Search2013 Vol. 20, No. 3
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2013, vol. 20, no. 3, pp.
221-227.
https://doi.org/10.1007/s12613-013-0716-5
Abstract:
Based on the fluidized roasting reduction technology of low-grade pyrolusite coupling with pretreatment of stone coal, the manganese reduction efficiency was investigated and technical conditions were optimized. It is found that the optimum manganese reduction efficiency can be up to 98.97% under the conditions that the mass ratio of stone coal to pyrolusite is 3:1, the roasting temperature of stone coal is 1000℃, the roasting temperature of pyrolusite is 800℃, and the roasting time is 2 h. Other low-grade pyrolusite ores in China from Guangxi, Hunan, and Guizhou Provinces were tested and all these minerals responded well, giving ~99% manganese reduction efficiency. Meanwhile, the reduction kinetic model has been established. It is confirmed that the reduction process is controlled by the interface chemical reaction. The apparent activation energy is 36.397 kJ/mol.
Based on the fluidized roasting reduction technology of low-grade pyrolusite coupling with pretreatment of stone coal, the manganese reduction efficiency was investigated and technical conditions were optimized. It is found that the optimum manganese reduction efficiency can be up to 98.97% under the conditions that the mass ratio of stone coal to pyrolusite is 3:1, the roasting temperature of stone coal is 1000℃, the roasting temperature of pyrolusite is 800℃, and the roasting time is 2 h. Other low-grade pyrolusite ores in China from Guangxi, Hunan, and Guizhou Provinces were tested and all these minerals responded well, giving ~99% manganese reduction efficiency. Meanwhile, the reduction kinetic model has been established. It is confirmed that the reduction process is controlled by the interface chemical reaction. The apparent activation energy is 36.397 kJ/mol.
2013, vol. 20, no. 3, pp.
228-233.
https://doi.org/10.1007/s12613-013-0717-4
Abstract:
The use of microwave energy in materials processing is a relatively new development presenting numerous advantages because of the rapid heating feature. Microwave technology has great potential to improve the extraction efficiency of metals in terms of both a reduction in required leaching time and an increase in the recovery of valuable metals. This method is especially pertinent in view of the increased demand for environment-friendly processes. In the present study, the influence of microwave heating on the direct leaching of chalcopyrite ores and concentrates were investigated. The results of microwave leaching experiments were compared with those obtained under conventional conditions. During these processes, parameters such as leaching media, temperature, and time have been worked to determine the optimum conditions for proper copper dissolution. Experimental results show that microwave leaching is more efficient than conventional leaching. The optimum leaching conditions for microwave leaching are the solid-to-liquid ratio of 1:100 g/mL, the temperature of 140℃, the solution of 0.5 M H2SO4 + 0.05 M Fe2(SO4)3, and the time of 1 h.
The use of microwave energy in materials processing is a relatively new development presenting numerous advantages because of the rapid heating feature. Microwave technology has great potential to improve the extraction efficiency of metals in terms of both a reduction in required leaching time and an increase in the recovery of valuable metals. This method is especially pertinent in view of the increased demand for environment-friendly processes. In the present study, the influence of microwave heating on the direct leaching of chalcopyrite ores and concentrates were investigated. The results of microwave leaching experiments were compared with those obtained under conventional conditions. During these processes, parameters such as leaching media, temperature, and time have been worked to determine the optimum conditions for proper copper dissolution. Experimental results show that microwave leaching is more efficient than conventional leaching. The optimum leaching conditions for microwave leaching are the solid-to-liquid ratio of 1:100 g/mL, the temperature of 140℃, the solution of 0.5 M H2SO4 + 0.05 M Fe2(SO4)3, and the time of 1 h.
2013, vol. 20, no. 3, pp.
234-245.
https://doi.org/10.1007/s12613-013-0718-3
Abstract:
An iron-silicate slag, from a zinc-copper smelting process, and mixtures of this slag with 5wt%, 10wt%, and 15wt% alumina addition were re-melted, semi-rapidly solidified, and characterized using scanning electron microscopy equipped with energy dispersive spectroscopy, and X-ray diffraction. The FactSageTM6.2 thermodynamic package was applied to compare the stable phases at equilibrium conditions with experimental characterization. A standard European leaching test was also carried out for all samples to investigate the changes in leaching behaviour because of the addition of alumina. Results show that the commonly reported phases for slags from copper and zinc production processes (olivine, pyroxene, and spinel) are the major constituents of the current samples. A correlation can be seen between mineralogical characteristics and leaching behaviours. The sample with 10wt% alumina addition, which contains high amounts of spinels and lower amounts of the other soluble phases, shows the lowest leachabilities for most of the elements.
An iron-silicate slag, from a zinc-copper smelting process, and mixtures of this slag with 5wt%, 10wt%, and 15wt% alumina addition were re-melted, semi-rapidly solidified, and characterized using scanning electron microscopy equipped with energy dispersive spectroscopy, and X-ray diffraction. The FactSageTM6.2 thermodynamic package was applied to compare the stable phases at equilibrium conditions with experimental characterization. A standard European leaching test was also carried out for all samples to investigate the changes in leaching behaviour because of the addition of alumina. Results show that the commonly reported phases for slags from copper and zinc production processes (olivine, pyroxene, and spinel) are the major constituents of the current samples. A correlation can be seen between mineralogical characteristics and leaching behaviours. The sample with 10wt% alumina addition, which contains high amounts of spinels and lower amounts of the other soluble phases, shows the lowest leachabilities for most of the elements.
2013, vol. 20, no. 3, pp.
246-252.
https://doi.org/10.1007/s12613-013-0719-2
Abstract:
An updated approach to refining the core indicators of pulverized coal used for blast furnace injection based on principal component analysis is proposed in view of the disadvantages of the existing performance indicator system of pulverized coal used in blast furnaces. This presented method takes into account all the performance indicators of pulverized coal injection, including calorific value, igniting point, combustibility, reactivity, flowability, grindability, etc. Four core indicators of pulverized coal injection are selected and studied by using principal component analysis, namely, comprehensive combustibility, comprehensive reactivity, comprehensive flowability, and comprehensive grindability. The newly established core index system is not only beneficial to narrowing down current evaluation indices but also effective to avoid previous overlapping problems among indicators by mutually independent index design. Furthermore, a comprehensive property indicator is introduced on the basis of the four core indicators, and the injection properties of pulverized coal can be overall evaluated.
An updated approach to refining the core indicators of pulverized coal used for blast furnace injection based on principal component analysis is proposed in view of the disadvantages of the existing performance indicator system of pulverized coal used in blast furnaces. This presented method takes into account all the performance indicators of pulverized coal injection, including calorific value, igniting point, combustibility, reactivity, flowability, grindability, etc. Four core indicators of pulverized coal injection are selected and studied by using principal component analysis, namely, comprehensive combustibility, comprehensive reactivity, comprehensive flowability, and comprehensive grindability. The newly established core index system is not only beneficial to narrowing down current evaluation indices but also effective to avoid previous overlapping problems among indicators by mutually independent index design. Furthermore, a comprehensive property indicator is introduced on the basis of the four core indicators, and the injection properties of pulverized coal can be overall evaluated.
2013, vol. 20, no. 3, pp.
253-258.
https://doi.org/10.1007/s12613-013-0720-9
Abstract:
Synthetic slag samples of the CaO-SiO2-MgO-Al2O3-Cr2O3 system were obtained to clarify the effect of FeO on the formation of spinel phases and Cr distribution. X-ray diffraction (XRD) and scanning electron microscopy (SEM) equipped with energy-dispersive spectroscopy (EDS), as well as the thermodynamic software FactSage 6.2, were used for sample characterization. The results show that the addition of FeO can decrease the viscosity of molten slag and the precipitation temperatures of melilite and merwinite. The solidus temperature significantly decreases from 1400 to 1250℃ with the increase of FeO content from 0wt% to 6wt%. The addition of FeO could enhance the content of Cr in spinel phases and reduce the content of Cr in soluble minerals, such as merwinite, melilite, and dicalcium silicate. Hence, the addition of FeO is conducive to decreasing Cr leaching.
Synthetic slag samples of the CaO-SiO2-MgO-Al2O3-Cr2O3 system were obtained to clarify the effect of FeO on the formation of spinel phases and Cr distribution. X-ray diffraction (XRD) and scanning electron microscopy (SEM) equipped with energy-dispersive spectroscopy (EDS), as well as the thermodynamic software FactSage 6.2, were used for sample characterization. The results show that the addition of FeO can decrease the viscosity of molten slag and the precipitation temperatures of melilite and merwinite. The solidus temperature significantly decreases from 1400 to 1250℃ with the increase of FeO content from 0wt% to 6wt%. The addition of FeO could enhance the content of Cr in spinel phases and reduce the content of Cr in soluble minerals, such as merwinite, melilite, and dicalcium silicate. Hence, the addition of FeO is conducive to decreasing Cr leaching.
2013, vol. 20, no. 3, pp.
259-265.
https://doi.org/10.1007/s12613-013-0721-8
Abstract:
Aging treatment and various heat input conditions were adopted to investigate the microstructural evolution and mechanical properties of TIG welded 6061-T6 alloy joints by microstructural observations, microhardness tests, and tensile tests. With an increase in heat input, the width of the heat-affected zone (HAZ) increases and grains in the fusion zone (FZ) coarsen. Moreover, the hardness of the HAZ decreases, whereas that of the FZ decreases initially and then increases with an increase in heat input. Low heat input results in the low ultimate tensile strength of the welded joints due to the presence of partial penetrations and pores in the welded joints. After a simple artificial aging treatment at 175℃ for 8 h, the microstructure of the welded joints changes slightly. The mechanical properties of the welded joints enhance significantly after the aging process as few precipitates distribute in the welded seam.
Aging treatment and various heat input conditions were adopted to investigate the microstructural evolution and mechanical properties of TIG welded 6061-T6 alloy joints by microstructural observations, microhardness tests, and tensile tests. With an increase in heat input, the width of the heat-affected zone (HAZ) increases and grains in the fusion zone (FZ) coarsen. Moreover, the hardness of the HAZ decreases, whereas that of the FZ decreases initially and then increases with an increase in heat input. Low heat input results in the low ultimate tensile strength of the welded joints due to the presence of partial penetrations and pores in the welded joints. After a simple artificial aging treatment at 175℃ for 8 h, the microstructure of the welded joints changes slightly. The mechanical properties of the welded joints enhance significantly after the aging process as few precipitates distribute in the welded seam.
2013, vol. 20, no. 3, pp.
266-272.
https://doi.org/10.1007/s12613-013-0722-7
Abstract:
The present work is focused on the microstructure and mechanical properties of Ti14 alloy with different semisolid deformation ratios during forging tests. The results revealed that the forging ratio had a significant effect on the precipitation of the alloy. Fewer plate-shaped Ti2Cu tended to precipitate on grain boundaries with higher forging ratios, and finally the plate-shaped Ti2Cu formed precipitate-free zones along grain boundaries with a forging ratio of 75%. The precipitation on grain boundaries was found to be controlled by a peritectic reaction. Large forging ratios accelerated the extrusion of liquid and resulted in less liquid along the prior grain boundaries, which reduced the peritectic precipitation in this region and formed precipitate-free zones during re-solidification. In addition, increasing the forging ratio could accelerate dynamic recrystallization, which is favorable for improving the semisolid formability. The tensile ductility increased with increasing forging ratio, and a mixed fracture mode, involving both cleavage and dimple fracture, was observed after forging with a forging ratio of 75%, which is attributed to the presence of precipitate-free zones formed along grain boundaries during semisolid processing.
The present work is focused on the microstructure and mechanical properties of Ti14 alloy with different semisolid deformation ratios during forging tests. The results revealed that the forging ratio had a significant effect on the precipitation of the alloy. Fewer plate-shaped Ti2Cu tended to precipitate on grain boundaries with higher forging ratios, and finally the plate-shaped Ti2Cu formed precipitate-free zones along grain boundaries with a forging ratio of 75%. The precipitation on grain boundaries was found to be controlled by a peritectic reaction. Large forging ratios accelerated the extrusion of liquid and resulted in less liquid along the prior grain boundaries, which reduced the peritectic precipitation in this region and formed precipitate-free zones during re-solidification. In addition, increasing the forging ratio could accelerate dynamic recrystallization, which is favorable for improving the semisolid formability. The tensile ductility increased with increasing forging ratio, and a mixed fracture mode, involving both cleavage and dimple fracture, was observed after forging with a forging ratio of 75%, which is attributed to the presence of precipitate-free zones formed along grain boundaries during semisolid processing.
2013, vol. 20, no. 3, pp.
273-278.
https://doi.org/10.1007/s12613-013-0723-6
Abstract:
Interdiffusion in the Fe2O3-TiO2 system was investigated by the diffusion couple method in the temperature range of 1323 to 1473 K. The diffusion concentration curves of Ti4+ cations were obtained by electron probe microanalysis, according to which the Boltzmann-Matano method optimized by Broeder was used to calculate the interdiffusion coefficients. The interdiffusion coefficients almost increased linearly with the mole fraction of Ti4+ cations increasing, and they were in the range of 10−12–10−11cm2·s−1. The increase of temperature could also lead to the increase of the interdiffusion coefficients at a constant concentration of Ti4+ cations. It was also found that the thickness growth of the diffusion layer obeyed the parabolic rate law.
Interdiffusion in the Fe2O3-TiO2 system was investigated by the diffusion couple method in the temperature range of 1323 to 1473 K. The diffusion concentration curves of Ti4+ cations were obtained by electron probe microanalysis, according to which the Boltzmann-Matano method optimized by Broeder was used to calculate the interdiffusion coefficients. The interdiffusion coefficients almost increased linearly with the mole fraction of Ti4+ cations increasing, and they were in the range of 10−12–10−11cm2·s−1. The increase of temperature could also lead to the increase of the interdiffusion coefficients at a constant concentration of Ti4+ cations. It was also found that the thickness growth of the diffusion layer obeyed the parabolic rate law.
2013, vol. 20, no. 3, pp.
279-283.
https://doi.org/10.1007/s12613-013-0724-5
Abstract:
(1 − x)PbZr0.54Ti0.46O3-xKNbO3 (0 ≤ x ≤ 25mol%) (abbreviated as PZT-xKN) piezoelectric ceramics were successfully fabricated by a traditional sintering technique at 1225℃ for 30 min. The influence of KNbO3 content on the crystal structure and electrical properties of the PZT-xKN piezoelectric ceramics was studied. Samples with 0 ≤ x ≤ 0.20 show a pure perovskite structure, indicating that all KNbO3 diffused into the crystal lattice of PZT to form a single solid solution in this compositional range. A second Pb3Nb4O13 phase is observed in the PZT-0.25KN sample, showing that the maximum solid solubility of KNbO3 in PZT matrix ceramic is less than 25mol%. Compared with pure PZT piezoelectric ceramics, samples containing KNbO3 have smaller crystal grains. PZT-0.15KN exhibits excellent piezoelectric properties with d33 = 209 pC/N.
(1 − x)PbZr0.54Ti0.46O3-xKNbO3 (0 ≤ x ≤ 25mol%) (abbreviated as PZT-xKN) piezoelectric ceramics were successfully fabricated by a traditional sintering technique at 1225℃ for 30 min. The influence of KNbO3 content on the crystal structure and electrical properties of the PZT-xKN piezoelectric ceramics was studied. Samples with 0 ≤ x ≤ 0.20 show a pure perovskite structure, indicating that all KNbO3 diffused into the crystal lattice of PZT to form a single solid solution in this compositional range. A second Pb3Nb4O13 phase is observed in the PZT-0.25KN sample, showing that the maximum solid solubility of KNbO3 in PZT matrix ceramic is less than 25mol%. Compared with pure PZT piezoelectric ceramics, samples containing KNbO3 have smaller crystal grains. PZT-0.15KN exhibits excellent piezoelectric properties with d33 = 209 pC/N.
2013, vol. 20, no. 3, pp.
284-289.
https://doi.org/10.1007/s12613-013-0725-4
Abstract:
TiC/Ti5Si3 composites were fabricated on Ti-5Al-2.5Sn substrates by gas tungsten arc welding (GTAW). Identification of the phases was performed using X-ray diffraction (XRD). The microstructures were analyzed using scanning electron microscopy (SEM) combined with energy-dispersive X-ray spectrometry (EDS) and optical microscopy (OM). The Vickers hardness was measured with a micro-hardness tester. The TiC/Ti5Si3 composites were obtained in a double-layer track, and the Vickers hardness of the track increased by two to three times compared with the Ti-5Al-2.5Sn substrate.
TiC/Ti5Si3 composites were fabricated on Ti-5Al-2.5Sn substrates by gas tungsten arc welding (GTAW). Identification of the phases was performed using X-ray diffraction (XRD). The microstructures were analyzed using scanning electron microscopy (SEM) combined with energy-dispersive X-ray spectrometry (EDS) and optical microscopy (OM). The Vickers hardness was measured with a micro-hardness tester. The TiC/Ti5Si3 composites were obtained in a double-layer track, and the Vickers hardness of the track increased by two to three times compared with the Ti-5Al-2.5Sn substrate.
2013, vol. 20, no. 3, pp.
290-297.
https://doi.org/10.1007/s12613-013-0726-3
Abstract:
β-Al3Mg2 intermetallic was used as a reinforcing agent to improve the mechanical properties of an aluminum matrix. Different amounts of Al3Mg2 nanoparticles (ranging from 0wt% to 20wt%) were milled with aluminum powders in a planetary ball mill for 10 h. Consolidation was conducted by uniaxial pressing at 400℃ under a pressure of 600 MPa for 2 h. Microstructural characterization confirms the uniform distribution of Al3Mg2 nanoparticles within the matrix. The effects of nano-sized Al3Mg2 content on the wear and mechanical properties of the composites were also investigated. The results show that as the Al3Mg2 content increases to higher levels, the hardness, compressive strength, and wear resistance of the nanocomposites increase significantly, whereas the relative density and ductility decrease. Scanning electron microscopy (SEM) analysis of worn surfaces reveals that a transition in wear mechanisms occurs from delamination to abrasive wear by the addition of Al3Mg2 nanoparticles to the matrix.
β-Al3Mg2 intermetallic was used as a reinforcing agent to improve the mechanical properties of an aluminum matrix. Different amounts of Al3Mg2 nanoparticles (ranging from 0wt% to 20wt%) were milled with aluminum powders in a planetary ball mill for 10 h. Consolidation was conducted by uniaxial pressing at 400℃ under a pressure of 600 MPa for 2 h. Microstructural characterization confirms the uniform distribution of Al3Mg2 nanoparticles within the matrix. The effects of nano-sized Al3Mg2 content on the wear and mechanical properties of the composites were also investigated. The results show that as the Al3Mg2 content increases to higher levels, the hardness, compressive strength, and wear resistance of the nanocomposites increase significantly, whereas the relative density and ductility decrease. Scanning electron microscopy (SEM) analysis of worn surfaces reveals that a transition in wear mechanisms occurs from delamination to abrasive wear by the addition of Al3Mg2 nanoparticles to the matrix.
2013, vol. 20, no. 3, pp.
298-306.
https://doi.org/10.1007/s12613-013-0727-2
Abstract:
Nano-sized MoSi2 powder was produced successfully from commercially available MoSi2 by a mechanical milling process carried out for 100 h, and mechanical alloying was employed to synthesize AA 2024-MoSi2 nanocomposites. The effects of MoSi2 reinforcement and mechanical milling on the structure, morphology, and iron contamination of the produced materials were investigated using X-ray diffraction, scanning electron microscopy, and atomic absorption spectrometry. It is revealed that the morphology of the aluminum alloy changes continuously during milling from spherical to plate-like, irregular, and finally equiaxed. The presence of MoSi2 reinforcement accelerates the milling process and results in a smaller average particle size. The Williamson-Hall method determined that the crystallite size of the aluminum alloy in the composite powder is smaller than that of the unreinforced alloy at the same milling time and this size reaches 45 nm after 16 h milling time. The Fe contamination content is higher for the nanocomposite in comparison with the unreinforced alloy because of the wearing role of MoSi2 hard particles.
Nano-sized MoSi2 powder was produced successfully from commercially available MoSi2 by a mechanical milling process carried out for 100 h, and mechanical alloying was employed to synthesize AA 2024-MoSi2 nanocomposites. The effects of MoSi2 reinforcement and mechanical milling on the structure, morphology, and iron contamination of the produced materials were investigated using X-ray diffraction, scanning electron microscopy, and atomic absorption spectrometry. It is revealed that the morphology of the aluminum alloy changes continuously during milling from spherical to plate-like, irregular, and finally equiaxed. The presence of MoSi2 reinforcement accelerates the milling process and results in a smaller average particle size. The Williamson-Hall method determined that the crystallite size of the aluminum alloy in the composite powder is smaller than that of the unreinforced alloy at the same milling time and this size reaches 45 nm after 16 h milling time. The Fe contamination content is higher for the nanocomposite in comparison with the unreinforced alloy because of the wearing role of MoSi2 hard particles.
2013, vol. 20, no. 3, pp.
307-312.
https://doi.org/10.1007/s12613-013-0728-1
Abstract:
A novel photodetector based on double-walled carbon nanotube (DWCNT) film/TiO2 nanotube array (TNA) heterojunctions was fabricated, which exhibited high photoresponse in a broad spectral range. The photoresponse of the detector was dramatically dependent on the length of the TNAs. High photocurrent-to-dark current ratio with a value of 3360 was observed in the visible range by optimizing the lengths of the TNAs. The photosensitive regions could be extended into the near-infrared range. These results reveal that DWCNT film/TNA heterojunctions show potential applications for broad band photodetectors.
A novel photodetector based on double-walled carbon nanotube (DWCNT) film/TiO2 nanotube array (TNA) heterojunctions was fabricated, which exhibited high photoresponse in a broad spectral range. The photoresponse of the detector was dramatically dependent on the length of the TNAs. High photocurrent-to-dark current ratio with a value of 3360 was observed in the visible range by optimizing the lengths of the TNAs. The photosensitive regions could be extended into the near-infrared range. These results reveal that DWCNT film/TNA heterojunctions show potential applications for broad band photodetectors.
2013, vol. 20, no. 3, pp.
313-322.
https://doi.org/10.1007/s12613-013-0729-0
Abstract:
Kaolin geopolymers were produced by the alkali-activation of kaolin with an activator solution (a mixture of NaOH and sodium silicate solutions). The NaOH solution was prepared at a concentration of 6–14 mol/L and was mixed with the sodium silicate solution at a Na2SiO3/NaOH mass ratio of 0.24 to prepare an activator solution. The kaolin-to-activator solution mass ratio used was 0.80. This paper aimed to analyze the effect of NaOH concentration on the compressive strength of kaolin geopolymers at 80℃ for 1, 2, and 3 d. Kaolin geopolymers were stable in water, and strength results showed that the kaolin binder had adequate compressive strength with 12 mol/L of NaOH concentration. When the NaOH concentration increased, the SiO2/Na2O decreased. The increased Na2O content enhanced the dissolution of kaolin as shown in X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) analyses. However, excess in this content was not beneficial for the strength development of kaolin geopolymers. In addition, there was the formation of more geopolymeric gel in 12 mol/L samples. The XRD pattern of the samples showed a higher amorphous content and a more geopolymer bonding existed as proved by FTIR analysis.
Kaolin geopolymers were produced by the alkali-activation of kaolin with an activator solution (a mixture of NaOH and sodium silicate solutions). The NaOH solution was prepared at a concentration of 6–14 mol/L and was mixed with the sodium silicate solution at a Na2SiO3/NaOH mass ratio of 0.24 to prepare an activator solution. The kaolin-to-activator solution mass ratio used was 0.80. This paper aimed to analyze the effect of NaOH concentration on the compressive strength of kaolin geopolymers at 80℃ for 1, 2, and 3 d. Kaolin geopolymers were stable in water, and strength results showed that the kaolin binder had adequate compressive strength with 12 mol/L of NaOH concentration. When the NaOH concentration increased, the SiO2/Na2O decreased. The increased Na2O content enhanced the dissolution of kaolin as shown in X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) analyses. However, excess in this content was not beneficial for the strength development of kaolin geopolymers. In addition, there was the formation of more geopolymeric gel in 12 mol/L samples. The XRD pattern of the samples showed a higher amorphous content and a more geopolymer bonding existed as proved by FTIR analysis.
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