International Journal of Minerals, Metallurgy and Materials

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Kinetics of the electrochemical process of galena electrodes in the diethyldithiocarbamate solution

Li-li Cheng, Ti-chang Sun, Xian-ping Luo, Dian-zuo Wang

2010, 17(6): 669-674. doi: 10.1007/s12613-010-0372-y

中文摘要(303) PDF(139) SpringerLink

摘要:
The electrochemical process of galena in a pH 12.8 buffer solution was investigated using chronoamperometry and chronopotentiometry. To establish kinetic parameters on the surface of galena in the diethyldithiocarbamate solution, the exchange current density and the dependence of current density on reaction time were determined. Experimental results demonstrate that the exchange current density of galena is 1.585×10^-2 A/m² in the diethyldithiocarbamate-free solution. In the diethyldithiocarbamate solution, the thickness of lead diethyldithiocarbamate adsorbed on the surface of galena is 3.28 molecular layers, the diffusion coefficient of diethyldithiocarbamate on the surface of galena electrodes is 1.13×10^-10 m²/s, and the exchange current density of galena is 0.45 A/m². Lead diethyldithiocarbamate on the surface of galena is firmly adsorbed.

Magnetic and flotation studies of banded hematite quartzite (BHQ) ore for the production of pellet grade concentrate

B. Das, B. K. Mishra, S. Prakash, S. K. Das, P. S. R. Reddy, S. I. Angadi

2010, 17(6): 675-682. doi: 10.1007/s12613-010-0373-x

中文摘要(456) PDF(27) SpringerLink

摘要:
To identify and establish beneficiation techniques for banded hematite quartzite (BHQ) iron ore, a comprehensive research on BHQ ore treatment was carried out. The BHQ ore was assayed as 38.9wt% Fe, 42.5wt% SiO₂, and 1.0wt% Al₂O₃. In this ore, hematite and quartz are present as the major mineral phases where goethite, martite, and magnetite are present in small amounts. The liberation of hematite particles can be enhanced to about 82% by reducing the particle size to below 63 μm. The rejection of silica particles can be obtained by magnetic and flotation separation techniques. Overall, the BHQ ore can be enriched to 65.3wt% Fe at 61.9% iron recovery. A flowsheet has been suggested for the commercial exploitation of the BHQ ore.

Influence of fly ash fineness and shape on the porosity and permeability of blended cement pastes

Theerawat Sinsiri, Prinya Chindaprasirt, Chai Jaturapitakkul

2010, 17(6): 683-690. doi: 10.1007/s12613-010-0374-9

中文摘要(278) PDF(11) SpringerLink

摘要:
The effects of the fineness and shape of fly ash on the porosity and air permeability of cement pastes were investigated. Pulverized coal combustion (PCC) fly ash and fluidized bed coal combustion (FBC) fly ash classified into three different finenesses were used. River sand with particle size distribution similar to that of fly ash was also used for comparison. Portland cement was replaced with fly ash and ground sand at the dosages of 0, 20wt%, and 40wt%. A water-to-binder ratio (w/b) of 0.35 was used throughout the experiment. The results show that the porosity and air permeability of the pastes are influenced by the shape, fineness, and replacement level of fly ash. The porosity and air permeability of FBC fly ash pastes are higher than those of PCC fly ash pastes. This is due to the higher irregular shape and surface of FBC fly ash compared to the spherical shape and relatively smooth surface of PCC fly ash. The porosity increases with the increase in fly ash replacement level and decreases with the increase in its fineness. The permeability of PCC fly ash pastes decreases with the increase in replacement level and fineness, while for FBC fly ash, the permeability increases with the increase in replacement level. Decreases in porosity and permeability are due to a combined effect of the packing of fine particles and the reaction of fly ash.

Assessment of deterioration in RHA-concrete due to magnesium sulphate attack

G. A. Habeeb, H. B. Mahmud, N. B. A. A. Hamid

2010, 17(6): 691-696. doi: 10.1007/s12613-010-0375-8

中文摘要(253) PDF(13) SpringerLink

摘要:
The assessment of magnesium sulphate attack on concretes containing rice husk ash (RHA, 20wt% of the cementitious materials) with various average particle sizes was investigated. The total cementitious materials were 390 kg and the water-to-binder ratio (W/B) was 0.53 for all mixtures. Specimens were initially cured in water for 7 d and then immersed in the 3wt% magnesium sulphate solution for up to 111 d of exposure. The specimens were subjected to drying-wetting cycles to accelerate sulphate attack. In addition to the visual monitoring of the specimens, the concrete specimens were subsequently tested for compressive strength, dynamic modulus of elasticity, and length and mass changes. The results show that the specimens exposed to sulphate attack exhibit higher strength and dynamic modulus than those kept in water. The length change is negligible and can be attributed to the normal swelling of concrete. On the other hand, concretes suffers mass loss and surface spalling and softening; the fine RHA-concrete results in a better resistance. For the accelerated sulphate attack method used in this study, mass change and visual monitoring are recommended for assessing the deterioration degree and the effectiveness of supplementary cementitious materials to resist sulphate attack.

Surface turbulence in a physical model of a steel thin slab continuous caster

A. Hajari, M. Meratian

2010, 17(6): 697-703. doi: 10.1007/s12613-010-0376-7

中文摘要(248) PDF(8) SpringerLink

摘要:
In the thin slab continuous casting (TSCC) of steel, the issue of optimum fluid flow is very important due to higher casting speeds and has direct influence on the formation of solidified shells and the quality of final products. In the current work, a full-scale physical modeling of a thin slab caster on the basis of dimensionless Reynolds and Froude similarity criteria was constructed. The flow pattern in the funnel shaped mold with a new tetra-furcated submerged entry nozzle (SEN) was investigated. To determinate optimum operational parameters, some experiments were carried out under various casting conditions. The results show that the tetra-furcated design of the nozzle leads to a special flow pattern in the mold cavity with three-dimensional recirculating flow. It is also shown that the increase of casting speed and gas injection results in surface turbulence. On the other hand, using a higher depth of SEN decreases the vortex in the free surface of the caster. To avoid surface turbulent and related casting problems, it is recommended to use 30-cm and 40-cm SEN depth at the casting speeds of 3.5 and 4.5 m/min, respectively.

Physical modeling of gas-liquid interfacial fluctuation in a thick slab continuous casting mold with argon blowing

Shu-guo Zheng, Miao-yong Zhu

2010, 17(6): 704-708. doi: 10.1007/s12613-010-0377-6

中文摘要(227) PDF(10) SpringerLink

摘要:
Combining with the physical model of level fluctuation in a thick slab continuous casting mold with the cross-section of 1500 mm×280 mm and argon blowing, the rationalities of estimating the level fluctuation by three traditional quantitative approaches were discussed, and the effects of gas flowrate, casting speed, and the immersion depth of submerged entry nozzle (SEN) on the level fluctuation were also investigated. As a result, it seems that three traditional quantitative approaches are not very suitable for estimating the level fluctuation in a mold with argon blowing, so a new approach for estimating level fluctuation in the mold with argon blowing was presented. The experimental results show that the level fluctuation is mainly in the region around the nozzle wall. When the casting speeds are larger than a certain value, there is the escape of large bubbles near the nozzle wall, which causes an obvious increase of level fluctuation. Furthermore, optimal process parameters, viz., the gas flowrate of 6 NL/min, the casting speed of 1.1 m/min, and the immersion depth of 170 mm, are presented to restrain the level fluctuation by a physical model.

Optimization of mixing time in a ladle with dual plugs

Dian-qiao Geng, Hong Lei, Ji-cheng He

2010, 17(6): 709-714. doi: 10.1007/s12613-010-0378-5

中文摘要(292) PDF(12) SpringerLink

摘要:
Based on the two-phase fluid (Eulerian-Eulerian) model, a mathematical model about the gas-liquid flow and mixing behavior was developed to investigate the effect of the offset of dual plugs, the included angle of dual plugs with a center point, and gas flow rate on the mixing time in a ladle with dual plugs. Numerical results indicate that two types of recirculation zones exist in the ladle. One is the middle recirculation between gas and liquid plumes, and the other is the sidewall recirculation between plumes and the ladle sidewall. The correction shows that the mixing time is in proportion to -0.2676 power of gas flow rate. There is a unique optimum offset of dual plugs with a particular included angle, in turn, a unique optimum included angle of dual plugs exits with a particular offset.

A process model for BOF process based on bath mixing degree

Guang-hui Li, Bao Wang, Qing Liu, Xin-zhong Tian, Rong Zhu, Li-ning Hu, Guo-guang Cheng

2010, 17(6): 715-722. doi: 10.1007/s12613-010-0379-4

中文摘要(282) PDF(10) SpringerLink

摘要:
The process model for BOF process can be applied to predict the liquid steel composition and bath temperature during the whole steelmaking process. On the basis of the traditional three-stage decarburization theory, the concept of mixing degree was put forward, which was used to indicate the effect of oxygen jet on decarburization. Furthermore, a more practical process model for BOF steelmaking was developed by analyzing the effect of silicon, manganese, oxygen injection rate, oxygen lance height, and bath temperature on decarburization. Process verification and end-point verification for the process model have been carried out, and the verification results show that the prediction accuracy of carbon content reaches 82.6% (the range of carbon content at the end-point is less than 0.1wt%) and 85.7% (the range of carbon content at end-point is 0.1wt%–0.7wt%) when the absolute error is less than 0.02wt% and 0.05wt%, respectively.

Effects of the width and thickness of slabs on broadening in continuous casting

Jian-xun Fu, Jing-she Li, Hui Zhang

2010, 17(6): 723-728. doi: 10.1007/s12613-010-0380-y

中文摘要(194) PDF(12) SpringerLink

摘要:
A 3D viscoelastic-plastic thermal-mechanical coupled finite element model was built on the basis of the secondary development of the commercial software MSC.Marc. Numerical simulations were performed to study slab broadening in the secondary cooling zone. The effects of slab width and thickness on slab broadening were considered. The obtained results reveal that the width broadening is noticeable, and the ratio of ultimate broadening slightly increases with the increase of slab width. This agrees well with the measured data in practice. There is no obvious increase in ultimate broadening when the thickness of slabs increases.

Microstructural evolution and mechanical properties of aging high nitrogen austenitic stainless steels

Zhou-hua Jiang, Zu-rui Zhang, Hua-bing Li, Zhen Li, Ma Qi-feng

2010, 17(6): 729-736. doi: 10.1007/s12613-010-0381-x

中文摘要(295) PDF(10) SpringerLink

摘要:
The microstructural evolution of 18Cr18Mn2Mo0.77N high nitrogen austenitic stainless steel in aging treatment was investigated by optical microscopy (OM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The results show that hexagonal intergranular and cellular Cr₂N with a=0.478 nm and c=0.444 nm and body-centered cubic intermetallic χ phase with a=0.892 nm precipitate gradually in the isothermal aging treatment. The matrix nitrogen depletion due to the intergranular Cr₂N precipitation induces the decay of Vickers hardness, and the formation of cellular Cr₂N and χ phase causes the increase in the values. The impact toughness presents a monotonic decrease and SEM morphologies show the leading brittle intergranular fracture. The tensile strength and elongation deteriorate obviously except for the sample aged for 1 h in yield strength. Stress concentration occurs when the matrix dislocations pile up at the precipitation and matrix interfaces, and the interfacial dislocations may become precursors to the misfit dislocations, which can form small cleavage steps and accelerate the formation of cracks.

Grain refinement in the coarse-grained region of the heat-affected zone in low-carbon high-strength microalloyed steels

Ran Wei, Cheng-jia Shang, Kai-ming Wu

2010, 17(6): 737-741. doi: 10.1007/s12613-010-0382-9

中文摘要(337) PDF(14) SpringerLink

摘要:
The microstructural features and grain refinement in the coarse-grained region of the heat-affected zone in low-carbon high-strength microalloyed steels were investigated using optical microscopy, scanning electron microscopy, and electron backscattering diffraction. The coarse-grained region of the heat-affected zone consists of predominantly bainite and a small proportion of acicular ferrite. Bainite packets are separated by high angle boundaries. Acicular ferrite laths or plates in the coarse-grained region of the heat-affected zone formed prior to bainite packets partition austenite grains into many smaller and separate areas, resulting in fine-grained mixed microstructures. Electron backscattering diffraction analysis indicates that the average crystallographic grain size of the coarse-grained region of the heat-affected zone reaches 6–9 μm, much smaller than that of austenite grains.

Effect of Nb on the dynamic recrystallization behavior of high-grade pipeline steels

Tao Niu, Yong-lin Kang, Hong-wei Gu, Yu-qun Yin, Ming-liang Qiao, Jin-xing Jiang

2010, 17(6): 742-747. doi: 10.1007/s12613-010-0383-8

中文摘要(241) PDF(10) SpringerLink

摘要:
The dynamic recrystallization (DRX) behavior of high-grade X80/X100 pipeline steels with different Nb contents was investigated through single pass compression experiment using a Gleeble 1500 thermomechanical simulator. By the regression of stress-strain data obtained in the experiment, the deformation activation energy of DRX was identified, and the critical strain was calculated with the Poliak-Jonas (P-J) method. Based on the analysis, the occurrence condition and kinetics of DRX were determined. The results show that as the Nb content increases from 0.08wt% to 0.095wt%, the activation energy of recrystallization raises from 365 to 395 kJ/mol. The critical strain of DRX can be determined more accurately by the P-J method, and the ratios of critical strain to peak strain of X80 and X100 pipeline steels are 0.51 and 0.49, respectively, which are similar to the results achieved by other researchers and calculated with empirical formulae.

Incubation and development of corrosion in microstructures of low alloy steels under a thin liquid film of NaCl aqueous solution

Wen-hua Zhang, Shan-wu Yang, Jia Guo, Zhi-yong Liu, Xin-lai He

2010, 17(6): 748-755. doi: 10.1007/s12613-010-0384-7

中文摘要(243) PDF(8) SpringerLink

摘要:
Electrochemical measurement, optical microscopy, and scanning electron microscopy were employed to investigate the corrosion behavior of some low alloy steels. The steels were held under a thin liquid film of 0.5wt% NaCl aqueous solution. It is found that the steels with the same chemical composition but different microstructures exhibit obviously different corrosion behaviors. However, the corrosion behavior of the steels with different compositions but the same microstructures may be similar in the present investigation. The corrosion rate of bainite is slower than that of ferrite and pearlite. The corrosion products of bainite are uniform and fine. The size of carbon-rich phases produces a great impact on the corrosion of the steels, whether in the initial stage or in the long term. It is easy to induce large pitting for carbon-rich phases with large size, which damages the compactness of the rust layer.

Influence of Re-Ti modification on the high impact wear resistance of high Si bainitic cast steel

Jin-feng Huang, Hong-sheng Fang, Yan-kang Zheng

2010, 17(6): 756-762. doi: 10.1007/s12613-010-0385-6

中文摘要(244) PDF(9) SpringerLink

摘要:
The effect of rare earth (Re) and titanium (Ti) multi-modification on the impact wear behavior of Mn-B high-Si bainitic cast steel was investigated systematically. The experiments show that the impact wear resistance can be improved greatly with the addition of Re and Ti. Its wear loss is only about 1/3-1/2 as large as that of the unmodified bainitic cast steel. By the Re/Ti modification, coarse dendrite grains and bainitic/martensite duplex structure have been refined effectively, and the impact toughness of the bainitic cast steel is nearly tripled (10 mm×10 mm×55 mm, with unnotched sample). Consequently, the modified bainitic cast steel possesses good wear resistance under high impact. For both modified and unmodified bainitic cast steels, high hardness white layer and deformed zone are developed beneath the worn surface under the high impact wear, but the formation and propagation of cracks are different for these bainitic casting steels. Different models for the formation and propagation of cracks for both modified and unmodified bainitic cast steels under high impact wear are proposed.

FEM analysis of metal flowing behaviors in porthole die extrusion based on the mesh reconstruction technology of the welding process

Dong-nan Huang, Zhi-hao Zhang, Jing-yuan Li, Jian-xin Xie

2010, 17(6): 763-769. doi: 10.1007/s12613-010-0386-5

中文摘要(305) PDF(10) SpringerLink

摘要:
A reconstruction technology of finite element meshes based on reversal engineering was applied to solve mesh penetration and separation in the finite element simulation for the divergent extrusion. The 3D numerical simulation of the divergent extrusion process including the welding stage for complicated hollow sections was conducted. Based on the analysis of flowing behaviors, the flowing velocities of the alloy in portholes and near the welding planes were properly controlled through optimizing the expansion angle as well as porthole areas and positions. After the die structure optimization, defects such as warp, wrist, and the wavelike are eliminated, which improves the section-forming quality. Meanwhile, the temperature distribution in the cross section is uniform. Especially, the temperature of the C-shape notch with a larger thickness is lower than that of other regions in the cross section, which is beneficial for balancing the alloy flowing velocity.

A fractal-based model for the microstructure evolution of silicon bronze wires fabricated by dieless drawing

Zhen Wang, Xue-feng Liu, Yong He, Jian-xin Xie

2010, 17(6): 770-776. doi: 10.1007/s12613-010-0387-4

中文摘要(257) PDF(10) SpringerLink

摘要:
The back-propagation neural (BPN) network was proposed to model the relationship between the parameters of the dieless drawing process and the microstructures of the QSi3-1 silicon bronze alloy. Combined with image processing techniques, grain sizes and grain-boundary morphologies were respectively determined by the quantitative metallographic method and the fractal theory. The outcomes obtained show that the deformed microstructures exhibit typical fractal features, and the boundaries can be characterized quantitatively by fractal dimensions. With the temperature of 600–800℃ and the drawing speed of 0.67–1.00 mm·s^-1, either a lower temperature or a higher speed will cause a smaller grain size together with an elevated fractal dimension. The developed model can be capable for forecasting the microstructure evolution with a minimum error. The average relative errors between the predicted results and the experimental values of grain size and fractal dimension are 3.9% and 0.9%, respectively.

Study on NiO/Fe interface with X-ray photoelectron spectroscopy

Chun Feng, Jing-yan Zhang, Jiao Teng, Fu-ming Wang

2010, 17(6): 777-781. doi: 10.1007/s12613-010-0388-3

中文摘要(267) PDF(7) SpringerLink

摘要:
Different monolayers (ML) of Fe atoms were deposited on NiO (001) substrates or NiO underlayers using molecular beam epitaxy (MBE), pulse laser deposition (PLD), and magnetron sputtering (MS). The magnetic properties and microstructure of the films were studied. The apparent magnetic dead layer (MDL) is found to exist at the NiO/Fe interfaces of the MBE sample (about 2 ML MDL), the PLD sample (about 3 ML MDL), and the MS sample (about 4 ML MDL). X-ray photoelectron spectroscopy indicates the presence of ionic Fe (Fe²⁺ or Fe³⁺) and metallic Ni at the NiO/Fe interfaces, which may be due to the chemical reactions between Fe and NiO layers. This also leads to the formation of MDL. The thickness of the MDL and the reaction products are related with the deposition energy of the atoms on the substrates. The interfacial reactions are effectively suppressed by inserting a thin Pt layer at the NiO/Fe interface.

A new route of fabricating porous polyimide membranes

Jiu-mei Xiao, Xin-chun Shang, Li-ping Qin

2010, 17(6): 782-785. doi: 10.1007/s12613-010-0389-2

中文摘要(230) PDF(6) SpringerLink

摘要:
A novel experimental route to fabricate porous polyimide membranes (PPMs) with ideal air permeability was reported. The polymer solution layer consisting of the corresponding polyamic acid (PAA), solvent, and dibutyl phthalate (DBP) with a boiling temperature of 340℃ was treated by a simple process. The polymer solution layer was first treated at a lower temperature (about 150℃), then the received solid membrane was further imidized at a higher temperature (about 270℃), and finally, DBP was removed from the membrane at a temperature above its boiling temperature. The final asymmetric polyimide membrane with a dense skin layer was obtained. To improve the air permeability of the polyimide membranes, the polymer solution layer was treated between two substrates. And the PPMs with open pores on both sides are fabricated and the air permeability of the films is improved greatly.

Crystal structure and negative thermal expansion of solid solution Lu₂W_3-xMo_xO₁₂

Jie Peng, Xin-zhi Liu, Fu-li Guo, Song-bai Han, Yun-tao Liu, Dong-feng Chen, Zhong-bo Hu

2010, 17(6): 786-790. doi: 10.1007/s12613-010-0390-9

中文摘要(272) PDF(6) SpringerLink

摘要:
A new series of solid solutions Lu₂W_3-xMo_xO₁₂ (0.5≤x≤2.5) were successfully synthesized by the solid-state method. Their crystal structure and negative thermal expansion properties were studied using high-temperature X-ray powder diffraction and the Rietveld method. All samples of rare-earth tungstates and molybdates are found to crystallize in the same orthorhombic structure with space group Pnca and show the negative thermal expansion phenomena related to transverse vibration of bridging oxygen atoms in the structure. Thermal expansion coefficients (TEC) of Lu₂W_3-xMo_xO₁₂ are determined as -20.0×10^-6 K^-1 for x=0.5 and -16.1×10^-6 K^-1 for x=2.5 but -18.6×10^-6 and -16.9×10^-6 K^-1 for unsubstituted Lu₂W₃O₁₂ and Lu₂Mo₃O₁₂ in the identical temperature range of 200 to 800℃. High-temperature X-ray diffraction (XRD) data and bond length analysis suggest that the difference between W-O and Mo-O bond is responsible for the change of TECs after the element substitution in this series of solid solutions.

Cathodic behavior of molten CaCl₂-CaO and CaCl₂-NaCl-CaO

Shu-lan Wang, Wei Wang, Shi-chao Li, Shan-hui Cao

2010, 17(6): 791-794. doi: 10.1007/s12613-010-0391-8

中文摘要(260) PDF(9) SpringerLink

摘要:
The cathodic behavior of molten CaCl₂, CaCl₂-CaO and equimolar CaCl₂-NaCl-CaO was studied by cyclic voltammograms and constant potential polarization at temperatures of 1123 to 1173 K on molybdenum and titanium electrodes. The diffusion coefficient of Ca²⁺ (CaO) in molten CaCl₂-CaO was calculated from the linear relationship between the square root of scan rate and the peak current density. The deposition potentials and the potential temperature coefficient of CaO in molten CaCl₂-0.5mol%CaO and CaCl₂-NaCl-0.5mol%CaO were also obtained from their cyclic voltammograms. The result shows that CaO is more easily reduced than CaCl₂. The addition of NaCl in molten CaCl₂-CaO induces the underpotential electrodeposition of CaO.

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