WI)/thermo mechanically affected zone (TMAZ), heat affected zone (HAZ), and base metals were examined. The joint was observed to be free from defects with uneven flash formation. Electron Back Scattered Diffraction (EBSD) analysis shows substantial changes in high angle grain boundaries, low angle grain boundaries and twin boundaries in TMAZ and HAZ areas. Also significant refinement in grain size (2-5μm) was observed at WI/TMAZ with reference to base metals. The possible causes of these are discussed. The microhardness profile across welded joint shows variation in hardness. The changes in hardness were ascribed to grain refinement, phase transformation, and dissolution of strengthening precipitates. The tensile test results reveal that joint efficiency as much as 100% can be achievable by this method.
Adsorption of Ag on M-doped graphene: first principle calculations
Min Hu, Zhou Fan, Jianyi Liu, Kun Zhang, Yang Wang, and Chunfeng Yang
Accepted Manuscript Available online  11 February 2020, https://doi.org/10.1007/s12613-020-1989-0
[Abstract](11) [PDF 983KB](0)
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Graphene is an ideal reinforcing phase for high-performance composite filler, which is of great theoretical and practical significance for improving the wettability and reliability of filler. However, the poor adsorption characteristic between graphene and silver base filler seriously affects the application of graphene-filler in the brazing field. It is a great challenge to improve the adsorption characteristic between graphene and silver base filler. To solve this issue, we studied the adsorption characteristic between graphene and silver with first principle calculation. The effects of Ga, Mo, and W on the adsorption properties of graphene were explored furtherly. There are three possible adsorbed sites, including the hollow site (H); the bridge site (B) and the top site (T). Our research found that the top site is the most preferentially adsorbed site for Ag atom, and there is a strong interaction between graphene and Ag atom due to the doped of metal elements. The doped of metal elements enhances local hybridization between C or metal atoms and Ag. Furthermore, compared with other doped structures (Ga and Mo), W atom doped is not only the most stable adsorption structure but also can improve the effectively adsorption characteristic performance between graphene and Ag.
Microwave-Assisted Reduction Roasting-Magnetic Separation Studies of Two Mineralogically Different Low-Grade Iron ores
Subhnit K. Roy, Deepak Nayak, Nilima Dash, Nikhil Dhawan, and Swagat S. Rath
Accepted Manuscript Available online  11 February 2020, https://doi.org/10.1007/s12613-020-1992-5
[Abstract](10) [PDF 4031KB](1)
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Microwave-assisted reduction behaviours of two low-grade iron ores having a similar Fe content of 49% but distinctly different mineralogical and liberation characteristics have been studied. Their performances in terms of the iron grade and recovery as obtained from the statistically designed microwave (MW) roasting followed by Low-intensity Magnetic Separation (LIMS) experiments have been compared. At respective optimum conditions, the titano-magnetite ore (O1) could yield an iron concentrate having a grade of 62.57% Fe with a Fe recovery of 60.01% while the goethitic ore (O2) could be upgraded to 64.4% Fe at a Fe recovery of 33.3%. Compared to the goethitic ore, the titano-magnetite ore responds better to MW heating. The characterization studies of the feed and roasted products obtained at different power and time using X-ray diffraction, optical microscopy, vibrating sample magnetometer and electron probe microanalysis explain the sequential reduction of the iron oxide phases. Finally, taking advantage of the MW absorbing character of the titano-magnetite ore, a blend of the same with the goethite-rich ore at a weight ratio of 60:40 (O2:O1) has been subjected to MW roasting resulting in a concentrate of 61.57% Fe with a Fe recovery of 64.47%.
Simulation on scrap melting behavior and carbon diffusion under natural convection
Ming Gao, Jin-tao Gao, Yan-ling Zhang, and Shu-feng Yang
Accepted Manuscript Available online  11 February 2020, https://doi.org/10.1007/s12613-020-1997-0
[Abstract](11) [PDF 2047KB](0)
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A 3-D model applying the temperature and carbon concentration-dependent material properties was developed to describe the scrap melting behavior and carbon diffusion under natural convection. The simulated results agreed reasonably well with the experimental ones. The scrap melting was subdivided into four stages of "① formation of a solidified layer; ② rapid melting of the solidified layer; ③ carburization; and ④ carburization + normal melting". The carburization stage could not be ignored at low temperatures as the carburization time for the sample investigated was 214 s at 1573K compared to 12 s at 1723K. The thickness of the boundary layer with significant concentration difference at 1573K increased from 130 μm at 5 s to 140 μm at 60 s. The maximum velocity caused by natural convection decreased from 0.029 m·s-1 at 5 s to 0.009 m·s-1 at 634 s because the differences in temperature and density between the molten metal and scrap decreased with time.
Graphene Nanoplatelets Reinforced 7075 Aluminum Alloy Composite Fabricated by Spark Plasma Sintering
Hui-min Xia, Lan Zhang, Yong-chao Zhu, Na Li, Yu-qi Sun, Ji-dong Zhang, and Hui-zhong Ma
Accepted Manuscript Available online  11 February 2020, https://doi.org/10.1007/s12613-020-2009-0
[Abstract](13) [PDF 700KB](0)
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0.3wt% Graphene nanoplatelets (GNPs) reinforced 7075 aluminum alloy matrix composite was consolidated by spark plasma sintering (SPS). The strength and wear resistance of the composite were investigated. The microstructures of the internal structure, the friction surface and the wear debris were characterized by Scanning Electron Microscopy (SEM), X-ray diffraction and Raman spectrum. The present results reveal that the hardness and elastic modulus of the composite are increased by 29% and 36%, respectively, compared with the original 7075 aluminum alloy. The results of the tribological experiments illustrated that the composite exhibits a lower wear rate than the original 7075 aluminum alloy.
Effects of Operation Parameters on Flow Field in Slab Continuous Casting Mold with Narrow Width
Tao Zhang, Jian Yang, Gang-jun Xu, Hong-jun Liu, Jun-jun Zhou, and Wei Qin
Accepted Manuscript Available online  11 February 2020, https://doi.org/10.1007/s12613-020-1988-1
[Abstract](8) [PDF 5292KB](0)
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The computational simulation and the high temperature measurement of velocities near the mold surface based on the rod deflection method are carried out to study the effects of operation parameters on the flow field in the slab continuous casting mold with narrow width for the production of automobile exposed panels. Reasonable agreement between the calculated results and the measured subsurface velocities of liquid steel is obtained under the different operation parameters of continuous casting process. Based on the simulated results, the flow field on the horizontal plane of 50 mm away from the meniscus can be used as the characteristic flow field for optimizing the flow field of molten steel in the mold. The increased casting speed can increase the subsurface velocity of molten steel and shift down the position of vortex core in the downward circulation zone. The flow field of liquid steel can be improved by a relatively larger Ar gas flow rate of 7 l·min-1 in the slab CC mold with 1040 mm narrow width and 1.7 m·min-1 casting speed. The Double-Roll-Flow (DRF) pattern tends to be stabilized with the 170 mm immersion depth of SEN under the present experimental conditions.
Influence of Multi-stage Heat Treatment on Microstructure and Mechanical Properties of TC21 Titanium Alloy
Wei Long, Song Zhang, Yi-long Liang, and Mei-gui Ou
Accepted Manuscript Available online  11 February 2020, https://doi.org/10.1007/s12613-020-1996-1
[Abstract](12) [PDF 1979KB](0)
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The duplex structure TC21 alloy samples were firstly solution-treated at high temperature in α+β region (940℃) (furnace cooling (FC), air cooling (AC), water cooling (WC)), followed by second-stage solution treatment at low-temperature in α+β region (900℃) and then aged at 590℃. The effect of α phase morphology and quantity on the structure and properties of TC21 alloy after different heat treatments was analyzed. In-situ tensile deformation process and crack propagation behavior were observed by scanning electron microscopy (SEM). The results show that the quantity of equiaxed α phase and the thickness of lamellar α phase reduce, and the strength and the ductility decrease with the cooling rates increase after the first-stage solution treatment. The number and the size of lamellar α phase increase after the second-stage solution due to sufficient diffusion of the alloy elements, leading to the increase of tensile strength. The amount of dispersed α phase increase after three-stage aging treatment owing to the increase of nucleation rate, resulting in the noteworthy strengthening effect. The FC sample presents better mechanical properties, because it contains more equiaxed α phases and βtrans phases than AC and WC samples after three-stage aging treatment.
Enhanced Cavitation Erosion Resistance of Friction-Stir Processed High Entropy Alloy
Rakesh. B. Nair, H. S. Arora, and H. S. Grewal
Accepted Manuscript Available online  11 February 2020, https://doi.org/10.1007/s12613-020-2000-9
[Abstract](11) [PDF 1709KB](0)
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In the present work, friction stir processing of Al0.1CoCrFeNi high entropy alloy (HEA) was performed at controlled cooling conditions (ambient and liquid submerged). Microstructural and mechanical characterization of the processed and unprocessed HEAs was evaluated using electron-back scattering diffraction (EBSD) and micro and nanoindentation. HEA under submerged cooling condition showed elongated grains (10 μm) with fine equiaxed grains (2 μm) along the boundary compared to the coarser grain size (□2 mm) of as-cast-HEA. Hardness showed remarkable improvement with four times (submerged cooling condition) and three times (ambient cooling condition) improvement than as-cast HEA (□150 HV). Enhanced hardness is attributed to significant grain refinement for processed HEAs. Cavitation erosion was behavior of all the samples was evaluated using ultra sonication method. All the HEAs showed better cavitation erosion resistance than the stainless steel. The sample processed under submerged liquid condition showed around 20 and 2 times highest erosion resistance than SS316L and as-cast HEA, respectively. The enhanced erosion resistance of the processed HEA is related to their increased hardness, resistance to plasticity and better yield strength compared to the as-cast-HEA. Surface examination of the tested samples showed nucleation and growth of pits, and plastic deformation of material followed by fatigue-controlled disintegration are the primary material removal mechanism.
Investigation of structural, morphological, and electrochemical properties of mesoporous La2CuCoO6 rods fabricated by facile hydrothermal route
Jashandeep Singh and Ashok Kumar
Accepted Manuscript Available online  11 February 2020, https://doi.org/10.1007/s12613-020-2011-6
[Abstract](10) [PDF 1306KB](0)
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This work reveals facile hydrothermal synthesis of double perovskite La2CuCoO6. The X-ray diffraction pattern confirmed the formation of monoclinic phase with P121/c1 symmetry. The transmission electron microscope revealed that the self-assembled porous rods were composed of the nanocrystallites aggregates. The estimated value of specific surface area of mesoporous rods with average pore diameter of ~6 nm was ~41m2/g. The presence of ions with oxidation states as La3+, Cu2+ and Co2+/Co3+ has been confirmed on the surface of mesoporous La2CuCoO6 rods via X-ray photoelectron spectroscopic analysis. The fabricated electrode of mesoporous La2CuCoO6 rods exhibited pseudocapacitive behavior via cyclicvoltammetry and chronopotentiometry with observed value of specific-capacitance of 259.4 F/g at current-density of 0.5 A/g. A retention of ~89% in specific capacitance has been achieved after 1000 charge/discharge cycles at constant current-density of 4 A/g.
Chlorination roasting coupled water leaching process for potash recovery from waste mica scrap using dry marble sludge powder and sodium chloride
Sandeep Kumar Jena, Jogeshwar Sahu, Geetikamayee Padhy, Swagatika Mohanty, and Ajit Dash
Accepted Manuscript Available online  11 February 2020, https://doi.org/10.1007/s12613-020-1994-3
[Abstract](9) [PDF 2445KB](0)
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The present paper reports the effective utilisation of marble sludge powder (MSP) for the recovery of potash values from waste mica scrap using chlorination roast-leaching method. Characterisation studies indicate the presence of dolomite as major mineral phase in MSP, whereas it is muscovite and quartz in mica sample. The acid leaching studies suggest a maximum of 22% potash recovery under conditions like 4M H2SO4 acid, particle size 100μm, stirring speed 600rpm, leaching temperature 75℃ and time 90 min. In order to achieve a lowest-level of 80-90% potash recovery, the chlorination roasting-water leaching process was adopted. The optimum conditions for recovery of ~93% of potash from mica (K2O~8.6%) requires 900℃ roasting temperature, 30 min roasting time with a ratio of Mica:MSP:NaCl 1:1:0.75.The roasting temperature and% NaCl is found to be the most important factor for the recovery process. The reaction mechanism suggests the formation of different mineral phases like sylvite (KCl), wollastonite, kyanite, enstatite during roasting, which confirmed from the XRD phases and SEM morphologies. The effectiveness of the MSP blended NaCl for potash recovery was found to be better as compared with other reported commercial roasting additives.
Purification of Specularite by Centrifugation Instead of Flotation to Produce Iron Oxide Red Pigment
Xi Zhang, Shun-Wei Zhu, Yu-Jiang Li, Yong-Li Li, Qiang Guo, and Tao Qi
Accepted Manuscript Available online  11 February 2020, https://doi.org/10.1007/s12613-020-2003-6
[Abstract](9) [PDF 957KB](0)
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In this study, specularite, a high gradient magnetic separation concentrate was used as raw material in reverse flotation. Iron concentrate with a grade of 65.1wt% and a recovery rate of 75.31% was obtained. The optimal rotating drum speed, feed concentration, and other conditions for the centrifugal concentrator, which served as the deep purification equipment for preparation of iron oxide red pigments, were discovered. Under optimal conditions, a high-purity iron oxide concentrate with a grade of 69.38wt% and a recovery rate of 80.89% was obtained, which can be used as a raw material for preparing iron oxide red pigment. After calcining with sulfuric acid, iron red products with different hues were obtained. Simultaneously, middling with a grade of 60.20wt% and a recovery rate of 17.51% was obtained, which can be used in blast furnace ironmaking. High value utilization of specularite beneficiation products was thus achieved.
Mechanics and safety issues in tailings-based backfill: a review
Xu Zhao, Andy Fourie, and Chong-chong Qi
Accepted Manuscript Available online  11 February 2020, https://doi.org/10.1007/s12613-020-2004-5
[Abstract](18) [PDF 1658KB](1)
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The voids (referred to as "stopes") are generally created during underground mining activities, which can lead to both local and regional geotechnical instabilities. To assist in managing the stability of mining related voids and improve recovery of orebodies, tailings-based backfill technology has been widely used around the world. In the design of tailings-based backfilling strategy, the specific function and engineering requirements of the filling are intimately dependent on the stress distribution within the backfilled stope. In this paper, main mechanics involved in tailings-based backfilling in underground mines have been reviewed, which includes arching, consolidation, hydration process and movement of surrounding rocks. Also, research about the safety of a barricade and stability of an exposed face are presented. It was concluded that the backfilling process should be performed based on a better understanding of complicated interactions of mechanisms of filling, consolidation and hydration process (when cement added).
A comparative study between friction stir processing and friction stir vibration processing to develop magnesium surface nanocomposite
Behrouz Bagheri, Mahmoud Abassi, Amin Abdollahzadeh, and Amir Hossein Kokabi
Accepted Manuscript Available online  11 February 2020, https://doi.org/10.1007/s12613-020-1993-4
[Abstract](10) [PDF 2113KB](0)
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Friction stir processing (FSP) can be used to develop a surface composite. In the current research, a modified method of FSP, entitled friction stir vibration processing (FSVP) was applied to develop a surface composite on AZ91 magnesium alloy. In this method, the workpiece is vibrated normal to processing direction. The results indicated that FSVP led to more homogenous distribution of SiC particles in the microstructure compared to FSP. The results also showed that matrix grains for FSV processed specimens (around 26.43±2 μm) were finer than those for FS processed specimens (around 39.43±2 μm). These led to an increase in ultimate tensile strength (UTS) from 283 MPa for FS processed specimen to 361 MPa for FSV processed specimen and hardness increase from 105 Hv for the former specimen to 128 Hv for the latter one. The higher plastic strain in the material during FSVP, due to workpiece vibration, results in higher dynamic recrystallization and correspondingly, finer grains are developed. The elongation and formability index of FS processed specimen increased from 12.8% and 3639 MPa.% respectively to 16.9% and 6107 MPa.% for FSV processed specimen. It was also found that the effects of FSVP intensified, as vibration frequency increased.
Influence of welding speed on the formation of microstructure in friction stir welded 304 austenitic stainless steels
Mohsen Hajizadeh, Sajjad Emami, and Tohid Saeid
Accepted Manuscript Available online  11 February 2020, https://doi.org/10.1007/s12613-020-2001-8
[Abstract](9) [PDF 4436KB](0)
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Influence of welding speed on the joint microstructures of an austenitic stainless steel produced by friction stir welding (FSW) technique was investigated. The FSW process was conducted at rotational speed of 400 rpm and welding speeds of 50 and 150 mm/min. The study was conducted using electron backscattered diffraction (EBSD) technique in different regions of the resultant stir zones (SZs). The results show that the texture of the advancing side (AS) is mainly composed of C {001}<110> and cube {001}<100> texture components along with partial B/B {112}<110> component. Running from the AS towards the center and the retreating side (RS), cube texture component disappeared and the A1*/A2* {111}<112> component developed and predominated the other components. Higher welding speed greatly affected and decreased the intensity of the textures in the resultant SZs. Moreover, higher welding speed (lower heat input) resulted in lower frequency of cube texture in the AS.
Interactive effect of minerals in the flotation of complex ores: A brief review
Wan-zhong Yin and Yuan Tang
Accepted Manuscript Available online  11 February 2020, https://doi.org/10.1007/s12613-020-1999-y
[Abstract](14) [PDF 1831KB](0)
Abstract:
Froth flotation is the most effective industrial method used for the separation of fine-grained minerals. The main problem for the flotation of complex ores, obviously, is the negative effect of the interactions among minerals in slurry, which leads to the variation of surface properties in the process of separation. In this review, the studies of interactive effect among minerals in the flotation of iron ores, magnesite ores, and scheelite ores are summarized and the main problems and mechanisms that diminish the separation efficiency of minerals are revealed in detail. The recent research achievements in flotation of those ores confirmed that the mineral aggregation, coating, and dissolution, among other factors caused by interacting behavior explains the depressing effects of fine particles on minerals separation. In addition, the solvable methods for these effects were further discussed. There is good reason to believe that the novel flotation processes and more selective reagents are critical for the further investigations into various approaches to improving the beneficiation efficiency of those ores. This paper is intended to provide a good reference for studies related to the flotation of complex ores.
Factor researches on purity of magnesium titanate directly prepared from seashore
Xiao-ping Wang, Zhao-chun Li, Ti-chang Sun, Jue Kou, and Xiao-hui Li
Accepted Manuscript Available online  11 February 2020, https://doi.org/10.1007/s12613-020-1990-7
[Abstract](11) [PDF 1806KB](0)
Abstract:
With the seashore titanomagnetite concentrate as raw material and adding magnesium oxide (MgO), the external coal reduction was carried out to directly prepare magnesium titanate. The effects of roasting temperature and the types and dosage of reductants on purity of generated magnesium titanate particles were systematically investigated. SEM-EDS analyses were performed to characterize the magnesium titanate particles, observing their purity under different conditions. Results showed that the roasting temperature had a great influence on purity of magnesium titanate. At 1200, 1300, or 1400℃, part magnesium ferrite and magnesium aluminate spinel were dissolved in magnesium titanate. However, with increasing the roasting temperature to 1500℃, the relatively pure magnesium titanate particles were generated, due to that no magnesium ferrite was dissolved in them. In addition, the types and dosages of reductants also had a great effect on the purity of magnesium titanate. Using lignite as reductant and at its dosage of 70wt%, the number of the fine metallic iron disseminated in magnesium titanate particles obviously decreased, thus forming magnesium titanate particles with high purity. At roasting temperature of 1500℃ and using the 70wt% lignite as the reductant, the magnesium titanate product with yield of 30.63wt% and iron content of 3.01wt% was obtained through magnetic separation.
Risk management for mine closure: A cloud model and a hybrid semi-quantitative decision method
Chao-qun Cui, Bing Wang, Yi-xin Zhao, Yong-Jin Zhang, and Li-ming Xue
Accepted Manuscript Available online  11 February 2020, https://doi.org/10.1007/s12613-020-2002-7
[Abstract](14) [PDF 1170KB](1)
Abstract:
Mine closure is associated with many negative impacts to society and the environment. These effects would pose mine closure risks if they are not rationally treated. To mitigate these adverse impacts, a risk management method should be employed to address mine closure issues. This paper proposes an integral framework for mine closure risk management that includes risk assessment and risk treatment. Given the fuzziness and randomness contained in the transformation between qualitative and quantitative knowledge in the risk assessment process, this paper presents a novel risk assessment method based on the cloud model, which fully considers the uncertainty in risks themselves and in the reasoning process. Closed mine reutilization is an effective risk treatment option to response to the identified high risks, but it requires the selection of the optimal reutilization strategies for the successful implementation of the reuse plan. To this end, a hybrid semi-quantitative decision method is proposed to optimize decision making. The results of a case study showed that this risk management methodology can help budget planning for risk treatment and can provide an instructional framework for reducing the negative effects of closed mines effectively.
Experimental and theoretical verification of cations distribution and spin canting effect via structural and magnetic studies of Ni0.6-xZn0.4CoxFe2O4 nanoparticles
Rajinder Kumar, Dipti Rawat, P. B. Barman, and Ragini Raj Singh
Accepted Manuscript Available online  11 February 2020, https://doi.org/10.1007/s12613-020-2005-4
[Abstract](10) [PDF 1044KB](0)
Abstract:
Nanoparticles of Ni0.6-xZn0.4CoxFe2O4 were prepared by aqueous sol-gel auto-combustion route. Ni-Zn-Ferrite system was doped with Co to improve the magnetic properties for application purposes. Structural determination of the phase and crystallite size were found using X-ray diffraction technique. Spinel cubic (single-phase) nanoparticles were formed at some specific x compositions, while at other compositions partial hematite (α-Fe2O3) secondary phase was formed. The tuned values of saturation magnetization directly depend upon the concentration of hematite phase, at this point the value of magnetic saturation become smaller which causes high spin canting effect resulting in decrease in net magnetic moment of the structure. Further doping of Co2+ ions enhances the magnetic properties due to its high magnetic moment and distributions. To cross-check the experimental findings, theoretical analysis was performed using most suitable proposed cations distribution and it supports well. The observed structural and magnetic findings would contribute effectively in electromagnetic-interference-shielding and magnetic-recording-device applications.
Chloride resistance of Cr-bearing alloy steels in carbonated concrete pore solutions
Jing Ming and Jin-jie Shi
Accepted Manuscript Available online  18 January 2020, https://doi.org/10.1007/s12613-019-1920-8
[Abstract](111) [FullText HTML](1) [PDF 1232KB](10)
Abstract:
The effect of carbonation on the chloride resistance of low-carbon steel and two Cr-bearing alloy steels in simulated concrete pore solutions was investigated. The chloride threshold values of steels were determined on the basis of corrosion potential (Ecorr) and polarization resistance (Rp). Moreover, the chloride-induced corrosion behavior of steels was evaluated using electrochemical impedance spectroscopy, cyclic voltammetry, cathodic potentiodynamic polarization, and scanning electron microscopy/energy dispersive X-ray spectroscopy measurements. Alloy steels have higher chloride resistance than low-carbon steel in carbonated and non-carbonated concrete pore solutions. The chloride resistance of alloy steels improves with increasing Cr content. In addition, the chloride resistance of all steels is negatively affected by the carbonation of concrete pore solution, especially for alloy steel with high Cr content in the presence of high chloride content.
Biodegradable magnesium matrix composites: a review
Jin-long Su, Jie Teng, Zi-li Xu, and Yuan Li
Accepted Manuscript Available online  14 January 2020, https://doi.org/10.1007/s12613-020-1987-2
[Abstract](111) [PDF 997KB](18)
Abstract:
Biodegradable magnesium alloys as a new biomedical implant material have been extensively studied because of their notable biodegradability over traditional bio-inert metals. However, the excessive degradation rate of pure magnesium leads to the loss of its mechanical integrity before the tissue recovers completely. The solution to this challenge is (i) purification, (ii) alloying, (iii) surface modification and (iv) synthesizing biodegradable magnesium matrix composites (BMMCs). Owing to the tunability of mechanical properties, adjustability of degradation rate and improvement of biocompatibility, BMMCs using Mg as the matrix reinforced with bioactive reinforcements have a promising future as a new generation of biomedical implant application. In this review, the processing methods, Mg matrix and reinforcement phases of BMMCs are discussed. Moreover, the present review provides a comprehensive understanding of various BMMCs so far, with the aim to bring out the governing aspects of mechanical properties, corrosion behavior and biocompatibility achieved. Finally, this paper also comprehensively discusses the research direction and further development for these materials.
Dielectric Properties Measurement for Microwave Synthesis of Titanium Carbide with Ti-bearing Blast Furnace Slag
Peng Liu, Li-bo Zhang, Bing-guo Liu, Guang-jun He, and Jin-hui Peng
Accepted Manuscript Available online  14 January 2020, https://doi.org/10.1007/s12613-020-1985-4
[Abstract](52) [PDF 2185KB](3)
Abstract:
The preparation of functional material titanium carbide by carbothermal reduction of Ti-bearing blast furnace slag with microwave heating is an effective method for comprehensive recovery of valuable metals and alleviation of environmental pressure caused by slag stocking. High temperature heating dynamic dielectric parameters of Ti-bearing blast furnace slag/pulverized coal mixture are measured by the cylindrical resonant cavity perturbation method. Combining transient dipole and large π bond delocalization polarization phenomenon, the interaction mechanism of microwave macroscopic non-thermal effect on the synthesis reaction of titanium carbide was revealed. The thickness range of the material during microwave heating is optimized by the joint analysis of penetration depth and reflection loss, which is of great significance to the design of microwave reactor for carbothermal reduction of Ti-bearing blast furnace slag.
Effect of heat treatment on microstructure and mechanical properties of dissimilar structural steel to mild steel composite plates fabricated by explosion welding
En-ming Zhang, Yi-ming Zhao, Zhong-mou Wang, and Wen-ya Li
Accepted Manuscript Available online  14 January 2020, https://doi.org/10.1007/s12613-020-1986-3
[Abstract](73) [PDF 1259KB](2)
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In this study, dissimilar structural steel to mild steel composite plates were joined by explosion welding, which were heat treated afterwards by quenching at 840℃ for 30 min followed by tempering at 200℃ for 3 h. The microstructure was investigated under an optical microscope and a scanning electron microscope. The mechanical properties were measured using Vickers microhardness and Charpy impact tests. Results show a deformed interface with typical wave features from explosion welding at the welding zone and no defects in the weld zone. And the ferrite in the parent plate in the weld zone is elongated due to the strong plastic deformation from the explosion. After heat treatment, the hardness of the flyer plate (structural steel) is over 800 HV0.2, while the parent plate (mild steel) is 290 HV0.2 with martensite present which increased the hardness of the plates. The average impact energy was increased from 18.5 J to 44.0 J following heat treatment because of the recrystallized grains form at the weld interface due to dynamic recovery and local recrystallization, together with strong element diffusion between the two plates.
On the influence of glycine additive on the corrosion and wear performance of electroplated trivalent chromium coating
Navid Mehdipour, Milad Rezaei, and Zeynab Mahidashti
Accepted Manuscript Available online  8 January 2020, https://doi.org/10.1007/s12613-020-1975-6
[Abstract](65) [PDF 2514KB](8)
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The aim of this work was to evaluate the effect of various molar ratios of glycine to chromium salt and different current densities on the corrosion and wear behavior of Cr (III) electroplated coatings. The morphology and thickness of the coatings was investigated by scanning electron microscopy (SEM). The wear properties of the coatings was studied using pin on disk and hardness tests, while corrosion behavior of the coatings was identified using linear polarization (LP), small amplitude cyclic voltammetry (SACV) and electrochemical impedance spectroscopy (EIS) methods. By increasing the glycine concentration, a structure with low crack density was obtained. In all molar ratios, maximum thickness and current efficiency was observed in current density of 150 mA.cm-2. All the electrochemical methods gave a consistent result and a maximum corrosion resistance of approximately 14000 Ω.cm2 was obtained in the case of Gly:Cr=3:1 and current density of 200 mA.cm-2.
Electrodeposition of Functionally Graded Ni-W/Er2O3 Rare Earth Nanoparticle Composite Film
Guo-qun Lai, Hong-zhong Liu, Bang-dao Chen, Dong Niu, Biao Lei, and Wei-tao Jiang
Accepted Manuscript Available online  8 January 2020, https://doi.org/10.1007/s12613-019-1953-z
[Abstract](37) [PDF 3051KB](1)
Abstract:
Multi-layered functionally graded (FG) structure Ni-W/Er2O3 nanocomposite films were prepared by continuously changing the deposition parameters, in which the Er2O3 and W contents varied with thickness. The microstructure and chemical composition of the electrodeposited Ni-W/Er2O3 films were determined by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). The anti-corrosion and wear properties of the electrodeposition films were investigated by electrochemical measurement and ball-on-disk friction test. The microhardness distribution of the cross section of nanocomposites was measured by nanoindentation. The results showed that with decreasing agitation rate or increasing average current density, the contents of Er2O3 nanoparticles and tungsten were distributed in a gradient along the thickness, and the content on the surface was larger. By comparison, FG Ni-W/Er2O3 films had better anti-corrosion and wear properties than the uniform Ni-W/Er2O3 film. Atomic force microscopy (AFM) and profilometry measurements indicated that Er2O3 nanoparticles had an effect on the surface roughness.
Formation of Interfacial Al-Ce-Cu-W Amorphous Layers in Aluminum Matrix Composite Through Thermally Driven Solid-State Amorphization
Zheng Lv, Chang-hui Mao, Jian Wang, Qiu-shi Liang, Shu-wang Ma, and Wen-jing Wang
Accepted Manuscript Available online  8 January 2020, https://doi.org/10.1007/s12613-019-1952-0
[Abstract](55) [PDF 1903KB](1)
Abstract:
In this work, interfacial Al-Ce-Cu-W amorphous layers formed through thermally driven solid-state amorphization within the (W+CeO2)/2024Al composite were investigated. The elemental distributions and interfacial microstructures were examined with an electron probe microanalyzer and a high-resolution transmission electron microscope, respectively. The consolidation of composites consisted of two thermal processes, i.e., vacuum degassing (VD) and hot isostatic pressing (HIP). During consolidation, not only the three major elements (Al-W-Ce) but also the alloying elements (Mg-Cu) in the Al matrix contributed to amorphization. At VD and HIP temperatures of 723 and 763 K, interfacial amorphous layers were formed within the composite. Three diffusion processes are necessary for interfacial amorphization, i.e., (a) long-range diffusion of Mg from the Al matrix to the interfaces during VD, (b) long-range diffusion of Cu from the Al matrix to the interfaces during HIP, and (c) short-range diffusion of W toward the Al matrix during HIP. The newly formed interfacial Al-Ce-Cu-W amorphous layers can be categorized under the Al-Ce-TM (TM:transition metals) amorphous system.
Liquation Cracking in the Heat-Affected Zone of IN939 Superalloy Tungsten Inert Gas Weldments
H. Kazempour-Liasi, M. Tajally, and H. Abdollah-Pour
Accepted Manuscript Available online  8 January 2020, https://doi.org/10.1007/s12613-019-1954-y
[Abstract](64) [PDF 3457KB](3)
Abstract:
The main aim of this study was to investigate liquation cracking in the heat-affected zone (HAZ) of the IN939 superalloy upon tungsten inert gas welding. A solid solution and age-hardenable filler metals were further studied. On the pre-weld heat-treated samples, upon solving the secondary γ' particles in the matrix, primary γ' particles grew in the base metal to "ogdoadically diced cubes" of about 2 μm in side length. The pre-weld heat treatment reduced the hardness of the base metal to about 310 HV. Microstructural studies using optical and field-emission scanning electron microscopy revealed that the IN939 alloy was susceptible to liquation cracking in the HAZ. The constitutional melting of the secondary, eutectic, and Zr-rich phases promoted the liquation cracking in the HAZ. The microstructure of the weld fusion zones showed the presence of fine spheroidal γ' particles with a size of about 0.2 μm. The phases increased the hardness of the weld pools after the post-weld heat treatment to about 350 and 380 HV for the Hastelloy X and IN718 filler metals, respectively. Application of a suitable solid solution filler metal could partially reduce the liquation cracking in the HAZ of IN939 alloy.
Biooxidation-Thiosulfate Leaching of Refractory Gold Concentrate
He-fei Zhao, Hong-ying Yang, Lin-lin Tong, Qin Zhang, and Ye Kong
Accepted Manuscript , https://doi.org/10.1007/s12613-020-1964-9
[Abstract](78) [PDF 870KB](4)
Abstract:
A process of biooxidation followed by thiosulfate leaching of gold from refractory gold concentrate was investigated. Mineralogical studies on the concentrate showed that very fine gold grains (<10 μm) were encapsulated in pyrite and arsenopyrite, while the amount of monomer gold was only 21%. The gold-bearing sample was identified as a high-sulfur fine-sized wrapped-type refractory gold concentrate. The gold leaching efficiency obtained by direct cyanidation was only 59.86%. After biooxidation pretreatment, the sulfide minerals were almost completely decomposed, 92% of the mineral particles of the biooxidation residue were decreased to <38 μm, and the amount of monomer gold in the biooxidation residue was over 86%. Meanwhile, the gold content in the biooxidation residue was enriched to 55.60 g/t, and the S, Fe, and As contents were reduced to approximately 19.8, 6.97, and 0.13wt%, respectively. Ammoniacal thiosulfate was used for gold extraction from the biooxidation residue of the refractory gold concentrate. The results showed that the optimal reagent conditions were 0.18 M thiosulfate, 0.02 M copper(II), 1.0 M ammonia, and 0.24 M sulfite. Under these conditions, a maximum gold leaching efficiency of 85.05% was obtained.
Fabrication of phosphor bronze/Al, two phase material, through recycling phosphor bronze chips using hot extrusion process and investigation on their microstructural and mechanical properties
Majid Hosseini and Mohammad Hossein Paydar
Accepted Manuscript Available online  8 January 2020, https://doi.org/10.1007/s12613-020-1980-9
[Abstract](74) [PDF 2044KB](4)
Abstract:
Despite conventional methods of recycling chips, solid state techniques are significantly popular today, by which it is possible to recycle wasted metals directly into consolidated products with desired shape and design. In the present work, feasibility of phosphor bronze chips' recycling through hot extrusion process by using aluminum powder as metal binder for fabrication of metal fibers reinforce aluminum matrix composite is studied. Based on that, mixtures including 20 to 50 vol.% of chips were prepared, cold compacted and then extruded. Quality of the consolidated samples were evaluated by measuring the density of the fabricated composites and studying their microstructures. In addition, mechanical properties of the fabricated composites were evaluated by the means of tensile and hardness tests. Furthermore, fracture surface of the samples was analyzed to study fracture mechanism as a function of phosphor bronze chips' volume fraction in the fabricated composite. The results indicated that the most appropriate consolidation takes place for the sample including 20 vol.% of chips extruded at 465℃ and the chips perfectly act as fibers to improve mechanical properties especially UTS in comparison with the Al matrix not included chips, produced under the condition.
Mineral transition and formation mechanism of calcium aluminate compounds in CaO-Al2O3-Na2O system during high-temperature sintering
Hai-yan Yu, Xiao-lin Pan, Yong-pan Tian, and Gan-feng Tu
Accepted Manuscript Available online  8 January 2020, https://doi.org/10.1007/s12613-019-1951-1
[Abstract](64) [PDF 1408KB](3)
Abstract:
The mineral transition and formation mechanism of calcium aluminate compounds in CaO-Al2O3-Na2O system during the high-temperature sintering process were systematically investigated using DSC-TG, XRD, SEM-EDS, FTIR and Raman spectra, and the crystal structure of Na4Ca3(AlO2)10 was also simulated by Material Studio software. The results indicate that the minerals formed during the sintering process include Na4Ca3(AlO2)10, CaO·Al2O3, and 12CaO·7Al2O3, and the content of Na4Ca3(AlO2)10 can reach 92wt% when sintered at 1200℃ for 30 min. The main formation stage of Na4Ca3(AlO2)10 occurs at temperatures from 970℃ to 1100℃ and the content can reach 82wt% when the reaction temperature is increased to 1100℃. The crystal system of Na4Ca3(AlO2)10 is tetragonal, and the cells prefer to grow along crystal planes (110) and (210). The formation of Na4Ca3(AlO2)10 is an exothermic reaction that follows a secondary reaction model, and its activation energy is 223.97 kJ/mol.
Anodized Metal Oxide Nanostructures for Photoelectrochemical Water Splitting
Ying-zhi Chen, Dong-jian Jiang, Zheng-qi Gong, Jing-yuan Li, and Lu-ning Wang
Accepted Manuscript Available online  8 January 2020, https://doi.org/10.1007/s12613-020-1983-6
[Abstract](55) [PDF 1308KB](0)
Abstract:
Photoelectrochemical (PEC) water splitting offers the capability of harvesting, storing solar energy and also converting it into clean and sustainable hydrogen energy. Metal oxides are appealing photoelectrode materials in terms of their easy manufacturing and relatively high stability. In particular, metal oxides prepared by electrochemical anodization are typical of ordered nanostructures, which are more beneficial for the light harvesting, charge transfer and transport, as well as the the adsorption and desorption of the reactive species due to its high specific surface area (SSA) and the rich channels. However, the bare anodic oxides still suffer from low charge separation and sunlight absorption efficiencies. Accordingly, many strategies have been explored and investigated to modify the anodic oxides. In this review, we attempt to summarize the recent advances over the rational design and modifications of these oxides from processes before, during, and after anodization. Rational design strategies have been nicely addressed for each part with an aim to boost overall PEC performance. Finally, the ongoing efforts and challenges for future development of practical PEC electrodes are also proposed.
Deformation Behavior and Plastic Instabilities of Boronized Al0.25CoCrFeNi High-Entropy Alloys
Jinxiong Hou, Jing Fan, Huijun Yang, Zhong Wang, and Junwei Qiao
Accepted Manuscript Available online  8 January 2020, https://doi.org/10.1007/s12613-020-1967-6
[Abstract](45) [PDF 2889KB](1)
Abstract:
Using thermochemical treatments, boronized layers were successfully prepared on Al0.25CoCrFeNi high-entropy alloy (HEAs). The thickness of boronized layers range widely from 20 μm to 50 μm, depending on the heat treatment times. Astonishingly, boronizing remarkably improves the surface hardness from 188 HV to 1265 HV after treating at 900℃ for 9 h. Additionally, boronizing promotes the yield strength of HEAs from 195 MPa to 265 MPa, but deteriorates the tensile ductility. Multiple cracking in the boride layers obviously decreases the plasticity. Crucially, the insufficient work-hardening capacity essentially facilitates the plastic instability of boronized HEAs. The fracture modes gradually transform from dimples to quasi-cleavage and eventually to cleavage with decreasing the thickness of substrate.
The Effect of Large Load on the Wear and Corrosion Behavior of High-strength EH47 Hull Steel in 3.5wt%NaCl Solution with Sand
Hong-mei Zhang, Yan Li, Ling Yan, Fang-fang Ai, Yang-yang Zhu, and Zheng-yi Jiang
Accepted Manuscript Available online  8 January 2020, https://doi.org/10.1007/s12613-020-1978-3
[Abstract](58) [PDF 5491KB](2)
Abstract:
In order to simulate the wear and corrosion behavior of high-strength EH47 hull steel in a complicated marine environment in which seawater, sea ice, and sea sand coexist, the accelerated wear and corrosion tests were performed in laboratories using a tribometer. The effect of large loads on behavior of abrasion and corrosion in the 3.5wt%NaCl solution with ice and sand to simulate marine environment were investigated. The experimental results showed that the friction coefficient decreases with increased working loads, meanwhile, the loading force and sand on the disk have an greatly influence on the COF. The mechanisms of friction and the coupling effect of abrasion and corrosion in the 3.5wt%NaCl solution with sand were the wear and corrosion mechanisms, furthermore, wear mechanism had the predominant effect.
High Cr(VI) adsorption capacity of Rutile titania prepared by hydrolysis of TiCl4 with AlCl3 addition
Shun Wu, Xiao-bo He, Li-jun Wang, and Kuo-Chih Chou
Accepted Manuscript Available online  8 January 2020, https://doi.org/10.1007/s12613-020-1965-8
[Abstract](48) [PDF 1114KB](0)
Abstract:
Rutile titania has been successfully prepared via hydrolysis of TiCl4 with AlCl3 addition. The powders are characterized via X-ray powder diffraction (XRD), scanning electron microscopy (SEM), and Brunauer-Emmett-Teller (BET). In the present system, AlCl3 plays a role as a nucleating agent and induces the formation of rutile. The influences of HCl and isopropanol on the purity and morphorlogy of rutile titania are investigated. It is found that the purity of rutile titania can be improved via increasing the concentration of HCl. Rutile titania particles in spherical morphology and evenly dispersed can be obtained when HCl and isopropanol concentrations are 0.5 mol·L-l, 1 mol·L-l respectively. Furthermore, such titania powders is applied to the adsorption test of heavy metal pollutant Cr(VI). S-9 Rutile titania has greater adsorption performance and the removal efficiency closes to 100% after adsorbing 60 min when the concentration is 200 mg·L-l. The maximum adsorption capacity of on rutile titania is 28.9 mg·g-1. This work provides an easy way to prepared high performance rutile titania, which is quite promising in water pollution treatment application.
Effect of curing humidity on performance of cemented paste backfill
Di Wu, Run-kang Zhao, Chao-wu Xie, and Shuai Liu
Accepted Manuscript Available online  8 January 2020, https://doi.org/10.1007/s12613-020-1970-y
[Abstract](51) [PDF 1095KB](7)
Abstract:
Cemented paste backfill (CPB), a mixture of tailings, binder and water, is being used increasingly and extensively for ore resource recovery, ground subsidence control, and mine waste management. Once placed, the CPB is subjected to complex ambient conditions, which significantly affect the performance of CPB, such as water content, temperature and strength. Thus, a series of laboratory programs including investigation of moisture, temperature, stress-strain relation, and microstructure are conducted in this study to present the effect of curing humidity on the behaviors of CPB. The obtained results indicate that ambient humidity can dramatically affect CPB in terms of its macro performance of internal relative humidity, temperature and strength, as well as the micro expression, for example, a rise of curing humidity favors binder hydration, and then the increase of hydration products, temperature and peak stress in the CPB. The obtained results can contribute to a better understanding of the responses of CPB to different environmental conditions.
Early-age strength property improvement and stability analysis of unclassified tailings paste backfill material
Qian Zhou, Juan-hong Liu, Ai-xiang Wu, and Hong-jiang Wang
Accepted Manuscript Available online  8 January 2020, https://doi.org/10.1007/s12613-020-1977-4
[Abstract](64) [PDF 1358KB](2)
Abstract:
For the poor early compressive strength (ECS) of backfilling material which may greatly affect the mining and backfill cycle, the high-density tailings, little cementitious material and additives are used for preparing paste backfill material (PBM) with high ECS. The effects and mechanisms of different early strength agents on the property of PBM are studied. Firstly, the relatively good types and dosages of single-component additives are selected by unconfined compressive strength (UCS) test of binder powder (BP) paste without tailings. Then, parts of them are mixed for finding the best combination of multi-component. Finally, the relatively good types and dosages of single-component and multi-component additives are added to the PBM. The adaptability of additives to unclassified tailings is verified by UCS test of PBM. The action mechanism of additives on PBM property is analyzed by X-ray diffraction (XRD), scanning electron microscope (SEM) and energy dispersive spectrometry (EDS). The results show that:the effects of single-component additive 1, 3 and 6 are better than others and the optimal dosage of them is 3wt%, 1wt% and 3wt%, respectively. The optimum combination of multi-component is 1wt% of additive 1 and 1.5wt% of additive 6. The ECS of paste with additive 10 increased more owing to the synergistic action of additive 1 with additive 6. The hydration product of Ca(OH)2 was consumed and more C-S-H gels was generated with the addition of additives in paste. Tailings particles, ettringite crystals and gels intertwined with each other, forming a dense net-like structure that filled the pores. This can significantly improve the ECS of PBM.
Reaction Mechanisms Between Molten CaF2-based Slag and Molten 9CrMoCoB Steel
Lei-zhen Peng, Zhou-hua Jiang, and Xin Geng
Accepted Manuscript Available online  8 January 2020, https://doi.org/10.1007/s12613-020-1976-5
[Abstract](42) [PDF 1314KB](5)
Abstract:
It is important to study the reaction mechanisms between slag and 9CrMoCoB in order to develop the proper ESR slag for producing the qualified ingot. In this article, the equilibrium reaction experiments between 9CrMoCoB and slag of 55%CaF2-20%CaO-3%MgO-22%Al2O3-x%B2O3 (wt%) were conducted. The reaction mechanisms between 9CrMoCoB and slag were deduced and analyzed based on the compositions of the steel and slag samples at different reaction time. Results showed that when the B2O3 content is 0.5% and FeO content ranges from 0.018% to 0.22% in the slag, B content can be controlled within the target range. When the B2O3 content is ≥ 1%, the reaction between Si and B2O3 leads to the increasement of B content. The proper SiO2 and B2O3 additional contents should be based on the ratio of[B]/[Si] in the electrode, and the SiO2 addition can inhibit the reaction between Si and Al2O3.
Giant magneto impedance effect of Co-rich amorphous fibers under magnetic interaction
Shu-ling Zhang, Wei-ye Chen, Ning Cui, Qian-qian Wu, and You-liang Su
Accepted Manuscript Available online  8 January 2020, https://doi.org/10.1007/s12613-020-1968-5
[Abstract](47) [PDF 1025KB](0)
Abstract:
The quasi metallic fibers are selected from 1 to 40 pieces and connected in parallel. The giant magneto impedance, GMI effect of Co-based melt extract fibers in bundle mode is investigated. The distribution of surface circumferential magnetic field on fibers is also analyzed induced by the driving current, which gives rise to the circular magnetization process and GMI effect. The improved GMI effect with much higher field sensitivity is observed in these fiber bundles. The results show that the field sensitivity of the four-fiber buddle at 1 MHz reaches to 1548 V/T and in six-fiber buddle the sensitivity is up to 2450 V/T at 5 MHz. The circumferential magnetic field distributed throughout the fiber's circumferential surface is rearranged and gets uneven due to the magnetic interaction among fibers. There are both strengthened and weakened magnetic field parts around these fibers' surface. The strengthened magnetic field improves the circumferential domain magnetization of the surface and results in larger GMI effects but the weakened parts inhibits the circumferential magnetization process and hence the GMI effect, which but also induces much more magnetization damp by the increased domain interactions under strong skin effect. The co-effect between the magnetic domains and the circumferential magnetization induces the optimization of the GMI effect in four-fiber bundles. The observed GMI effect proves that fibers in buddle form are performable in tailoring the sensitivity of GMI effect. And different fiber bundles could be tuned according to the working conditions, in order to manipulate the GMI response.
The effect of graphene oxide and reduced graphene oxide nanosheets on the microstructure and mechanical properties of mild steel jointing by flux-cored arc welding
Mohammad Khosravi, Mohammad Mansouri, Ali Gholami, and Yadollah Yaghoubinezhad
Accepted Manuscript , https://doi.org/10.1007/s12613-020-1966-7
[Abstract](68) [PDF 1714KB](38)
Abstract:
The effect of graphene oxide (GO) and reduced graphene oxide (RGO) nanosheets on the microstructure and mechanical properties of welded joints of mild steel was evaluated by flux-cored arc welding. GO was synthesized by the Hummer's method and was reduced under hydrothermal conditions at 180 for 12 h and 11 bar. 1, 3, and 10 mg/ml paste fillers were used in GO and RGO, and applied to the weld notch. The results clearly showed that by increasing the concentration of RGO up to 10 mg/ml, the tensile strength and hardness of the weld metal were improved by approximately 20% and 38.4%, respectively, because the coarse grains were changed into fine domains. The domain of the nanosheet cluster was about 20 nm. Specifically, the RGO nanosheets contributed to modifying the mechanical properties of the welded steel, likely due to dislocation pinning.
Kinetic analysis of austenite transformation for B1500HS high-strength steel during continuous heating process
Mu-yu Li, Dan Yao, Liu Yang, Hao-ran Wang, and Ying-ping Guan
Accepted Manuscript Available online  8 January 2020, https://doi.org/10.1007/s12613-020-1979-2
[Abstract](43) [PDF 2270KB](1)
Abstract:
The dilatometric curves of B1500HS high-strength steel under different heating rates were measured by Gleeble-3800 thermal simulator, from which the effect of heating rate on austenitization process could be obtained. The results show that the value of starting temperature Ac1 and ending temperature Ac3 of austenite transformation increase with the rise of heating rates, while the temperature interval of austenite formation decreases. The kinetic equation of austenite transformation was solved by Johnson-Mehl-Avrami (JMA) model and the related parameters of the equation were analyzed by Kissinger method. For those calculations, the activation energy of austenite transformation is 1.01×106J/mol, and the values of n and ln k0 are 0.63 and 103.03, respectively. The relationship between the volume fraction of austenite and the heating time under different heating rates could be predicted by kinetic equation. The comparison between the predicted and experimental results can verify the accuracy of the kinetic equation. By analyzing the microstructure etched by different corrosive solutions, the reliability of kinetic equation was further verified from microscopic perspective.
Effect of the lenticle to Moisture Migration in Capillary Zone of Tailings Dam
Min-jie Lian, Di Liu, Cai-wu Lu, and Wen Zhang
Accepted Manuscript Available online  8 January 2020, https://doi.org/10.1007/s12613-020-1963-x
[Abstract](49) [PDF 1134KB](0)
Abstract:
Small particle interlayer (lenticle) shows some characteristic hydraulic properties and affects the movement of unsaturated water. An online monitoring capillary water absorption device was developed by ourselves, three groups comparison tests were applied to simulate the lenticle position and thickness to the capillary rise at first time. The results show that:The characteristic about wetting front shows early rise fast, medium rise slow, later stable, the rising height in high interlayer is higher than in the lower one; Capillary water in lenticle is mainly transversal motion, the upward curve is "flat", and the longer "flat" results in the longer time; The interlayer could form the capillary stagnation zone and its moisture is close to saturation; The high interlayer may form a discontinuous wavy capillary zone. Thus, when the wetting front reaches the "coarse grain (lower)-fine grain (upper)" interface, "anti-capillary barrier effect" leads to higher moisture in the upper layer. Thus, when the wetting front of capillary water reaches the "fine grain (upper)-coarse grain (lower)" interface, "capillary barrier effect" leads the moisture content of upper tailings decreases sharply because of the horizontal movement of water in the fine medium. Obviously, the lenticle can retard the rise of capillary water and store water in it first.
Reductive leaching of indium from the residue of neutral leaching by using oxalic acid in sulfuric acid solution
F. Maddah, M. Alitabar, and H. Yoozbashizadeh
Accepted Manuscript Available online  8 January 2020, https://doi.org/10.1007/s12613-020-1974-7
[Abstract](59) [PDF 938KB](6)
Abstract:
The present study sought to assess the reductive leaching of indium from indium-bearing zinc ferrite by using oxalic acid as reducer in sulfuric acid solution. The effect of more main factors affecting the procedure on process rate, including the ratio of oxalic acid to sulfuric acid, stirring rate, grain size, temperature and the initial concentration of synergic acid was precisely evaluated. The results confirmed the acceptable efficiency of dissolving indium in the presence of oxalic acid, representing that shrinking-core model with chemical reaction controlling step can describe the kinetics of indium dissolution correctly. Based on the apparent activation energy of 44.55 KJ/mole and reaction order with respect to the acid concentration of 1.14, it was found that the presence of oxalic acid reduces sensitivity to temperature changes and increases the effect of changes in acid concentration. Finally, the equation of kinetic model based on the factors under study was presented.
Distribution Characteristics of Inclusions along the Surface Sliver Defect on Automobile Exposed Panel by Quantitative Electrolysis Method
Xiao-qian Pan, Jian Yang, Joohyun Park, and Hideki Ono
Accepted Manuscript Available online  8 January 2020, https://doi.org/10.1007/s12613-020-1973-8
[Abstract](70) [PDF 2476KB](4)
Abstract:
In this paper, for clarifying the formation mechanism of the sliver defect on the surface of automobile exposed panel, the specific distribution characteristics of inclusions along the sliver defect were studied in detailed. The three-dimensional morphology, size, composition, quantity, and distribution of inclusions in the defect and non-defect zone of automobile exposed panel were compared and analyzed with quantitative electrolysis method. It is found that the Al2O3 inclusions are in aggregated or chain-like shape along the sliver defect with the size of 3-10 μm. The Al2O3 inclusion aggregation parts are distributed discretely along the rolling direction, with 3-7 mm in spacing, 6-7 mm in length, and about 3 mm in width. The inclusion area fraction is 0.04-0.16% with an average value of 0.08%, the number density of inclusions is 40/mm2 and the average inclusion spacing is 25.13 μm. The inclusion spacing in chain-like inclusion parts is 40-160 μm with an average value of 68.76 μm. In the non-defect zone, the average area fraction and number density of inclusions are decreased to about 0.002% and 1-2/mm2, respectively, with the inclusion spacing of 400 μm, and the size of Al2O3 is 1-3 μm.
Comparative study of the Mechanical, Corrosion and Erosion-Corrosion Properties of Cast Hyper Duplex and Super Duplex Stainless Steels
Nithin Raj P, Navaneethkrishnan P K, Sekar K, and Joseph M A
Accepted Manuscript Available online  8 January 2020, https://doi.org/10.1007/s12613-020-1984-5
[Abstract](67) [PDF 921KB](1)
Abstract:
Duplex stainless steels (DSS) used in subsea structures and desalination industries require very high corrosion and erosion resistance with very excellent mechanical properties. The newly introduced cast duplex grade ASTM A890 7A has a unique composition and is expected to have much better resistance towards corrosion and erosion compared to super duplex grades 5A and 6A. This work is a comparative study of mechanical properties, corrosion and erosion-corrosion resistance of super duplex grades 5A, 6A, and the hyper duplex grade 7A. All the three grades of DSS exhibited equi-axial austenite islands in ferrite and balanced phase ratios. The hardness of the grade 7A was nearly 15% higher compared to super duplex grades, attributed to the effect of the higher content of W and Mn in 7A. Impact toughness of grade 7A was found lower compared to super duplex grades due to the carbide precipitation resulted from the partial substitution of Mo with W. The oxide layer strengthening effect of rare earth elements and higher pitting resistance equivalent number (PREN) of grade 7A resulted in higher corrosion resistance of the material. Harder and more passive grade 7A showed a 35% lower material loss during erosion-corrosion.
Effect of Calcium Content on Inclusions during LF Refining Process of AISI 321 Stainless Steel
Chao Pan, Xiao-jun Hu, Jian-chao Zheng, Ping Lin, and Kuo-chih Chou
Accepted Manuscript Available online  8 January 2020, https://doi.org/10.1007/s12613-020-1981-8
[Abstract](58) [PDF 1521KB](5)
Abstract:
During the ladle furnace (LF) refining process of AISI 321 stainless steel, the effects of three heats with different calcium contents on the evolution of inclusions were investigated. The size, morphology, and composition of inclusions were analyzed by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). After the addition of aluminum and titanium, the primary oxides in AISI 321 stainless steel were Al2O3-MgO-TiOx complex oxide, in which the mass ratio of Al2O3/MgO was highly consistent with spinel (MgO·Al2O3). After calcium treatment, the calcium content in the oxide increases significantly. The thermodynamic calculation result shows that when the Ti content was 0.2 wt%, the content of Al and Ca were below 0.1 wt% and 0.0005 wt%, respectively, which was beneficial to the formation of liquid inclusions in molten steel. The modification mechanism of calcium on TiN-wrapped oxides has been discussed in combination with temperature changes.
A review on liquid metal as cathode for molten salt/oxide electrolysis
Shu-qiang Jiao, Han-dong Jiao, Wei-li Song, Ming-yong Wang, and Ji-guo Tu
Accepted Manuscript Available online  8 January 2020, https://doi.org/10.1007/s12613-020-1971-x
[Abstract](80) [PDF 2167KB](2)
Abstract:
Compared with solid metals, liquid metals are considered as promising cathodes for molten slat/oxide electrolysis due to many fascinating advantages, such as significant depolarization effect, strong alloying effect, excellent selective separation and low operation temperature properties. After briefly introducing the properties of the liquid metal cathodes and their selection rules, in this review, we summarize the development of the liquid metal cathodes in the molten salt electrolysis, specifically in the titanium extraction, separation of actinides and rare earth metals in the halide melts. We review the recent attractive progress in preparation of liquid titanium alloys via molten oxide electrolysis, which is configured with liquid metal cathodes. Nevertheless, there are still some problems with the high-quality alloy production and large-scale applications, and therefore several research directions were discussed for further improving the quality of alloys, aiming to realize the industrial applications of the liquid metal cathodes.
Fabrication of robust Al-CNT composites using ultrasonic assembly and rolling process
Shahab Shahsavar, Mostafa Ketabchi, and Saeed Bagherzadeh
Accepted Manuscript Available online  8 January 2020, https://doi.org/10.1007/s12613-020-1969-4
[Abstract](69) [PDF 1251KB](4)
Abstract:
This study introduced a novel fabrication of Aluminum (Al)-carbon nanotube (CNT) composites employed bulk acoustic waves through accumulative roll bonding (ARB). In this method, alignment of CNT particles was performed using ultrasonic standing wave phenomenon in an aqueous media and precipitated the arrayed particles on the aluminum plate substrate. Then, the plates rolled on each other in the ARB process in three passes. The optical microscopy and scanning electron microscopy images demonstrated effective aligning of CNTs on the aluminum substrate with a negligible deviation of arrayed CNTs through the ARB process with pull out failure in some points. The X-ray diffraction (XRD) pattern proved no peak for carbon and aluminum carbide (Al4C3) in the developed composite. In addition, the tensile tests showed a significant improvement in longitudinal strength of the processed specimens with aligned CNTs in comparison with common randomly dispersed particles. The proposed technique is beneficial for fabrication of Al-CNT composite with directional mechanical strength.
Extraction and kinetic analysis of lead and strontium from leaching residue of zinc oxide ore
Xiao-yi Shen, Yuan-yong Liang, Hong-mei Shao, Yi Sun, Yan Liu, and Yu-chun Zhai
Accepted Manuscript Available online  8 January 2020, https://doi.org/10.1007/s12613-020-1972-9
[Abstract](63) [PDF 785KB](9)
Abstract:
A NH4HCO3 conversion followed by HCl leaching process was performed and was proved to be effective in extracting lead and strontium from zinc extracted residual. The mechanism of NH4HCO3 conversion and operation conditions, including molar ratio of NH4HCO3 to zinc extracted residual, NH4HCO3 concentration, conversion temperature, conversion time, and stirring velocity were discussed, and the operation conditions were optimized by orthogonal test. The experimental results indicated that NH4HCO3 conversion process in temperature ranging from 25℃ to 85℃ followed the shrinking unreacted core model and was controlled by the inner diffusion through the product layer. The extraction ratios of lead and strontium reached 85.15% and 87.08% under the optimized conditions, respectively. The values of the apparent activation energy E were 13.85 kJ·mol-1 for lead and 13.67 kJ·mol-1 for strontium, respectively.
Mechanism investigation on coal and gas outburst: An overview
Yan-kun Ma, Bai-sheng Nie, Xue-qiu He, Xiang-chun Li, Jun-qing Meng, and Da-zhao Song
Accepted Manuscript Available online  6 January 2020, https://doi.org/10.1007/s12613-019-1956-9
[Abstract](81) [PDF 1219KB](3)
Abstract:
Coal and gas outburst is a frequent dynamic disaster during underground coal mining activities. After about 150 years’ exploration, mechanism of outburst occurring is still an open question. Novel aspects of four, including physicochemical and mechanical properties of outburst-prone coal, laboratory-scale outburst experiment and numerical modeling, mine-site investigations, and doctrines of outburst mechanism, are highlighted in worldwide outburst researches. A series of outburst mechanisms are divided into two categories: single-factor and multi-factor mechanism. Multi-factor mechanism is widely accepted, but the present knowledge is insufficient to explain all statistical phenomena during a single outburst. Further topics about outburst mechanism are proposed by summarizing the phenomena that need a more precise explanation. The most appealing research is the microscopic process of the interaction of coal and gas. The updated modern physic-chemical methods can help to deeply understand the natural properties of outburst-prone coal. Outburst experiment can make up for the deficiency of first-hand observing data at the scene. It is very meaningful that original outburst scene is restored by constructing a geomechanical model or numerical model and reproducing the entire outburst process based on the mining environment conditions, including stratigraphic distribution, gas occurrence, and geological structure. Finally, outburst mechanism at microscale can be a trend for further study.
A review of gold extraction using non-cyanide lixiviants: Fundamentals, advancements and challenges toward alkaline sulfur-containing leaching agents
Chun-bao Sun, Xiao-liang Zhang, Jue Kou, and Yi Xing
Accepted Manuscript Available online  6 January 2020, https://doi.org/10.1007/s12613-019-1955-x
[Abstract](99) [PDF 1204KB](6)
Abstract:
The alkaline sulfur-containing lixiviants, including thiosulfate, polysulfides, and alkaline sulfide solutions, stand out as a promising class of alternatives to cyanide owing to their low toxicity, high efficiency and strong adaptability. In this paper, we summarized the research progress and facing challenges in gold extraction using these non-cyanide reagents. After a brief introduction to the preparation method, the transformation process of various sulfur-containing species in alkaline solutions was discussed. Thereafter, some insights into the mechanism of gold leaching in alkaline sulfur-containing solutions were presented from different aspects, including thermodynamics analysis, electrochemical dissolution and leaching kinetics. Moreover, recent progress on in-situ generation of sulfur-containing anions from gold-bearing sulfide minerals was outlined as well. Ultimately, gold passivation caused by sulfur species was particularly discussed, which was considered the greatest challenge facing sulfur-containing leaching systems. It is expected that alkaline sulfur-containing lixiviants will serve as alternatives for industrial applications of gold extraction, particularly for refractory gold ores containing copper and carbonaceous matter.
Comparative studies on the hot corrosion behavior of air plasma spray and high velocity oxygen fue -coatedCo-based L605 superalloys in a gas turbine environment
Jithesh K and Arivarasu M
Accepted Manuscript Available online  3 January 2020, https://doi.org/10.1007/s12613-019-1943-1
[Abstract](57) [PDF 3465KB](0)
Abstract:
Improvements in the corrosion resistance of alloys at elevated temperature is a factor for their potential use in gas turbines. L605 is one such alloy that exhibits exceptional mechanical properties at ambient temperature but shows poor corrosion resistance at elevated temperature. In this study, CoNiCrAlY was coated on the L605 alloy using air plasma spray (APS) and high velocity oxygen fuel (HVOF) coatings to improve the hot corrosion resistance in a gas turbine engine environment at 850℃ for 50 cycles. Each cycle included 1 h of heating in a tubular furnace and 20 min if cooling at ambient temperature, followed by measuring their weight using an electronic weight balance. The weight gain/loss and corrosion rate were analyzed to determine the corrosion resistance of these samples. The surface and cross section of the corroded sample were examined by scanning electron microscopy and energy-dispersive X-ray spectroscopy. For phase identification on the hot-corroded samples, XRD analysis was performed. The HVOF-sprayed sample showed better results compared to the APS sample due to its lower porosity, less internal oxidation, and much less weight gain in the hot corrosion environment.
Comparison of α particle detectors based on single-crystal diamond films grown in two types of gas atmospheres by microwave plasma-assisted chemical vapor deposition
Yan-zhao Guo, Jin-long Liu, Jiang-wei Liu, Yu-ting Zheng, Yun Zhao, Xiao-lu Yuan, Zi-hao Guo, Li-fu Hei, Liang-xian Chen, Jun-jun Wei, Jian-peng Xing, and Cheng-ming Li
Accepted Manuscript Available online  30 December 2019, https://doi.org/10.1007/s12613-019-1944-0
[Abstract](64) [PDF 876KB](0)
Abstract:
Chemical vapor deposition (CVD)-grown diamond films have been developed as irradiation-resistant materials to replace or upgrade current detectors for use in extreme radiation environments. However, their sensitivity in practical applications has been inhibited by space charge stability issues caused by defects and impurities in pure diamond crystal materials. In this study, high-quality CVD-grown single-crystal diamond (SCD) detectors based on different ppb grades of nitrogen impurities were fabricated and characterized. The intrinsic properties of the SCD samples were characterized using Raman spectroscopy, stereomicroscopy, X-ray diffraction with the rocking curve mode, cathode luminescence (CL) and infrared and ultraviolet-visible-near infrared spectroscopies. After packaging the detectors, the dark current and energy resolution under α particle irradiation were investigated. Dark currents of less than 5 pA at 100 V were obtained after annealing the electrodes, which is comparable with the optimal value previously reported. The detector that uses a diamond film with a higher nitrogen content showed poor energy resolution, whereas the detector with more dislocations had a poor charge collection efficiency (CCE). This demonstrates that the nitrogen content in diamond has a significant effect on the energy resolution of detectors, while the dislocations in diamond largely contribute to the poor CCE of detectors.
Suspension Calcination and Alkali Leaching of Low-grade High-sulfur Bauxite: Desulfurization, Mineralogical Evolution, and Desilication
Hong-fei Wu, Jun-qi Li, Chao-yi Chen, Fei-long Xia, and Zhen-shan Xie
Accepted Manuscript Available online  30 December 2019, https://doi.org/10.1007/s12613-019-1941-3
[Abstract](56) [PDF 1136KB](0)
Abstract:
To enable the utilization of low-grade and high-sulfur bauxite, suspension calcination was used to remove the sulfur and the activate silica minerals and the calcinated bauxite was subjected to a desilication process in NaOH solution under atmospheric pressure. The desulfurization and desilication properties and mineralogical evolution were studied by X-ray diffraction, thermogravimetry-differential thermal analysis, scanning electron microscopy, and FactSage methods. The results demonstrated that the suspension calcination method was efficient for sulfur removal:84.21% of S was removed after calcination at 1000℃ for 2 min. During the calcination process, diaspore and pyrite were transferred to α-Al2O3, magnetite, and hematite. The phase transformation of pyrite follows the order FeS2 → Fe3O4 → Fe2O3, and the iron oxides and silica were converted into iron silicate. In the alkali-soluble desilication process, the optimum conditions were an alkali solution concentration of 110 g/L, a reaction time of 20 min, and a reaction temperature of 95℃. The corresponding desilication ratio and alumina loss ratio were 44.9% and 2.4%, respectively, and the alumina-to-silica mass ratio of the concentrate was 7.9. The Al2O3·2SiO2, SiO2, and Al2O3 formed during the calcination process could react with NaOH solution, and their activity decreased in the order Al2O3·2SiO2 > SiO2 > Al2O3.
Fatigue limit assessment of a 6061 aluminum alloy based on infrared thermography and steady ratcheting effect
Ru-yi Feng, Wen-xian Wang, Zhi-feng Yan, Deng-hui Wang, Shi-peng Wan, and Ning Shi
Accepted Manuscript Available online  30 December 2019, https://doi.org/10.1007/s12613-019-1942-2
[Abstract](90) [PDF 997KB](4)
Abstract:
In this study, the temperature evolution and ratcheting strain of a 6061 aluminum alloy under cyclic loading was measured. The temperature evolution measured by infrared thermography was closely related to the cyclic loading. The mechanism of the temperature evolution under different cyclic loading levels was analyzed according to thermoelastic, viscous, and thermoplastic effects. Additionally, the evolution of the ratcheting strain under cyclic loading above the fatigue limit underwent three stages:the first increasing stage, the second steady state, and final abrupt increase stage. The fatigue limit of the 6061 aluminum alloy was estimated according to the cyclic strength that corresponds with an obvious increase in the steady value in the second stage of the temperature and ratcheting strain. The traditional S-N curve was also used for comparison and proving the feasibility of the two methods.
Causes and detection of coalfield fires, control techniques, and heat energy recovery: A review
He-tao Su, Fu-bao Zhou, Bo-bo Shi, Hai-ning Qi, and Jin-chang Deng
Accepted Manuscript Available online  25 December 2019, https://doi.org/10.1007/s12613-019-1947-x
[Abstract](103) [PDF 1361KB](4)
Abstract:
Coalfield fires are considered a global crisis that contributes significantly to environmental destruction and loss of coal resources and poses a serious threat to human safety and health. In this paper, research related to the initiation, development, and evolution of coalfield fires is reviewed. The existing detection and control techniques of coalfield fires are also reviewed. Traditional firefighting is associated with waste of resources, potential risks of recrudescence, potential safety hazards, extensive and expensive engineering works, and power shortages. Recently, coalfield fires have been recognized as having significant potential for energy conservation and heat energy recovery. Thermoelectric power generation is regarded as a suitable technology for the utilization of heat from coalfield fires. The extraction of heat from coalfield fires can also control coalfield fires and prevent reignition leading to combustion. Technologies for absorbing heat from burning coal and overlying rocks are also analyzed. In addition, the control mode of "three-region linkage" is proposed to improve firefighting efficiency. Integrating heat energy recovery with firefighting is an innovative method to control coalfield fires.
Effects of chelating agent on sol-gel synthesis of nano zirconia: The comparison of Pechini and sugar-based methods
Faramarz Kazemi, Farzin Arianpour, Mahdiar Taheri, Ali Saberi, and Hamid Reza Rezaie
Accepted Manuscript Available online  6 November 2019, https://doi.org/10.1007/s12613-019-1933-3
[Abstract](140) [PDF 1944KB](10)
Abstract:
This study reports on the comparison of the Pechini and sugar-based combustion synthesis to produce nano zirconia. It involves utilizing zirconium hydroxide as a metal precursor and citric acid, sucrose and fructose as chelating agents, followed by calcination at 500, 600, and 700℃ in air. The characterizations were thermal analysis, specific surface area, Fourier transform infra-red spectroscopy, X-ray diffraction, scanning, and transmission electron microscopy. The highest specific surface area (27 m2 g-1) and smallest particle size (39.1 nm) were obtained for fructose at 700℃. The X-ray study revealed the formation of the single phase tetragonal zirconia via fructose after calcination at 500℃, while for sucrose and citric acid, mixtures of monoclinic and tetragonal phases were obtained. The tetragonality parameter was determined using diffraction data and proved it increases with increasing the temperature. The presence and formation mechanism of the stabilized tetragonal zirconia were also discussed based on the X-ray and electron diffraction studies.
Effect of chemical activation process on adsorption of As(V) ion from aqueous solution by mechano-thermally synthesized Zinc Ferrite nanopowder
Mohammad Sefidmooy Azar, Shahram Raygan, and Saeed Sheibani
Accepted Manuscript Available online  6 November 2019, https://doi.org/10.1007/s12613-019-1931-5
[Abstract](87) [PDF 2500KB](1)
Abstract:
In this study, nanostructured ZnFe2O4 was synthesized by heat treatment of a mechanically activated mixture of ZnO/α-Fe2O3. XRD and DTA results demonstrated that, after 5h mechanical activation of the mixture, ZnFe2O4 was formed by heat treatment at 750℃ for 2h. To improve the characteristics of ZnFe2O4 for adsorption application, the chemical activation process was performed. The 2h chemical activation with 1mol.L-1 HNO3 and co-precipitation of 52-57% dissolved ZnFe2O4 led to an increment of saturated magnetization from 2.0 to 7.5 emu.g-1 and specific surface area from 5 to 198 m2.g-1. Also the observed particle size reduction of chemically activated ZnFe2O4 in FESEM micrographs was in agreement with the specific surface area increment. These improvements in ZnFe2O4 characteristics had a significant effect on the adsorption performance of this adsorbent. Adsorption results revealed that mechano-thermally synthesized ZnFe2O4 had the maximum arsenic adsorption of 38% with the adsorption capacity of 0.995mg.g-1 in the 130mg.L-1 solution of As(V) and agitation time of 30min. However, chemically activated ZnFe2O4 showed the maximum arsenic adsorption of about 99% with the adsorption capacity of 21.460mg.g-1 in the same condition. These results showed that the weak adsorption performance of mechano-thermally synthesized ZnFe2O4could be improved by the chemical activation process.
The evolution of pore structure during coke graphitization process in the blast furnace hearth
Wen-long Zhan, Hao-bin Zhu, Zhi-jun He, Ying-chang Yu, Qing-hai Pang, and Jun-hong Zhang
Accepted Manuscript Available online  6 November 2019, https://doi.org/10.1007/s12613-019-1927-1
[Abstract](98) [PDF 524KB](3)
Abstract:
The pore structure was one of the important factors influencing coke strength, which was essential to maintain gas and liquid permeability in the blast furnace hearth. An in-depth understanding of pore structure evolution during the graphitization process can help to reveal the coke behavior during its descent in a blast furnace. The coke graphitization was simulated at different heating temperatures from 1100℃ to 1600℃ at intervals of 100℃. The quantitative evaluation of coke pore structure with different graphitization degree was determined by vacuum drainage and nitrogen adsorption method. With the increase of heating temperature, the apparent porosity, specific surface area, pore volume and the amount of micro pores showed a good correlation, which can be divided into three processes:1100-1200℃, 1200-1400℃ and 1400-1600℃. When temperature was below 1400℃, ash migration from the inner part mainly led to changes of coke pore structure. While, once the temperature was higher than 1400℃, it was mainly affected by coke graphitization degree. There were intersection points in the adsorption and desorption curves of coke with different graphitization degree, and the two curves did not coincide and formed a "hysteresis loop". Based on the principle of hysteresis loop analysis, it was believed that the porous structure of graphitized coke mostly appeared as a shape of "hair follicle". Scanning electron microscopy (SEM) and Energy Dispersive Spectrometer (EDS) analysis also showed that the migration of the internal ash to the surface of the matrix during the graphitization process until 1400℃ was attributed to that changes.
Temperature-Dependent Evolution of Oxide Inclusions during Heat Treatment of Stainless Steel with Yttrium Addition
Xue-liang Zhang, Shu-feng Yang, Jing-she Li, and Jin-qiang Wu
Accepted Manuscript Available online  6 November 2019, https://doi.org/10.1007/s12613-019-1935-1
[Abstract](158) [PDF 1697KB](33)
Abstract:
Evolution of oxide inclusions during isothermal heating of 18Cr-8Ni stainless steel with yttrium addition at temperatures of 1273 K to 1573 K was investigated systematically. Homogeneous spherical Al-Y-Si-Mn(-Cr)-O inclusions were observed in as-cast steel. After heating, most of the homogeneous inclusions transformed to heterogeneous ones with Y-rich and Al-rich parts, even though some homogeneous oxide particles were still found at 1273 K and 1573 K. With increasing heating temperature, more large-sized inclusions formed, and the shape of inclusions also changed from spherical to irregular. The maximum transformation temperature of inclusions was determined to be 1373 K. The evolution mechanism of inclusions during heating was proposed to be the mutual effects of (i) internal transformation of inclusions owing to crystallization of glassy oxide and (ii) interfacial reaction between inclusions and steel matrix, while the internal transformation of inclusions was considered to be the main factor at heating temperatures less than 1473 K.
Stress-corrosion behavior and characteristics in friction stir welding of AA2198-T34 alloy
Quan-qing Zeng, Songsheng Zeng, and Dongyao Wang
Accepted Manuscript Available online  6 November 2019, https://doi.org/10.1007/s12613-019-1924-4
[Abstract](88) [PDF 837KB](4)
Abstract:
To better understand the stress corrosion behavior of the friction stir welding (FSW), the effects of microstructure on stress corrosion behavior of the FSW in 2198-T34 aluminum alloy were investigated. The experimental results show that the low-angle grain boundary (LABs) of stir zone (SZ) of friction stir welding is significantly less than that of heated affected zone (HAZ), thermo-mechanically affected zone (TMAZ) and parent materials (PM), but grain boundary precipitates (GBPs) T1(Al2CuLi)are less, which has slight effect on stress corrosion. The dislocation density in SZ is higher than that in other regions. The residual stress in SZ is +67 MPa, which is larger than that in TMAZ. The residual stress in HAZ and PM is -8 MPa and -32 MPa, respectively, and are both compressive stresses. The corrosion potential in SZ is obviously lower than that in other regions. However, micro-cracks were formed in the SZ at low strain rate. This indicates that grain boundary characters and GBPs have no significant effects on the crack initiation in stress corrosion process of AA2198-T34. Nevertheless, residual tensile stress has significant effects on crack initiation during stress corrosion process.
Design of GO/TiO2 One-Dimensional Photonic Crystal Photocatalytic Photocatalysts with Improved Photocatalytic Activities for Tetracycline
Huan-huan Wang, Wen-xiu Liu, Jing Ma, Qian Liang, Wen Qin, Patrick Osei Lartey, and Xiao-jiang Feng
Accepted Manuscript Available online  6 November 2019, https://doi.org/10.1007/s12613-019-1923-5
[Abstract](80) [PDF 902KB](1)
Abstract:
In this work, (GO/TiO2)N one-dimensional photonic crystal with different lattice constants was prepared via sol-gel method and their transmission characteristics for photocatalysis was tested. The results showed that the lattice constant, filling ratio, periodic number and incident angle had effects on the band gap. When the lattice constant, filling ratio, number of periodic layers and incident angle were set at 125 nm, 0.45, 21 layers and 0° respectively, the band gap width of 53 nm appeared at the central wavelength (322 nm). The absorption peak of the photocatalyst at 357 nm was overlapped the blue edge of the photonic band gap. A slow photon effect region above 96% reflectivity appeared. The degradation rate of tetracycline in (GO/TiO2)N photonic crystal were enhanced 64% within 60 min. Meanwhile, the degradation efficiency effectively had been improved at the same ratio, compared to that of GO/TiO2 composite film and GO/TiO2 powder.
The luminescence properties of nitrogen-rich Ca-Sialon: Eu2+ phosphors prepared by freeze-drying assisted combustion synthesis
Zhang-lin Chen, Kai Liu, Xuan-yi Yuan, and Ke-xin Chen
Accepted Manuscript Available online  6 November 2019, https://doi.org/10.1007/s12613-019-1934-2
[Abstract](85) [PDF 1771KB](1)
Abstract:
The nitrogen-rich Eu2+ doped Ca-α-Sialon phosphors (Cam/2-xSi12-m-nAlm+nOnN16-n:xEu) were synthesized by a freeze-drying assisted combustion synthesis (CS) route. Fast-synthesized products with high purity and uniform particle morphology were confirmed by X-ray diffraction (XRD) and scanning electron microscope (SEM). The analysis of lattice parameters by comparing with empirical equations provided evidence that the as-prepared phosphors were low in oxygen content. A series of samples were prepared according to the stoichiometry of Cam/2-0.08Si12-mAlmN16:0.08Eufor further research. The influences of m value on the luminescence properties were investigated in detail. As m increased, a red-shift phenomenon was observed in both the excitation and emission spectrum. First-principles electronic structure calculations showed that 3d energy level of Ca plays an important role in this red-shift phenomenon.
Processing of AM60 magnesium alloy by hydrostatic cyclic expansion extrusion at elevated temperature as a new SPD method
Farshad Samadpour, Ghader Faraji, and Armin Siahsarani
Accepted Manuscript Available online  6 November 2019, https://doi.org/10.1007/s12613-019-1921-7
[Abstract](153) [PDF 1364KB](9)
Abstract:
In this study, hydrostatic cyclic expansion extrusion (HCEE) process at elevated temperatures is proposed as a method for processing of less deformable materials such as magnesium and production of long-length ultrafine-grained rods. In the HCEE process at elevated temperatures, high-pressure molten linear low-density polyethylene (LLDPE) was used as a fluid to eliminate frictional forces. To study the capability, AM60 magnesium rods were processed and the properties were investigated. It was revealed that the mechanical properties are improved significantly after the HCEE process. Yield and ultimate strength increase from initial values of 138 and 221 MPa to 212 and 317 MPa, respectively. Also, elongation is enhanced from 15% to 22% due to the refined grains and existence of high hydrostatic pressure. Furthermore, microhardness is increased from 57 HV to 70 HV. Also, the microstructural analysis reveals that ultrafine-grained structure could be produced by the HCEE process; moreover, the size of the particles decreases and these particles thoroughly scatter between the grains. Finite element analysis shows that the HCEE is independent of the length of the sample, which makes the process suitable for industrial application.
Wire and arc additive manufacturing of 4043 Al-alloy using a CMT method
Zhi-qiang Liu, Pei-lei Zhang, Shao-wei Li, Di Wu, and Zhi-shui Yu
Accepted Manuscript Available online  6 November 2019, https://doi.org/10.1007/s12613-019-1930-6
[Abstract](76) [PDF 2154KB](4)
Abstract:
A CMT+PULSE(C+P) arc was applied in the additive manufacturing of 4043 Al-alloy parts. Parameters for making parts were investigated. The properties and microstructure of the parts were researched. Experimental results showed that welding a speed of 0.008 m/s and a wire feeding speed of 0.067 m/s was suitable to manufacture thin-walled parts, and the reciprocating scanning method could be adopted to manufacture thick-walled parts. The thin-walled part of the C+P mode has fewer pores than the CMT mode. The tensile strength of C+P thin-wall parts ranges up to 172 MPa. Thick-walled parts have a maximum tensile strength of 178 MPa. Hardness decreases at the interface and in the coarse dendrite and increases in the refined grain area.
Exfoliation of poly (ethylene glycol)-intercalated Graphite Oxide composite in water without sonication
Yang Hu, Chun-bao Sun, and Jue Kou
Accepted Manuscript Available online  6 November 2019, https://doi.org/10.1007/s12613-019-1932-4
[Abstract](86) [PDF 783KB](1)
Abstract:
A novel method for exfoliating graphite oxide (GrO) was implemented in this paper through the mass water-adsorption of GrO-poly (ethylene glycol) (GrO-PEG) composite. The GrO-PEG composite was prepared by intercalating PEG into the lamellas of GrO and the variation of basal spacing was measured by X-ray diffraction. The yield of graphene was measured with an ultraviolet spectrophotometer and the properties of graphene oxide were characterized by atomic force microscope (AFM), transmission electron microscope (TEM), Raman spectrum and Fourier transform infrared spectroscopy (FTIR). It was found that the increase of intercalation time would improve the yield of graphene oxide, while increasing the PEG molecular weight had the opposite effect. The graphene oxide sheets produced from the intercalation-absorption-exfoliation process were found to be as a four-layer structure. Results of TEM and Raman analysis indicated that the graphitized structure and oxygen groups of GO would preserve during the exfoliation. Above all, it can be concluded that graphene oxide with good quality could be prepared by a mildly method through the water adsorption of GrO-PEG composite.
Growth of solidified shell in bloom continuous casting mold of hypo-peritectic steel based on FeS tracer method
Da-peng Li, Hua-zhang Wu, Hai-feng Wang, and Hong Li
Accepted Manuscript Available online  29 October 2019, https://doi.org/10.1007/s12613-019-1907-5
[Abstract](73) [PDF 542KB](1)
Abstract:
An industrial experiment was performed to investigate shell growth in the mold region. Here, FeS tracer was added to molten steel in a bloom continuous casting mold of hypo-peritectic steel, and the distributions of solidified shells along the mold height and circumference were obtained. The results showed that there were three weak regions of solidification in the casting direction at the moment of FeS addition. In the range of 90-210 mm under the meniscus in the mold, the shell thickness periodic fluctuation was closely related to the periodic fluctuation of the air gap and was influenced by the peritectic transformation. When moving to the lower part of the mold, the shell remelted because of the stream impinging. After the departure from the mold, a slight shell thinning was observed with the reduction of the cooling intensity. The inner side of the bloom exhibited non-uniform shell growth while the narrow faces and the outer side exhibited relatively regular growth in shell thickness, which was likely due to the curved mold being employed. On the transverse section, the thinnest shells were located in the off-corners.
Durability performance and microstructure analysis of a road base material prepared from red mud and flue gas desulfurization fly ash
Emile Mukiza, Lingling Zhang, and Xiaoming Liu
Accepted Manuscript Available online  28 October 2019, https://doi.org/10.1007/s12613-019-1915-5
[Abstract](161) [PDF 1199KB](14)
Abstract:
The present study aimed to investigate the durability and microstructure evolution of road base materials prepared from red mud and flue gas desulfurization fly ash. The microstructure was characterized using scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, Mercury intrusion porosimetry, and 27Al magic-angle spinning nuclear magnetic resonance spectroscopy, whereas inductive coupled plasma mass spectrometry was adopted to characterize the leaching behavior of hazardous compounds. The durability testing showed that the strength reached 3.81 MPa, 4.87 MPa, and 5.84 MPa after 5 freezing-thawing cycles and 5.21 MPa, 5.75 MPa, and 6.98 MPa after 20 wet-dry cycles for RBM1, RBM2, and RBM3, respectively. Microstructure analysis indicated that hydration products were continuously formed even during wet-dry and freezing-thawing exposure and were responsible for the strength and durability of the road base material (RBM). The observed increase in mesopores (50 nm-1 μm) and macropores (>1 μm) after freezing-thawing and wet-dry exposure suggested that the mechanism for RBMs deterioration is pore enlargement due to cracks that develop inside their matrix. Moreover, the freezing-thawing showed a greater negative effect on the road base durability than wet-dry exposure. The leaching tests showed that sodium and heavy metals were solidified below the minimum requirement, which makes these materials suitable for use as a natural material replacement in road base construction materials.
Microstructure and Mechanical Properties of High-Strength Low Alloy Steel by Wire and Arc Additive Manufacturing
Yili Dai, Shengfu Yu, Anguo Huang, and Yusheng Shi
Accepted Manuscript Available online  28 October 2019, https://doi.org/10.1007/s12613-019-1919-1
[Abstract](70) [PDF 4059KB](10)
Abstract:
A high-building multidirectional pipe joint was fabricated by wire and arc additive manufacturing using high-strength low alloy (HSLA) steel. The microstructure characteristics and transformation of the HSLA were observed and analyzed. The results show that the forming part included four regions:a solidification zone, complete austenitizing zone, partial austenitizing zone, and a tempering zone. The solidification zone solidified as typical columnar crystals from a molten pool. The complete austenitizing zone formed from the solidification zone heated to a temperature greater than 1100℃, and the typical columnar crystals in the complete austenitizing zone were difficult to observe. The partial austenitizing zone formed from the completely austenite zone heated between Ac1 and 1100℃, which is mainly equiaxed grains. After several thermal cycles with peak temperature of 600℃, the partial austenitizing zone transformed to the tempering zone, which consisted of fully equiaxed grains. From the solidification zone to the tempering zone, because of the precipitation of inclusions (ZrO2·Al2O3·MnO·SiO2·MnS) and several thermal cycles, the contents of pro-eutectoid ferrite (PF) and ferrite side plate (FSP) decreased, whereas the contents of acicular ferrite (AF) and fine grain ferrite (FGF) increased; in addition, the average grain size decreased from 75 μm to 20 μm. The final microstructure consisted of FGF and pearlite; the tensile strength was approximately 564 MPa, and the impact toughness was approximately 108 J, satisfying the requirement for the intended application.
Cu2+-catalyzed mechanism in oxygen-pressure acid leaching of artificial sphalerite
Lei Tian, Ao Gong, Xuan-gao Wu, Yan Liu, Zhi-feng Xu, and Ting-an Zhang
Accepted Manuscript Available online  28 October 2019, https://doi.org/10.1007/s12613-019-1918-2
[Abstract](75) [PDF 1099KB](1)
Abstract:
Artificial sphalerite, as a raw material, and the catalytic mechanism of a Cu2+ catalyst system for the dissolution of sphalerite, were investigated using a potential autoclave. The leaching behaviors of Zn and Cu for artificial sphalerite dissolution at 363 K-423 K and 423 K-483 K were investigated. The system potential exhibited a steady downward trend with increasing leaching time at 363 K-423 K. The highest leaching rate of Zn was only 52.7%. Further, scanning electron microscopy (SEM)-energy-dispersive X-ray spectroscopy (EDS) showed that Cu2+ reacted with H2S to form CuS, which was deposited on the surface of the sphalerite and hindered the leaching reaction. When the temperature exceeded 463 K, the system potential showed a steady upward trend, and the leaching rate of Zn exceeded 97%. SEM-EDS revealed that the temperature increase caused the CuS deposited on the mineral surface to dissolve, which was beneficial to the cyclic catalysis of Cu2+. Furthermore, the kinetics of leaching at 363-423 K and 423-483 K were investigated and a kinetic equation for fitting the results was formulated. The activation energies of zinc leaching were 38.66 kJ/mol and 36.23 kJ/mol at 363K -423 K and 423 K-483 K, indicating that the processes were controlled by surface chemical reactions and the presence of Cu2+ is advantageous for oxygen-pressure acid leaching of sphalerite at elevated temperatures.
Kinetics of hydrogarnet carbonation with different silica saturation coefficients
Xiao-feng Zhu, Ting-an Zhang, and Guo-zhi Lv
Accepted Manuscript Available online  28 October 2019, https://doi.org/10.1007/s12613-019-1913-7
[Abstract](88) [PDF 1338KB](4)
Abstract:
Carbonated decomposition of hydrogarnet is one of the vital reactions of the novel eco-friendly calcification-carbonation method, which is designed to dispose of low-grade bauxite and Bayer red mud. In this study, the potential effects of the silica saturation coefficient (x) on the carbonated decomposition of hydrogarnet were investigated from the kinetic perspectives. Results showed that the x values of synthesized hydrogarnets with pure reagent at 60℃, 120℃, 180℃, and 240℃ were 0.27, 0.36, 0.70, and 0.73, respectively. The carbonated decomposition of hydrogarnet with different x values underwent two stages with significantly different rates, and the kinetic mechanisms of the two stages can be described by the kinetic functions R3 and D3. The apparent activation energies at Stages 1 and 2 were 41.96-81.64 and 14.80-34.84 kJ/mol, respectively. Moreover, the corresponding limiting steps of the two stages were interfacial chemical reaction and diffusion.
A study of properties of ultrafine bainitic steel under low austempering temperature
Wei Liu, Youhui Jiang, Hui Guo, Yue Zhang, Aimin Zhao, and Yao Huang
Accepted Manuscript Available online  28 October 2019, https://doi.org/10.1007/s12613-019-1916-4
[Abstract](91) [PDF 3715KB](7)
Abstract:
The mechanical properties and wear resistance of the ultra-fine bainitic steel austempered at various temperatures were investigated. Scanning electron microscopy (SEM) and X-ray diffraction were used to analyze the microstructure. The worn surfaces were observed via laser scanning confocal microscopy and SEM. Results indicated that, under low austempering temperatures, the mechanical properties differed, and the wear resistance remained basically unchanged. The tensile strength of the samples was above 1800 MPa, but only one sample austempered at 230℃ had an elongation of more than 10%. The sample weight loss was approximately linear with the cycles of wear and nonlinear with the loads. The samples showed little difference in wear resistance at different isothermal temperatures, whereas the thickness of their deformed layers varied greatly. The results are related to the initial hardness of the sample and the stability of the retained austenite. Meanwhile, the experimental results show that the effect of austempering temperatures on the wear resistance of ultra-fine bainitic steel can be neglected under low applied loads and low austempering temperature.
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Effect of hot rolling and annealing temperature on the microstructure and mechanical properties of SP-700 alloy
Parnia Parvizian, Maryam Morakabati, and Saeed Sadeghpour
In press, Uncorrected proof  Available online  6 November 2019, https://doi.org/10.1007/s12613-019-1922-6
[Abstract](74) [FullText HTML](1) [PDF 1422KB](6) SpringerLink
Abstract:
The effect of rolling temperature on both two- and single-phase regions and annealing in a temperature range of 700–950°C on the microstructure and mechanical properties of Ti‒5Al‒4V‒2Fe‒1Mo alloy was investigated. The results indicated that the best balance of strength and ductility is obtained by rolling in the two-phase region due to the globularization of the alpha phase and increase in its volume fraction. After rolling in the two-phase region, the ductility of the specimens annealed at 700 to 800°C increased because of the finer size and globularized alpha phase, while the reduction in strength was attributed to a decrease in the alpha phase volume fraction. However, at 950°C, the strength increased and ductility dropped by the formation of acicular alpha phase due to an increase in the phase boundary area. Annealing and aging after rolling in the beta-phase region increased the strength and decreased the ductility, which is attributed to the formation of a secondary alpha phase. A combination of favorable yield strength (1113 MPa) and elongation (13.3%) was obtained through rolling at 850°C followed by annealing at 750°C and aging at 570°C.
Microstructural analysis and hot corrosion behavior of HVOF-sprayed Ni–22Cr–10Al–1Y and Ni–22Cr–10Al–1Y–SiC (N) coatings on ASTM-SA213-T22 steel
Gurmail Singh, Niraj Bala, and Vikas Chawla
In press, Uncorrected proof  Available online  15 February 2020, https://doi.org/10.1007/s12613-019-1946-y
[Abstract](14) [FullText HTML](0) [PDF 5256KB](0) SpringerLink
Abstract:
The present paper deals with the investigation of microstructure and high-temperature hot corrosion behavior of high-velocity oxy fuel (HVOF)-produced coatings. Two powder coating compositions, namely, Ni22Cr10Al1Y alloy powder and Ni22Cr10Al1Y (80wt%; micro-sized)–silicon carbide (SiC) (20wt%; nano (N)) powder, were deposited on a T-22 boiler tube steel. The hot corrosion behavior of bare and coated steels was tested at 900 °C for 50 cycles in Na2SO4–60wt%V2O5 molten-salt environment. The kinetics of corrosion was established with weight change measurements after each cycle. The microporosity and microhardness of the as-coated samples have been reported. The X-ray diffraction, field emission-scanning electron microscopy/energy dispersive spectroscopy, and X-ray mapping characterization techniques have been utilized for structural analysis of the as-coated and hot-corroded samples. The results showed that both coatings were deposited with a porosity less than 2%. Both coated samples revealed the development of harder surfaces than the substrate. During hot corrosion testing, the bare T22 steel showed an accelerated corrosion in comparison with its coated counterparts. The HVOF-sprayed coatings were befitted effectively by maintaining their adherence during testing. The Ni22Cr10Al1Y–20wt%SiC (N) composite coating was more effective than the Ni–22Cr–10Al–1Y coating against corrosion in the high-temperature fluxing process.
Research on new beneficiation process of low-grade magnesite using vertical roller mill
Chuang Li, Chuan-yao Sun, Yu-lian Wang, Ya-feng Fu, Peng-yun Xu, and Wan-zhong Yin
In press, Uncorrected proof  Available online  14 February 2020, https://doi.org/10.1007/s12613-019-1898-2
[Abstract](15) [FullText HTML](0) [PDF 1243KB](1) SpringerLink
Abstract:
In this study, we investigated whether the vertical roller mill can be efficiently used in the beneficiation of low-grade magnesite and whether it can improve upon the separation indices achieved by the ball mill. We conducted experiments involving the reverse flotation and positive flotation of low-grade magnesite to determine the optimum process parameters, and then performed closed-circuit beneficiation experiments using the vertical roller mill and ball mill. The results show that the optimum process parameters for the vertical roller mill are as follows: a grinding fineness of 81.6wt% of particles less than 0.074 mm, a dodecyl amine (DDA) dosage in magnesite reverse flotation of 100 g·t−1, and dosages of Na2CO3, (NaPO3)6, and NaOL in the positive flotation section of 1000, 100, and 1000 g·t−1, respectively. Compared with the ball mill, the use of the vertical mill in the beneficiation of low-grade magnesite resulted in a 1.28wt% increase in the concentrate grade of MgO and a 5.88% increase in the recovery of MgO. The results of our causation mechanism analysis show that a higher specific surface area and greater surface roughness are the main reasons for the better flotation performance of particles ground by the vertical roller mill in the beneficiation of low-grade magnesite.
Model prediction of the effect of in-mold electromagnetic stirring on negative segregation under bloom surface
Yu-kun Huo, Li-hua Zhao, Hang-hang An, Min Wang, and Chang-dong Zou
In press, Uncorrected proof  Available online  29 October 2019, https://doi.org/10.1007/s12613-019-1906-6
[Abstract](97) [FullText HTML](1) [PDF 1049KB](4) SpringerLink
Abstract:
Aiming at the problem of negative segregation under a bloom surface, a coupling macrosegregation model considering electromagnetic field, flow, heat, and solute transport was established based on the volume average method to study the effect of in-mold electromagnetic stirring (M-EMS) on the negative segregation under the bloom surface. In the model, the influence of dendrite structure on the flow and solute transport was described by the change of permeability. The model was validated by the magnetic induction intensity of M-EMS and carbon segregation experiment. The results show that the solute C in the solidified shell in the turbulent zone of the bloom undergoes two negative segregations, whereby the first is caused by nozzle jet, and the second by the M-EMS. The severities of the negative segregation caused by M-EMS at different currents and frequencies are also different, and the larger the current is, or the smaller the frequency is, the more serious will be the negative segregation. With the M-EMS, the solute C distribution in the liquid phase of the bloom is more uniform, but the mass fraction of C in the liquid phase is higher than that without M-EMS.
Machine-learning-assisted prediction of the mechanical properties of Cu–Al alloy
Zheng-hua Deng, Hai-qing Yin, Xue Jiang, Cong Zhang, Guo-fei Zhang, Bin Xu, Guo-qiang Yang, Tong Zhang, Mao Wu, and Xuan-hui Qu
In press, Uncorrected proof  Available online  17 January 2020, https://doi.org/10.1007/s12613-019-1894-6
[Abstract](70) [FullText HTML](0) [PDF 967KB](13) SpringerLink
Abstract:
The machine-learning approach was investigated to predict the mechanical properties of Cu–Al alloys manufactured using the powder metallurgy technique to increase the rate of fabrication and characterization of new materials and provide physical insights into their properties. Six algorithms were used to construct the prediction models, with chemical composition and porosity of the compacts chosen as the descriptors. The results show that the sequential minimal optimization algorithm for support vector regression with a puk kernel (SMOreg/puk) model demonstrated the best prediction ability. Specifically, its predictions exhibited the highest correlation coefficient and lowest error among the predictions of the six models. The SMOreg/puk model was subsequently applied to predict the tensile strength and hardness of Cu–Al alloys and provide guidance for composition design to achieve the expected values. With the guidance of the SMOreg/puk model, Cu–12Al–6Ni alloy with a tensile strength (390 MPa) and hardness (HB 139) that reached the expected values was developed.
Study on the mechanical activation of malachite and the leaching of complex copper ore in the Luanshya mining area, Zambia
Gai-rong Wang, Hong-ying Yang, Yuan-yuan Liu, Lin-lin Tong, and Ali Auwalu
In press, Uncorrected proof  Available online  17 December 2019, https://doi.org/10.1007/s12613-019-1856-z
[Abstract](143) [FullText HTML](0) [PDF 1544KB](9) SpringerLink
Abstract:
Mechanical activation (MA) of malachite was carried out by dry planetary grinding (DPG) and wet Isa grinding (WIG) methods. When the rotational speed was increased to 400 r/min in DPG, the specific surface area of malachite reached the maximum and the particle size reached the minimum of 0.7–100 μm. Agglomeration occurred between mineral particles when the rotational speed was increased to 580 r/min in DPG. However, no agglomeration was observed among particles with sizes 0.4–3 μm in WIG. X-ray diffraction analysis showed that, at a 580 r/min rotational speed in DPG, the amorphization degree of malachite was 53.12%, whereas that in WIG was 71.40%, indicating that MA led to amorphization and distortion of crystal structures. In addition, in the Fourier transform infrared (FT-IR) spectra of activated malachite, the bands associated with –OH, CO32-and metal lattice vibrations of Cu–O and Cu–OH were weakened, and a new H–O–H bending mode and peaks of gaseous CO2 appeared, indicating that MA decreased the band energy, enhanced dihydroxylation, and increased the chemical reactivity of the malachite. Furthermore, the leaching behavior of copper ore was greatly improved by MA.
Strengthening iron enrichment and dephosphorization of high-phosphorus oolitic hematite using high-temperature pretreatment
Wen-tao Zhou, Yue-xin Han, Yong-sheng Sun, and Yan-jun Li
In press, Uncorrected proof  Available online  28 December 2019, https://doi.org/10.1007/s12613-019-1897-3
[Abstract](86) [FullText HTML](0) [PDF 1457KB](1) SpringerLink
Abstract:
The efficient development and utilization of high-phosphorus oolitic hematite is of great strategic significance for the sustainable supply of iron-ore resources in China. In this paper, the mechanism of high-temperature pretreatment for enhancing the effect of iron enrichment and dephosphorization in the magnetization roasting–leaching process was studied by X-ray diffraction (XRD), vibration sample magnetometer (VSM), scanning electron microscopy and energy dispersive spectrometry (SEM-EDS). Compared with the process without high-temperature pretreatment, the iron grade of the magnetic separation concentrate after high-temperature pretreatment had increased by 0.98%, iron recovery rate had increased by 1.33%, and the phosphorus content in the leached residue had decreased by 0.12%. High-temperature pretreatment resulted in the dehydration and decomposition of hydroxyapatite, the dehydration of limonite and the thermal decomposition of siderite, which can produce pores and cracks and weaken the compactness of the ore, improve the magnetization characteristics of roasted ore, and strengthen the iron enrichment and dephosphorization during the magnetization roasting and leaching process.
Controlled synthesis of nanosized Si by magnesiothermic reduction from diatomite as anode material for Li-ion batteries
Li-fen Guo, Shi-yun Zhang, Jian Xie, Dong Zheng, Yuan Jin, Kang-yan Wang, Da-gao Zhuang, Wen-quan Zheng, and Xin-bing Zhao
In press, Uncorrected proof  Available online  19 December 2019, https://doi.org/10.1007/s12613-019-1900-z
[Abstract](176) [FullText HTML](0) [PDF 977KB](9) SpringerLink
Abstract:
Li-ion batteries (LIBs) have demonstrated great promise in electric vehicles and hybrid electric vehicles. However, commercial graphite materials, the current predominant anodes in LIBs, have a low theoretical capacity of only 372 mAh·g−1, which cannot meet the ever-increasing demand of LIBs for high energy density. Nanoscale Si is considered an ideal form of Si for the fabrication of LIB anodes as Si–C composites. Synthesis of nanoscale Si in a facile, cost-effective way, however, still poses a great challenge. In this work, nanoscale Si was prepared by a controlled magnesiothermic reaction using diatomite as the Si source. It was found that the nanoscale Si prepared under optimized conditions (800°C, 10 h) can deliver a high initial specific capacity (3053 mAh·g−1 on discharge, 2519 mAh·g−1 on charge) with a high first coulombic efficiency (82.5%). When using sand-milled diatomite as a precursor, the obtained nanoscale Si exhibited a well-dispersed morphology and had a higher first coulombic efficiency (85.6%). The Si–C (Si:graphite = 1:7 in weight) composite using Si from the sand-milled diatomite demonstrated a high specific capacity (over 700 mAh·g−1 at 100 mA·g−1), good rate capability (587 mAh·g−1 at 500 mA·g−1), and a long life cycle (480 mAh·g−1 after 200 cycles at 500 mA·g−1). This work gives a facile method to synthesize nanoscale Si with both high capacity and high first coulombic efficiency.
The effect of residual structural strain caused by the addition of Co3O4 nanoparticles on the structural, hardness and magnetic properties of an Al/Co3O4 nanocomposite produced by powder metallurgy
Seyed Rahim Kiahosseini and Hossein Ahmadian
In press, Uncorrected proof  Available online  28 October 2019, https://doi.org/10.1007/s12613-019-1917-3
[Abstract](140) [FullText HTML](1) [PDF 915KB](12) SpringerLink
Abstract:
Al composites are of interest due to their appropriate ratio of strength to weight. In our research, an Al/Co3O4 nanocomposite was generated using a sintering technique. The powders of Al with various Co3O4 nanoparticle contents (0wt%, 0.5wt%, 1wt%, 1.5wt%, 2wt%, and 2.5wt%) were first blended using planetary milling for 30 min, and compressed in a cylindrical steel mold with a diameter of 1 cm and a height of 5 cm at a pressure of 80 MPa. The samples were evaluated with X-ray diffractometry (XRD), scanning electron microscopy (SEM), Vickers hardness, and a vibrating sample magnetometer (VSM). Although the crystallite size of the Al particles remained constant at 7–10 nm, the accumulation of nanoparticles in the Al particle interspace increased the structural tensile strain from 0.0045 to 0.0063, the hardness from HV 28 to HV 52 and the magnetic saturation from 0.044 to 0.404 emu/g with an increase in Co3O4 nanoparticle content from 0wt% to 2.5wt%.
Effect of austempering time on microstructure and properties of a low-carbon bainite steel
Man Liu, Guang Xu, Jun-yu Tian, Qing Yuan, and Xin Chen
In press, Uncorrected proof  Available online  12 December 2019, https://doi.org/10.1007/s12613-019-1881-y
[Abstract](109) [FullText HTML](0) [PDF 724KB](8) SpringerLink
Abstract:
The effect of austempering time after the bainitic transformation on the microstructure and property in a low-carbon bainite steel was investigated by metallography and dilatometry. The results showed that by prolonging the austempering time after the bainite transformation, the amount of large-size martensite/austenite islands decreased, but no significant change of the amount and morphology of bainite were observed. In addition, more austenite with a high carbon content was retained by prolonging the holding time at the bainite transformation temperature. Moreover, with a longer holding time, the elongation was improved at the expense of a small decrease in tensile strength. Finally, the Avrami equation BRF = 1− exp(−0.0499 × t0.7616) for bainite reaction at 350°C was obtained for the tested steel. The work provided a reference for tailoring the properties of low-carbon steels.
Effect of cooling temperature on the microstructure and corrosion behavior of X80 pipeline steel
Jing Ma, Fan Feng, Bai-qing Yu, Hai-feng Chen, and Li-feng Fan
In press, Uncorrected proof  Available online  23 December 2019, https://doi.org/10.1007/s12613-019-1882-x
[Abstract](120) [FullText HTML](0) [PDF 1115KB](10) SpringerLink
Abstract:
Dual-phase accelerated cooling (DPAC) was applied to X80 pipeline steel to obtain its microstructure with different amounts of bainite and ferrite. The microstructure, hardness, and polarization behaviors of the steel, cooled to different temperatures, were investigated. Results showed that, with decreasing cooling temperature, the amount of polygon ferrite (PF) increased while that of acicular ferrite (AF) decreased. The amount of bainite correspondingly decreased, except when cooled to 760°C. Moreover, the grain size of ferrite increased. The corrosion behaviors of different phases were distinct. Martensite/austenite (M/A) islands presented at the grain boundary of the PF phase caused small pits. Numerous micro-corrosion cells were formed in the AF and bainite phases, where micropores were prone to form. X80 pipeline steel cooled to 700°C had the best corrosion resistance in the simulated seawater. The decreased amount of the PF phase reduced the area of cathode, resulting in slight corrosion. About 40vol% of the bainite phase provided strength while the PF phase provided adequate ductility to the X80 steel. It was concluded that the appropriate cooling temperature was 700°C for ideal corrosion resistance and mechanical properties.
Effect of gradient temperature rolling process on promoting crack healing in Q500 heavy plates
Zhao-hai Gao, Wei Yu, Xu Chen, Bao-sheng Xie, and Qing-wu Cai
In press, Uncorrected proof  Available online  21 October 2019, https://doi.org/10.1007/s12613-019-1855-0
[Abstract](167) [FullText HTML](1) [PDF 877KB](6) SpringerLink
Abstract:
To ensure the quality of heavy plate products as determined by ultrasonic inspection, it is necessary to effectively control defects such as cracks and shrinkage cavities in heavy plates. Generally, some defects such as large size cracks exist due to insufficient deformation in the center of traditionally rolled plates. Compared with the traditional rolling process, gradient temperature rolling (GTR) process can effectively increase deformation inside heavy plates. In this study, the effect of GTR on crack healing was analyzed through a comparison experiment with the uniform temperature rolling (UTR). The results show that the GTR process could increase the plastic strain inside the heavy plate and effectively promote the healing process of the preset cracks. The degrees of crack healing at the center and quarter thickness position of the steel plate via GTR were greater than twice those of the plate via UTR. The GTR process can significantly reduce the internal defects of heavy plates and improve the defect detection level of heavy plate products. Also, The GTR process results in the formation of new crystal grains in the crack region, which is crucial to crack healing.
Influence of TiO2 on the melting property and viscosity of Cr-containing high-Ti melting slag
Jing Ma, Gui-qin Fu, Wei Li, and Miao-yong Zhu
In press, Corrected proof  Available online  12 December 2019, https://doi.org/10.1007/s12613-019-1914-6
[Abstract](137) [FullText HTML](1) [PDF 876KB](14) SpringerLink
Abstract:
A study on the melting and viscosity properties of the chromium-containing high-titanium melting slag (CaO–SiO2–MgO–Al2O3–TiO2–Cr2O3) with TiO2 contents ranging from 38.63wt% to 42.63wt% was conducted. The melting properties were investigated with a melting-point apparatus, and viscosity was measured using the rotating cylinder method. The FactSage 7.1 software and X-ray diffraction, in combination with scanning electron microscopy–energy-dispersive spectroscopy (SEM–EDS), were used to characterize the phase equilibrium and microstructure of chromium-containing high-titanium melting slags. The results indicated that an increase in the TiO2 content led to a decrease in the viscosity of the chromium-containing high-titanium melting slag. In addition, the softening temperature, hemispheric temperature, and flowing temperature decreased with increasing TiO2 content. The amount of crystallized anosovite and sphene phases gradually increased with increasing TiO2 content, whereas the amount of perovskite phase decreased. SEM observations revealed that the distribution of the anosovite phase was dominantly influenced by TiO2.
Effects of calcium compounds on the carbothermic reduction of vanadium titanomagnetite concentrate
Xiao-hui Li, Jue Kou, Ti-chang Sun, Shi-chao Wu, and Yong-qiang Zhao
In press, Corrected proof  Available online  9 December 2019, https://doi.org/10.1007/s12613-019-1864-z
[Abstract](123) [FullText HTML](0) [PDF 1766KB](6) SpringerLink
Abstract:
Effects of calcium compounds on the carbothermic reduction of vanadium titanomagnetite concentrate (VTC) were investigated. It was found that calcium compounds had great effects on the metallization rate of the reduction product, the order of the metallization rate of reduction product being CaCO3 > no additive > CaSO4 > CaCl2, which indicated that the addition of CaCO3 was more conducive to promoting the reduction of iron than other calcium compounds. Gas analysis showed that there were mainly two processes in the carbothermic reduction of VTC, a solid–solid and a solid–gas reaction. The concentrations of CO and CO2 were highest when CaCO3 was added, while that in a roasting system decreased the most when CaCl2 was added. X-ray diffraction (XRD) analysis showed that calcium compounds could change the reduction process of ilmenite in VTC. The phase compositions of the reduction products were changed from metallic iron (Fe) and anosovite (FeTi2O5) to metallic iron (Fe) and perovekite (CaTiO3) when calcium compounds were added. Additionally, CaSO4 and CaCl2 could significantly promote the growth of metallic iron particles, though the existence of Fe-bearing Mg2TiO4 in reduction products was not conducive to the reduction of iron. The formation of FeS would further hinder the reduction of iron after adding CaSO4.
Nd–Mg–Ni alloy electrodes modified by reduced graphene oxide with improved electrochemical kinetics
Yuan Li, Li-na Cheng, Wen-kang Miao, Chun-xiao Wang, De-zhi Kuang, and Shu-min Han
In press, Corrected proof  Available online  17 December 2019, https://doi.org/10.1007/s12613-019-1880-z
[Abstract](107) [FullText HTML](0) [PDF 871KB](2) SpringerLink
Abstract:
To improve the electrochemical kinetics of Nd–Mg–Ni alloy electrodes, the alloy surface was modified with highly conductive reduced graphene oxide (rGO) via a chemical reduction process. Results indicated that rGO sheets uniformly coated on the alloy surface, yielding a three-dimensional network layer. The coated surfaces contained numerous hydrophilic functional groups, leading to better wettability of the alloy in aqueous alkaline media. This, in turn, increased the concentration of electro-active species at the interface between the electrode and the electrolyte, improving the electrochemical kinetics and the rate discharge of the electrodes. The high rate dischargeability at 1500 mA·g–1 increased from 53.2% to 83.9% after modification. In addition, the modification layer remained stable and introduced a dense metal oxide layer to the alloy surface after a long cycling process. Therefore, the protective layer prevented the discharge capacity from quickly decreasing and improved cycling stability.
A mathematical model for column leaching of ion adsorption-type rare earth ores
Ping Long, Guan-shi Wang, Shuo Zhang, Shi-li Hu, and Ying Huang
In press, Corrected proof  Available online  14 December 2019, https://doi.org/10.1007/s12613-019-1883-9
[Abstract](111) [FullText HTML](0) [PDF 822KB](13) SpringerLink
Abstract:
Column leaching experiments with ion adsorption-type rare earth ores for different lixiviant concentrations and different column heights were carried out. A mathematical model of column leaching was constructed based on the experimental data. Two parameters (a and b) in the model were determined according to the following methodology: the ore column was divided into several units; each unit was treated with multiple leaching steps. The leaching process was simulated as a series of batch leaching experiments. Parameter a of the model was determined based on the selectivity coefficient of the balanced batch leaching experiment. Further, the influences of ammonium sulfate concentration, rare earth grade, column height, permeability coefficient, and hydrodynamic dispersion coefficient on the extraction were analyzed. Relationships between parameter b, the ammonium sulfate concentration, and the physical and mechanical properties of the ore column, were examined using dimensional analysis. It was determined that the optimal ammonium sulfate concentration for different column heights (2.5, 5.0, 7.5, and 10.0 cm) using the mathematical model were 5.9, 6.2, 7.3, and 7.7 g/L, respectively. The mathematical model can be used to estimate the breakthrough curve, leaching rate, and leaching period of rare earth ores, to achieve optimal extraction.
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Invited Review
Big data management in the mining industry
Chong-chong Qi
2020, vol. 27, no. 2, pp. 131-139. https://doi.org/10.1007/s12613-019-1937-z
[Abstract](211) [FullText HTML](0) [PDF 659KB](20) SpringerLink
Abstract:
The mining industry faces a number of challenges that promote the adoption of new technologies. Big data, which is driven by the accelerating progress of information and communication technology, is one of the promising technologies that can reshape the entire mining landscape. Despite numerous attempts to apply big data in the mining industry, fundamental problems of big data, especially big data management (BDM), in the mining industry persist. This paper aims to fill the gap by presenting the basics of BDM. This work provides a brief introduction to big data and BDM, and it discusses the challenges encountered by the mining industry to indicate the necessity of implementing big data. It also summarizes data sources in the mining industry and presents the potential benefits of big data to the mining industry. This work also envisions a future in which a global database project is established and big data is used together with other technologies (i.e., automation), supported by government policies and following international standards. This paper also outlines the precautions for the utilization of BDM in the mining industry.
Research Article
Long-term mechanical behavior and characteristics of cemented tailings backfill through impact loading
Yu-ye Tan, Elmo Davide, Yu-cheng Zhou, Wei-dong Song, and Xiang Meng
2020, vol. 27, no. 2, pp. 140-151. https://doi.org/10.1007/s12613-019-1878-6
[Abstract](147) [FullText HTML](0) [PDF 5470KB](14) SpringerLink
Abstract:
Cemented tailings backfill (CTB) structures are important components of underground mine stopes. It is important to investigate the characteristics and dynamic behavior of CTB materials because they are susceptible to disturbance by dynamic loading, such as excavation and blasting. In this study, the authors present the results of a series of Split–Hopkinson pressure bar (SHPB) single and cyclic impact loading tests on CTB specimens to investigate the long-term dynamic mechanical properties of CTB. The stress–strain relationship, dynamic strength, and dynamic failure characteristics of CTB specimens are analyzed and discussed to provide valuable conclusions that will improve our knowledge of CTB long-term mechanical behavior and characteristics. For instance, the dynamic peak stress under cyclic impact loading is approximately twice that under single impact loading, and the CTB specimens are less prone to fracture when cyclically loaded. These findings and conclusions can provide a new set of references for the stability analysis of CTB materials and help guide mine designers in reducing the amount of binding agents and the associated mining cost.
An experimental study on size distribution and zeta potential of bulk cavitation nanobubbles
Xu-yu Zhang, Qian-shuai Wang, Zhong-xian Wu, and Dong-ping Tao
2020, vol. 27, no. 2, pp. 152-161. https://doi.org/10.1007/s12613-019-1936-0
[Abstract](296) [FullText HTML](1) [PDF 679KB](34) SpringerLink
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Nanobubble flotation technology is an important research topic in the field of fine mineral particle separation. The basic characteristics of nanobubbles, including their size, concentration, surface zeta potential, and stability have a significant impact on the nanobubble flotation performance. In this paper, bulk nanobubbles generated based on the principle of hydrodynamic cavitation were investigated to determine the effects of different parameters (e.g., surfactant (frother) dosage, air flow, air pressure, liquid flow rate, and solution pH value) on their size distribution and zeta potential, as measured using a nanoparticle analyzer. The results demonstrated that the nanobubble size decreased with increasing pH value, surfactant concentration, and cavitation-tube liquid flow rate but increased with increasing air pressure and increasing air flow rate. The magnitude of the negative surface charge of the nanobubbles was positively correlated with the pH value, and a certain relationship was observed between the zeta potential of the nanobubbles and their size. The structural parameters of the cavitation tube also strongly affected the characteristics of the nanobubbles. The results of this study offer certain guidance for optimizing the nanobubble flotation technology.
Insight into the change in carbon structure and thermodynamics during anthracite transformation into graphite
Tian Qiu, Jian-guo Yang, and Xue-jie Bai
2020, vol. 27, no. 2, pp. 162-172. https://doi.org/10.1007/s12613-019-1859-9
[Abstract](104) [FullText HTML](0) [PDF 1267KB](5) SpringerLink
Abstract:
The thermodynamic and kinetic mechanisms of Taixi anthracite during its graphitization process were explored. To understand the variation trends of carbon arrangement order, microcrystal size, and graphitization degree against temperature during the graphitization process, a series of experiments were performed using Raman spectroscopy and X-ray diffraction (XRD). Subsequently, the influencing factors of the dominant reaction at different temperatures were analyzed using thermodynamics and kinetics. The results showed that the graphitization process of Taixi anthracite can be divided into three stages from the perspective of reaction thermodynamics and kinetics. Temperature played a crucial role in the formation and growth of a graphitic structure. Meanwhile, multivariate mechanisms coexisted in the graphitization process. At ultrahigh temperatures, the defects of synthetic graphite could not be completely eliminated and perfect graphite crystals could not be produced. At low temperatures, the reaction is mainly controlled by dynamics, while at high temperatures, thermodynamics dominates the direction of the reaction.
Characteristics of a coherent jet enshrouded in a supersonic fuel gas
Fei Zhao, Rong Zhu, and Wen-rui Wang
2020, vol. 27, no. 2, pp. 173-180. https://doi.org/10.1007/s12613-019-1928-0
[Abstract](150) [FullText HTML](1) [PDF 990KB](7) SpringerLink
Abstract:
Based on a current coherent jet, this study proposes a supersonic combustion (SC) coherent jet in which the main oxygen jet is surrounded by a supersonic fuel gas. The characteristics of the proposed coherent jet are analyzed using experimental methods and numerical simulations in the high-temperature environment of electric arc furnace (EAF) steelmaking. The SC coherent jet achieved stable combustion in the EAF steelmaking environment. The simulated combustion temperature of the supersonic shrouding methane gas was 2930 K, slightly below the theoretical combustion temperature of methane–oxygen gas. The high speed and temperature of the supersonic flame effectively weakened the interaction between the main oxygen jet and the external ambient gas, inhibiting the radial expansion of the main oxygen jet and maintaining its high speed and low turbulence over a long distance. These features improved the impact capacity of the coherent jet and strengthened the stirring intensity in the EAF bath.
Co-oxidation of arsenic(III) and iron(II) ions by pressurized oxygen in acidic solutions
Ke-zhou Song, Ping-chao Ke, Zhi-yong Liu, and Zhi-hong Liu
2020, vol. 27, no. 2, pp. 181-189. https://doi.org/10.1007/s12613-019-1786-9
[Abstract](235) [FullText HTML](3) [PDF 598KB](11) SpringerLink
Abstract:
The co-oxidation of As(III) and Fe(II) in acidic solutions by pressured oxygen was studied under an oxygen pressure between 0.5 and 2.0 MPa at a temperature of 150°C. It was confirmed that without Fe(II) ions, As(III) ions in the solutions are virtually non-oxidizable by pressured oxygen even at a temperature as high as 200°C and an oxygen pressure up to 2.0 MPa. Fe(II) ions in the solutions did have a catalysis effect on the oxidation of As(III), possibly attributable to the production of such strong oxidants as hydroxyl free radicals (OH·) and Fe(IV) in the oxidation process of Fe(II). The effects of such factors as the initial molar ratio of Fe(II)/As(III), initial pH value of the solution, oxygen pressure, and the addition of radical scavengers on the oxidation efficiencies of As(III) and Fe(II) were studied. It was found that the oxidation of As(III) was limited in the co-oxidation process due to the accumulation of the As(III) oxidation product, As(V), in the solutions.
Thermal and microstructural characterization of a novel ductile cast iron modified by aluminum addition
Gülşah Aktaş Çelik, Maria-Ioanna T. Tzini, Şeyda Polat, Ş. Hakan Atapek, and Gregory N. Haidemenopoulos
2020, vol. 27, no. 2, pp. 190-199. https://doi.org/10.1007/s12613-019-1876-8
[Abstract](221) [FullText HTML](0) [PDF 1013KB](45) SpringerLink
Abstract:
In high-temperature applications, like exhaust manifolds, cast irons with a ferritic matrix are mostly used. However, the increasing demand for higher-temperature applications has led manufacturers to use additional expensive materials such as stainless steels and Ni-resist austenitic ductile cast irons. Thus, in order to meet the demand while using low-cost materials, new alloys with improved high-temperature strength and oxidation resistance must be developed. In this study, thermodynamic calculations with Thermo-Calc software were applied to study a novel ductile cast iron with a composition of 3.5wt% C, 4wt% Si, 1wt% Nb, 0‒4wt% Al. The designed compositions were cast, and thermal analysis and microstructural characterization were performed to validate the calculations. The lowest critical temperature of austenite to pearlite eutectoid transformation, i.e., A1, was calculated, and the solidification sequence was determined. Both calculations and experimental data revealed the importance of aluminum addition, as the A1 increased by increasing the aluminum content in the alloys, indicating the possibility of utilizing the alloys at higher temperature. The experimental data validated the transformation temperature during solidification and at the solid state and confirmed the equilibrium phases at room temperature as ferrite, graphite, and MC-type carbides.
Simulation of macrosegregation in a 36-t steel ingot using a multiphase model
Zhuo Chen and Hou-fa Shen
2020, vol. 27, no. 2, pp. 200-209. https://doi.org/10.1007/s12613-019-1875-9
[Abstract](102) [FullText HTML](0) [PDF 14142KB](8) SpringerLink
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Macrosegregation is the major defect in large steel ingots caused by solute partitioning and melt convection during casting. In this study, a three-phase (liquid, columnar dendrites, and equiaxed grains) model is proposed to simulate macrosegregation in a 36-t steel ingot. A supplementary set of conservation equations are employed in the model such that two types of equiaxed grains, either settling or adhering to the solid shell, are well simulated. The predicted concentration agrees quantitatively with the experimental value. A negative segregation cone was located at the bottom owing to the grain settlement and solute-enriched melt leaving from the mushy zone. The interdendritic liquid flow was carefully analyzed, and the formation of A-type segregations in the mid-height of the ingot is discussed. Negative segregation was observed near the riser neck due to the specific relationship between flow direction and temperature gradient. Additionally, the as-cast macrostructure of the ingot is presented, including the grain size distribution and columnar–equiaxed transition.
Effect of plastic strain and forming temperature on magnetic properties of low-carbon steel
Fan Zeng, Xue-jiao Bai, Cheng-liang Hu, Min-jun Tang, and Zhen Zhao
2020, vol. 27, no. 2, pp. 210-219. https://doi.org/10.1007/s12613-019-1905-7
[Abstract](107) [FullText HTML](1) [PDF 827KB](4) SpringerLink
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Claw poles are a key component of automobile generators. The output power performance of the generator is very dependent on the magnetic properties of its claw poles. Plastic deformation is known to significantly change the magnetic behavior of ferromagnetic materials in claw poles. In this paper, changes in the magnetic properties of low-carbon steel, used for claw pole components due to their plastic deformation, were investigated for different strains and temperatures. Ring-shaped material samples were prepared by machining and their magnetic properties were measured. The surface roughness was first evaluated and a machining process with an arithmetic average of roughness Ra 1.6 μm was selected as enabling the lowest measurement error. Hysteresis loops at different applied magnetic fields of the material were obtained for different plastic strains and forming temperatures. The magnetic parameters of magnetic flux density, coercivity, and remanence were obtained and compared with magnetic flux density as the primary focus. Results showed that machining, cold forming, and hot forming all led to lower magnetic flux density, larger coercivity, and smaller remanence. Magnetic flux density showed a sharp decrease at the start of plastic deformation, but as the strain increased, the decreasing trend gradually reached a constant value. The decrease was much larger for cold forming than for hot forming. For example, at 500 A/m, the degradation of magnetic flux density with a reduction percentage of 5% at room temperature was about 50%, while that of hot forming at 1200°C was about 10%. Results of this research may provide a reference for the future process design of hot-forged claw poles.
Supercapacitor electrode based on few-layer h-BNNSs/rGO composite for wide-temperature-range operation with robust stable cycling performance
Tao Yang, Hui-juan Liu, Fan Bai, En-hui Wang, Jun-hong Chen, Kuo-Chih Chou, and Xin-mei Hou
2020, vol. 27, no. 2, pp. 220-231. https://doi.org/10.1007/s12613-019-1910-x
[Abstract](155) [FullText HTML](0) [PDF 1022KB](6) SpringerLink
Abstract:
Currently, developing supercapacitors with robust cycle stability and suitability for wide-temperature-range operations is still a huge challenge. In the present work, few-layer hexagonal boron nitride nanosheets (h-BNNSs) with a thickness of 2−4 atomic layers were fabricated via vacuum freeze-drying and nitridation. Then, the h-BNNSs/reduced graphene oxide (rGO) composite were further prepared using a hydrothermal method. Due to the combination of two two-dimensional (2D) van der Waals-bonded materials, the as-prepared h-BNNSs/rGO electrode exhibited robustness to wide-temperature-range operations from −10 to 50°C. When the electrodes worked in a neutral aqueous electrolyte (1 M Na2SO4), they showed a great stable cycling performance with almost 107% reservation of the initial capacitance at 0°C and 111% at 50°C for 5000 charge−discharge cycles.
Effect of sintering temperature on pore ratio and mechanical properties of composite structure in nano graphene reinforced ZA27 based composites
Muharrem Pul
2020, vol. 27, no. 2, pp. 232-243. https://doi.org/10.1007/s12613-019-1926-2
[Abstract](147) [FullText HTML](0) [PDF 1138KB](11) SpringerLink
Abstract:
Nano graphene platelet (Gr) reinforced nano composites with a zinc–aluminum alloy (ZA27) matrix were produced by powder metallurgy at four different mass ratios (0.5wt%, 1.0wt%, 2.0wt% and 4.0wt%) and three different sintering temperatures (425, 450, and 475°C). In order to investigate the effect of sintering temperatures and nano graphene reinforcement materials on the composite structure, the microstructures of the composite samples were investigated and their densities were determined with a scanning electron microscope. Hardness, transverse rupture, and abrasion wear tests were performed to determine the mechanical properties. According to the test results, the porosity increased and the mechanical strength of the nano composites decreased as the amount of nano graphene reinforcement in ZA27 increased. However, when the composites produced in different reinforcement ratios were evaluated, the increase in sintering temperature increased the mechanical structure by positively affecting the composite structure.
Preparation of WC/CoCrFeNiAl0.2 high-entropy-alloy composites by high-gravity combustion synthesis
Guan-nan Zhang, Xiao Yang, Zeng-chao Yang, Yong Li, Gang He, and Jiang-tao Li
2020, vol. 27, no. 2, pp. 244-251. https://doi.org/10.1007/s12613-019-1892-8
[Abstract](166) [FullText HTML](0) [PDF 2265KB](18) SpringerLink
Abstract:
The WC/CoCrFeNiAl0.2 high-entropy alloy (HEA) composites were prepared through high-gravity combustion synthesis. The preparation method is presented below. First, using a designed suitable multiphase thermite system, the molten CoCrFeNiAl0.2 HEA was fabricated using low-cost metal oxides. The molten HEA was subsequently infiltrated into the WC layer to fabricate WC/CoCrFeNiAl0.2 composites in a high-gravity field. The porosity of the WC/CoCrFeNiAl0.2 composites was down-regulated, and their compressive yield strength was up-regulated when the high-gravity field was increased from 600g to 1500g because this infiltration process of a HEA melt into the WC layer is driven by centrifugal force. The WC particles in the composites exhibited a gradient distribution along the direction of the centrifugal force, which was attributed to the combined action of the high-gravity field and the temperature gradient field. The Vickers hardness of the sample was down-regulated from 9.53 to 7.41 GPa along the direction of the centrifugal force.
Mechanical characterization of Mg−B4C nanocomposite fabricated at different strain rates
Gholam Hossein Majzoobi and Kaveh Rahmani
2020, vol. 27, no. 2, pp. 252-263. https://doi.org/10.1007/s12613-019-1902-x
[Abstract](66) [FullText HTML](0) [PDF 2380KB](2) SpringerLink
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Magnesium has wide application in industry. The main purpose of this investigation was to improve the properties of magnesium by reinforcing it using B4C nanoparticles. The reinforced nanocomposites were fabricated using a powder compaction technique for 0, 1.5vol%, 3vol%, 5vol%, and 10vol% of B4C. Powder compaction was conducted using a split Hopkinson bar (SHB), drop hammer (DH), and Instron to reach different compaction loading rates. The compressive stress–strain curves of the samples were captured from quasi-static and dynamic tests carried out using an Instron and split Hopkinson pressure bar, respectively. Results revealed that, to achieve the highest improvement in ultimate strength, the contents of B4C were 1.5vol%, 3vol%, and 3vol% for Instron, DH, and SHB, respectively. These results also indicated that the effect of compaction type on the quasi-static strength of the samples was not as significant, although its effect on the dynamic strength of the samples was remarkable. The improvement in ultimate strength obtained from the quasi-static stress–strain curves of the samples (compared to pure Mg) varied from 9.9% for DH to 24% for SHB. The dynamic strength of the samples was improved (with respect to pure Mg) by 73%, 116%, and 141% for the specimens compacted by Instron, DH, and SHB, respectively. The improvement in strength was believed to be due to strengthening mechanisms, friction, adiabatic heating, and shock waves.
Electrochemical behavior and corrosion resistance of IrO2–ZrO2 binary oxide coatings for promoting oxygen evolution in sulfuric acid solution
Bao Liu, Shuo Wang, Cheng-yan Wang, Bao-zhong Ma, and Yong-qiang Chen
2020, vol. 27, no. 2, pp. 264-273. https://doi.org/10.1007/s12613-019-1847-0
[Abstract](174) [FullText HTML](0) [PDF 1060KB](5) SpringerLink
Abstract:
In this study, we prepared Ti/IrO2–ZrO2 electrodes with different ZrO2 contents using zirconium-n-butoxide (C16H36O4Zr) and chloroiridic acid (H2IrCl6) via a sol–gel route. To explore the effect of ZrO2 content on the surface properties and electrochemical behavior of electrodes, we performed physical characterizations and electrochemical measurements. The obtained results revealed that the binary oxide coating was composed of rutile IrO2, amorphous ZrO2, and an IrO2–ZrO2 solid solution. The IrO2–ZrO2 binary oxide coatings exhibited cracked structures with flat regions. A slight incorporation of ZrO2 promoted the crystallization of the active component IrO2. However, the crystallization of IrO2 was hindered when the added ZrO2 content was greater than 30at%. The appropriate incorporation of ZrO2 enhanced the electrocatalytic performance of the pure IrO2 coating. The Ti/70at%IrO2–30at%ZrO2 electrode, with its large active surface area, improved electrocatalytic activity, long service lifetime, and especially, lower cost, is the most effective for promoting oxygen evolution in sulfuric acid solution.