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Invited Review
Application of low-cost particulate matter sensors for air quality monitoring and exposure assessment in underground mines: A review
Nana A. Amoah, Guang Xu, Yang Wang, Jiayu Li, Yongming Zou, and  Baisheng Nie
2022, vol. 29, no. 8, pp. 1475-1490. https://doi.org/10.1007/s12613-021-2378-z
Abstract:
Exposure to mining-induced particulate matter (PM) including coal dust and diesel particulate matter (DPM) causes severe respiratory diseases such as coal workers’ pneumoconiosis (CWP) and lung cancer. Limited spatiotemporal resolution of current PM monitors causes miners to be exposed to unknown PM concentrations, with increased overexposure risk. Low-cost PM sensors offer a potential solution to this challenge with their capability in characterizing PM concentrations with high spatiotemporal resolution. However, their application in underground mines has not been explored. With the aim of examining the potential application of low-cost sensors in underground mines, a critical review of the present status of PM sensor research is conducted. The working principles of present PM monitors and low-cost sensors are compared. Sensor error sources are identified, and comprehensive calibration processes are presented to correct them. Evaluation protocols are proposed to evaluate sensor performance prior to deployment, and the potential application of low-cost sensors is discussed.
Highlight
Omnidirectional annealing process for scalable perovskite films
Bo Cheng, Dong Wang, Qianqian Chu, and  Liang Chu
2022, vol. 29, no. 8, pp. 1491-1492. https://doi.org/10.1007/s12613-021-2405-0
Abstract:
Halide perovskites are promising photovoltaic materials due to the outstanding photoelectric properties and low-cost solution process; however, the low scalability and reproducibility of perovskite films hinder the commercialization. Liquid medium annealing (LMA) method has provided a robust liquid environment and an omnidirectional heating field to modulate the growth of perovskite films for high quality with low defect density, desirable stoichiometry, high homogeneity, and less environmental influence. The fabricated perovskite solar cells exhibited excellent reproducibility and power conversion efficiencies exceeding 24.04% with 0.08 cm2 area and 23.15% with 1 cm2 area.
Research Article
Surface nanobubbles on the hydrophobic surface and their implication to flotation
Chenwei Li, Danlong Li, Xin Li, Ming Xu, and  Haijun Zhang
2022, vol. 29, no. 8, pp. 1493-1501. https://doi.org/10.1007/s12613-021-2279-1
Abstract:
Nanobubbles play a potential role in the application of the flotation of fine particles. In this work, the identification of nanoentities was performed with a contact mode atomic force microscope (AFM). Moreover, the influences of setpoint ratio and amplitude of the cantilever and the responses of the formed surface nanobubbles to the fluctuation of pH, salt concentration, and surfactant concentration in the slurry were respectively studied. Nanobubbles were reported on the highly oriented pyrolytic graphite (HOPG) surface as the HOPG was immersed in deionized water under ambient temperature. The coalescence of nanobubbles occurred under contact mode, which provides strong evidence of the gaseous nature of these nanostructures on HOPG. The measuring height of the surface nanobubbles decreased with the setpoint ratio. The changes in the pH and concentration of methyl isobutyl carbinol (MIBC) show a negligible influence on the lateral size and height of the preexisting surface nanobubbles. The addition of LiCl results in a negligible change of the lateral size; however, an obvious change is noticed in the height of surface nanobubbles. The results are expected to provide a valuable reference in understanding the properties of surface nanobubbles and in the design of nanobubble-assisted flotation processes.
Research Article
Flotation kinetics performance of different coal size fractions with nanobubbles
Hua Han, An Liu, Caili Wang, Runquan Yang, Shuai Li, and  Huaifa Wang
2022, vol. 29, no. 8, pp. 1502-1510. https://doi.org/10.1007/s12613-021-2280-8
Abstract:
The flotation kinetics of different size fractions of conventional and nanobubble (NB) flotation were compared to investigate the effect of NBs on the flotation performance of various coal particle sizes. Six flotation kinetics models were selected to fit the flotation data, and NBs were observed on a hydrophobic surface under hydrodynamic cavitation by atomic force microscope scanning. Flotation results indicated that the best flotation performance of size fraction at −0.125+0.074 mm can be obtained either in conventional or NB flotation. NBs increase the combustible recovery of almost all the size fractions, but they increase the product ash content of −0.25+0.074 mm and reduce the product ash content of −0.045 mm at the same time. The first-order models can be used to fit the flotation data in conventional and NB flotation, and the classical first-order model is the most suitable one. NBs considerably enhance flotation rate on coarse size fraction (−0.5+0.25 mm) but decrease the flotation rate of the medium size (−0.25+0.074 mm). The improvement of flotation speed on fine coal particles (−0.074 mm) is probably the reason for the improved performance of raw sample flotation.
Research Article
Effect of an external magnetic field on improved electroslag remelting cladding process
Zhiwen Hou, Yanwu Dong, Zhouhua Jiang, Zhihao Hu, Limeng Liu, and  Kunjie Tian
2022, vol. 29, no. 8, pp. 1511-1521. https://doi.org/10.1007/s12613-021-2277-3
Abstract:
Obtaining a uniform interface temperature field plays a crucial role in the interface bonding quality of bimetal compound rolls. Therefore, this study proposes an improved electroslag remelting cladding (ESRC) process using an external magnetic field to improve the uniformity of the interface temperature of compound rolls. The improved ESRC comprises a conventional ESRC circuit and an external coil circuit. A comprehensive 3D model, including multi-physics fields, is proposed to study the effect of external magnetic fields on the multi-physics fields and interface temperature uniformity. The simulated results demonstrate that the non-uniform Joule heat and flow fields cause a non-uniform interface temperature in the conventional ESRC. As for the improved ESRC, the magnetic flux density ( B coil) along the z-axis is produced by an anticlockwise current of the external coil. The rotating Lorentz force is generated from the interaction between the radial current and axial B coil. Therefore, the slag pool flows clockwise, which enhances circumferential effective thermal conductivity. As a result, the uniformity of the temperature field and interface temperature improve. In addition, the magnetic flux density and rotational speed of the simulated results are in good agreement with those of the experimental results, which verifies the accuracy of the improved ESRC model. Therefore, an improved ESRC is efficient for industrial production of the compound roll with a uniform interface bonding quality.
Research Article
Effect of Al2O3 content on the viscosity and structure of CaO–SiO2–Cr2O3–Al2O3 slags
Fang Yuan, Zheng Zhao, Yanling Zhang, and  Tuo Wu
2022, vol. 29, no. 8, pp. 1522-1531. https://doi.org/10.1007/s12613-021-2306-2
Abstract:
The effect of Al2O3 content on the viscosity and structure of CaO–SiO2–Cr2O3–Al2O3 slags was investigated to facilitate recycling of Cr in steelmaking slags. The slags exhibit good Newtonian behavior at high temperature. The viscosity of acidic slag first increases from 0.825 to 1.141 Pa·s as the Al2O3 content increases from 0 to 10wt% and then decreases to 1.071 Pa·s as the Al2O3 content increases further to 15wt%. The viscosity of basic slag first increases from 0.084 to 0.158 Pa·s as the Al2O3 content increases from 0 to 15wt% and then decreases to 0.135 Pa·s as the Al2O3 content increases further to 20wt%. Furthermore, Cr2O3-containing slag requires less Al2O3 to reach the maximum viscosity than Cr2O3-free slag; the Al2O3 contents at which the behavior changes are 10wt% and 15wt% for acidic and basic slags, respectively. The activation energy of the slags is consistent with the viscosity results. Raman spectra demonstrate that [AlO4] tetrahedra appear initially and were replaced by [AlO6] octahedra with further addition of Al2O3. The dissolved organic phosphorus content of the slag first increases and then decreases with increasing Al2O3 content, which is consistent with the viscosity and Raman results.
Research Article
Effect of crystallographic orientation on crack growth behaviour of HSLA steel
Endian Fan, Yong Li, Yang You, and  Xuewei Lü
2022, vol. 29, no. 8, pp. 1532-1542. https://doi.org/10.1007/s12613-022-2415-6
Abstract:
In this work, the crack growth behaviours of high strength low alloy (HSLA) steel E690 with three crystallographic orientations (the rolling direction, normal direction, and transverse direction) were investigated and compared from the view of the mechano-electrochemical effect at the crack tip. The results show that the crack growth of the HSLA steel is controlled by the corrosion fracture at the crack tip. The variation of crystallographic orientation in E690 steel plate has no influence on the crack tip electrochemical reaction and crack growth mechanism, but changes the crack growth rate. When the stress loading direction is parallel to the rolling direction and the fracture layer is parallel to the transverse-normal plane, the crack growth rate is the slowest with a value of 0.0185 mm·h–1. When the load direction and the fracture layer are parallel to the normal direction and the rolling-transverse plane, respectively, the crack growth rate is the highest with a value of 0.0309 mm·h–1. This phenomenon is ascribed to the different microstructural and mechanical properties in the rolling direction, normal direction, and transverse direction of E690 steel plate.
Research Article
Icosahedral quasicrystal structure of the Mg40Zn55Nd5 phase and its thermodynamic stability
Shuai Zhang, Qianqian Li, Hongcan Chen, Qun Luo, and  Qian Li
2022, vol. 29, no. 8, pp. 1543-1550. https://doi.org/10.1007/s12613-021-2391-2
Abstract:
The quasicrystal phase is beneficial to increasing the strength of magnesium alloys. However, its complicated structure and unclear phase relations impede the design of alloys with good mechanical properties. In this paper, the Mg40Zn55Nd5 icosahedral quasicrystal (I-phase) structure is discovered in an as-cast Mg–58Zn–4Nd alloy by atomic resolution high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). A cloud-like morphology is observed with Mg41.6Zn55.0Nd3.4 composition. The selected area electronic diffraction (SAED) analysis shows that the icosahedral quasicrystal structure has 5-fold, 4-fold, 3-fold, and 2-fold symmetry zone axes. The thermodynamic stability of the icosahedral quasicrystal is investigated by differential scanning calorimetry (DSC) in the annealed alloys. When annealed above 300°C, the Mg40Zn55Nd5 quasicrystal is found to decompose into a stable ternary phase Mg35Zn60Nd5, a binary phase MgZn, and α-Mg, suggesting that the quasicrystal is a metastable phase in the Mg–Zn–Nd system.
Research Article
Simultaneously improving mechanical properties and corrosion resistance of as-cast AZ91 Mg alloy by ultrasonic surface rolling
Jing Han, Cong Wang, Yuanming Song, Zhiyuan Liu, Jiapeng Sun, and  Jiyun Zhao
2022, vol. 29, no. 8, pp. 1551-1558. https://doi.org/10.1007/s12613-021-2294-2
Abstract:
Mg alloy casting parts commonly suffer from drawbacks of low surface properties, high susceptibility to corrosion, unsatisfactory absolute strength, and poor ductility, which seriously limit their wide application. Here, a surface nanocrystallization technique, i.e., ultrasonic surface rolling (USR), was applied on an as-cast AZ91 Mg alloy sheet to improve its corrosion resistance and mechanical properties. The USR produces double smooth surfaces with Ra 0.036 μm and gradient nanostructured surface layers on the sheet. Due to this special microstructure modification, the USR sheet exhibits 55% and 50% improvements in yield strength and ultimate tensile strength without visibly sacrificed ductility comparable to its untreated counterpart, as well as a 24% improvement in surface hardness. The USR sheet also shows good corrosion resistance in 3.5wt% NaCl aqueous solution. The corrosion current density of the USR sheet reduces by 63% after immersion for 1 h, and 25% after immersion for 24 h compared to that of the untreated counterpart. The enhanced strength and hardness are mainly related to the gradient nanostructure. The improved corrosion resistance is mainly ascribed to the decreased surface roughness, nanostructured surface, and residual compressive stress. The present results state that USR is an effective and attractive method to improve the multiple properties of Mg alloy casting parts, and thus can be used as an additional and last working procedure to achieve high-performance Mg alloy casting parts.
Research Article
Role of trace additions of Ca and Sn in improving the corrosion resistance of Mg–3Al–1Zn alloy
Panpan Wang, Haitao Jiang, Yujiao Wang, Yun Zhang, Shiwei Tian, Yefei Zhang, and  Zhiming Cao
2022, vol. 29, no. 8, pp. 1559-1569. https://doi.org/10.1007/s12613-021-2268-4
Abstract:
The limited wide applicability of commercial Mg alloys is mainly attributed to the poor corrosion resistance. Addition of alloying elements is the simplest and effective method to improve the corrosion properties. Based on the low-cost alloy composition design, the corrosion behavior of commercial Mg–3Al–1Zn (AZ31) alloy bearing minor Ca or Sn element was characterized by scanning Kelvin probe force microscopy, hydrogen evolution, electrochemical measurements, and corrosion morphology analysis. Results revealed that the potential difference of Al2Ca/α-Mg and Mg2Sn/α-Mg was (230 ± 19) mV and (80 ± 6) mV, respectively, much lower than that of Al8Mn5/α-Mg (430 ± 31) mV in AZ31 alloy, which illustrated that AZ31–0.2Sn alloy performed the best corrosion resistance, followed by AZ31–0.2Ca, while AZ31 alloy exhibited the worst corrosion resistance. Moreover, Sn dissolved into matrix obviously increased the potential of α-Mg and participated in the formation of dense SnO2 film at the interface of matrix, while Ca element was enriched in the corrosion product layer, resulting in the corrosion product layer of AZ31–0.2Ca/Sn alloys more compact, stable, and protective than AZ31 alloy. Therefore, AZ31 alloy bearing 0.2wt% Ca or Sn element exhibited excellent balanced properties, which is potential to be applied in commercial more comprehensively.
Research Article
Effects of Nd on microstructure and mechanical properties of as-cast Mg–12Gd–2Zn–xNd–0.4Zr alloys with stacking faults
Lixin Hong, Rongxiang Wang, and  Xiaobo Zhang
2022, vol. 29, no. 8, pp. 1570-1577. https://doi.org/10.1007/s12613-021-2264-8
Abstract:
In order to study the effects of Nd addition on microstructure and mechanical properties of Mg–Gd–Zn–Zr alloys, the microstructure and mechanical properties of the as-cast Mg–12Gd–2Zn–xNd–0.4Zr (x = 0, 0.5wt%, and 1wt%) alloys were investigated by using optical microscope, scanning electron microscope, X-ray diffractometer, nano indentation tester, microhardness tester, and tensile testing machine. The results show that the microstructures mainly consist of α-Mg matrix, eutectic phase, and stacking faults. The addition of Nd plays a significant role in grain refinement and uniform microstructure. The tensile yield strength and microhardness increase but the compression yield strength decreases with increasing Nd addition, leading to weakening tension–compression yield asymmetry in reverse of the Mg–12Gd–2Zn–xNd–0.4Zr alloys. The highest ultimate tensile strength (194 MPa) and ultimate compression strength (397 MPa) are obtained with 1wt% Nd addition of the alloy.
Research Article
Hot compressive deformation of eutectic Al–17at% Cu alloy on the interface of the Cu–Al composite plate produced by horizontal continuous casting
Jun Wang, Fan Zhao, Guoliang Xie, Jiaxuan Xu, and  Xinhua Liu
2022, vol. 29, no. 8, pp. 1578-1588. https://doi.org/10.1007/s12613-021-2276-4
Abstract:
On the interface of the Cu–Al composite plate from horizontal continuous casting, the eutectic microstructure layer thickness accounts for more than 90% of the total interface thickness, and the deformation in rolling forming plays an important role in the quality of the composite plate. The eutectic microstructure material on the interface of the Cu–Al composite plate was prepared by changing the cooling rate of ingot solidification and the deformation in hot compression was investigated. The results show that when the deformation temperature is over 300°C, the softening effect of dynamic recrystallization of α-Al is greater than the hardening effect, and uniform plastic deformation of eutectic microstructure is caused. The constitutive equation of flow stress in the eutectic microstructure layer was established by Arrhenius hyperbolic-sine mathematics model, providing a reliable theoretical basis for the deformation of the Cu–Al composite plate.
Research Article
Analysis of local microstructure and strengthening mechanisms in adjustable-gap bobbin tool friction stir welds of Al–Mg
Dong Wu, Wenya Li, Qiang Chu, Yangfan Zou, Xichang Liu, and  Yanjun Gao
2022, vol. 29, no. 8, pp. 1589-1595. https://doi.org/10.1007/s12613-021-2254-x
Abstract:
The bobbin tool friction stir welding process was used to join 6 mm thick 5A06 aluminum alloy plates. Optical microscope was used to characterize the microstructure. The electron backscatter diffraction (EBSD) identified the effect of non-homogeneous microstructure on the tensile properties. It was observed that the grain size in the top of the stir zone (SZ) is smaller than that in the centre region. The lowest ratio of recrystallization and density of the geometrically-necessary dislocations (GNDs) in the SZ was found in the middle near the thermo-mechanically affected zone (TMAZ) being 22% and 1.15 × 10−13 m−2, respectively. The texture strength of the heat-affected zone (HAZ) is the largest, followed by that in the SZ, with the lowest being in the TMAZ. There were additional interfaces developed which contributed to the strengthening mechanism, and their effect on tensile strength was analysed. The tensile tests identified the weakest part in the joint at the interfaces, and the specific reduction value is about 93 MPa.
Research Article
Evolution laws of microstructures and mechanical properties during heat treatments for near-α high-temperature titanium alloys
Xiaozhao Ma, Zhilei Xiang, Tao Li, Yilan Chen, Yingying Liu, Ziyong Chen, and  Qun Shu
2022, vol. 29, no. 8, pp. 1596-1607. https://doi.org/10.1007/s12613-021-2248-8
Abstract:
Evolution laws of microstructures, mechanical properties, and fractographs after different solution temperatures were investigated through various analysis methods. With the increasing solution temperatures, contents of the primary α phase decreased, and contents of transformed β structures increased. Lamellar α grains dominated the characteristics of transformed β structures, and widths of secondary α lamellas increased monotonously. For as-forged alloy, large silicides with equiaxed and rod-like morphologies, and nano-scale silicides were found. Silicides with large sizes might be (Ti, Zr, Nb)5Si3 and (Ti, Zr, Nb)6Si3. Rod-like silicides with small sizes precipitated in retained β phase, exhibiting near 45° angles with α/β boundaries. Retained β phases in as-heat treated alloys were incontinuous. 980STA exhibited an excellent combination of room temperature (RT) and 650°C mechanical properties. Characteristics of fracture surfaces largely depended on the evolutions of microstructures. Meanwhile, silicides promoted the formation of mico-voids.
Research Article
Intermetallic growth behavior during post deformation annealing in multilayer Ti/Al/Nb composite interfaces
R. Jafari and  B. Eghbali
2022, vol. 29, no. 8, pp. 1608-1617. https://doi.org/10.1007/s12613-021-2263-9
Abstract:
The tri-metal Ti–Al–Nb composites were processed through three procedures: hot pressing, rolling, and hot pressing, followed by subsequent rolling. The fabricated composites were then subjected to annealing at 600, 625, and 650°C temperatures at different times. Microstructure observation at the interfaces reveals that the increase in plastic deformation strain significantly affects TiAl3 intermetallic layers’ evolution and accelerates the layers’ growth. On the contrary, the amount of applied strain does not significantly affect the evolution of the NbAl3 intermetallic layer thickness. It was also found that Al and Ti atoms’ diffusion has occurred throughout the TiAl3 layer, but only Al atoms diffuse through the NbAl3 layer. The slow growth rate of the NbAl3 intermetallic layer is due to the lack of diffusion of Nb atoms and the high activation energy of Al atoms’ reaction with Nb atoms.
Research Article
Effect of particle micro-structure on the electrochemical properties of LiNi0.8Co0.1Mn0.1O2 cathode material
Zexun Tang, Hongqi Ye, Xin Ma, and  Kai Han
2022, vol. 29, no. 8, pp. 1618-1626. https://doi.org/10.1007/s12613-021-2296-0
Abstract:
Ni-rich layered material is a kind of high-capacity cathode to meet the requirement of electric vehicles. As for the typical LiNi0.8Co0.1Mn0.1O2 material, the particle formation is significant for electrochemical properties of the cathode. In this work, the structure, morphology, and electrochemical performance of LiNi0.8Co0.1Mn0.1O2 secondary particles and single crystals were systematically studied. A lower Ni2+/Ni3+ molar ratio of 0.66 and a lower residual alkali content of 0.228wt% were achieved on the surface of the single crystals. In addition, the single crystals showed a discharge capacity of 191.6 mAh/g at 0.2 C (~12 mAh/g lower than that of the secondary particles) and enhanced the electrochemical stability, especially when cycled at 50°C and in a wider electrochemical window (between 3.0 and 4.4 V vs. Li+/Li). The LiNi0.8Co0.1Mn0.1O2 secondary particles were suitable for applications requiring high specific capacity, whereas single crystals exhibited better stability, indicating that they are more suitable for use in long life requested devices.
Research Article
Novel confinement combustion method of nanosized WC/C for efficient electrocatalytic oxygen reduction
Pengqi Chen, Yunxiao Tai, Huan Wu, Yufei Gao, Jiayu Chen, and  Jigui Cheng
2022, vol. 29, no. 8, pp. 1627-1634. https://doi.org/10.1007/s12613-021-2265-7
Abstract:
Nanosized tungsten carbide (WC)/carbon (C) catalyst was synthesized via a novel ultra-rapid confinement combustion synthesis method. The amount of activated carbon (AC) plays an important role in the morphology and structure, controlling both the precursor and final powder. The WC particles synthesized inside the pores of the AC had been 10–20 nm because of the confinement of the pore structure and the large specific surface area of AC. When used for oxygen reduction performance, the half-wave potential was −0.24 V, and the electron transfer number was 3.45, indicating the main reaction process was the transfer of four electrons. The detailed electrocatalytic performance and underlying mechanism were investigated in this work. Our study provides a novel approach for the design of catalysts with new compositions and new structures, which are significant for promoting the commercialization of fuel cells.
Research Article
Preparation and characterization of ceramic materials with low thermal conductivity and high strength using high-calcium fly ash
Mana Rodchom, Panida Wimuktiwan, Kanit Soongprasit, Duangduen Atong, and  Supawan Vichaphund
2022, vol. 29, no. 8, pp. 1635-1645. https://doi.org/10.1007/s12613-021-2367-2
Abstract:
High calcium-fly ash (HCFA) collected from the Mae Moh electricity generating plant in Thailand was utilized as a raw material for ceramic production. The main compositions of HCFA characterized by X-ray fluorescence mainly consisted of 28.55wt% SiO2, 16.06wt% Al2O3, 23.40wt% CaO, and 17.03wt% Fe2O3. Due to high proportion of calcareous and ferruginous contents, HCFA was used for replacing the potash feldspar in amounts of 10wt%–40wt%. The influence of substituting high-calcium fly ash (0–40wt%) and sintering temperatures (1000–1200°C) on physical, mechanical, and thermal properties of ceramic-based materials was investigated. The results showed that the incorporation of HCFA in appropriate amounts could enhance the densification and the strength as well as reduce the thermal conductivity of ceramic samples. High proportion of calcareous and ferruginous constituents in fly ash promoted the vitrification behavior of ceramic samples. As a result, the densification was enhanced by liquid phase formation at optimum fly ash content and sintering temperature. In addition, these components also facilitated a more abundant mullite formation and consequently improved flexural strength of the ceramic samples. The optimum ceramic properties were achieved with adding fly ash content between 10wt%–30wt% sintered at 1150–1200°C. At 1200°C, the maximum flexural strength of ceramic-FA samples with adding fly ash 10wt%–30wt% (PSW-FA(10)–(30)) was obtained in the range of 92.25–94.71 MPa when the water absorption reached almost zero (0.03%). In terms of thermal insulation materials, the increase in fly ash addition had a positively effect on the thermal conductivity, due to the higher levels of porosity created by gas evolving from the inorganic decomposition reactions inside the ceramic-FA samples. The addition of 20wt%–40wt% high-calcium fly ash in ceramic samples sintered at 1150°C reduced the thermal conductivity to 14.78%–49.25%, while maintaining acceptable flexural strength values (~45.67–87.62 MPa). Based on these promising mechanical and thermal characteristics, it is feasible to utilize this high-calcium fly ash as an alternative raw material in clay compositions for manufacturing of ceramic tiles.