Volume 39,Issue 5,2010 Table of Contents
2010, 39(5):753-755.
Abstract:
WO3 nanowires with various morphologies were prepared on nanoporous alumina template by a simple sol-gel method. X-ray diffraction analysis reveals that the obtained materials are cubic WO3. Scanning electron microscopy shows that the products contain chrysanthemum-shaped WO3 nanowires. The diameter of WO3 nanowires is about 10-80 nm and their length is up to several micrometers. Argon gas atmosphere is more favorable for WCl6-triblock copolymer sol to form WO3 nanowires with different morphologies on nanoporous alumina template than air atmosphere.
WO3 nanowires with various morphologies were prepared on nanoporous alumina template by a simple sol-gel method. X-ray diffraction analysis reveals that the obtained materials are cubic WO3. Scanning electron microscopy shows that the products contain chrysanthemum-shaped WO3 nanowires. The diameter of WO3 nanowires is about 10-80 nm and their length is up to several micrometers. Argon gas atmosphere is more favorable for WCl6-triblock copolymer sol to form WO3 nanowires with different morphologies on nanoporous alumina template than air atmosphere.
2010, 39(5):756-761.
Abstract:
Four instability criteria, namely Murty, Gegel, Malas and Prasad criteria, were compared, and the physical significance of parameters was analyzed in this paper. It is indicated that the instability map developed by Murty criterion is similar to Prasad criterion, showing an unstable flow at high strain rates. Murty criterion exhibits a little narrower unstable region. The instability maps developed by Malas criterion and Gegel criterion have similar shapes, and the unstable regions are wider than those Prasad criterion and Murty criterion. In addition to the unstable flow at high strain rates as predicted by Murty criterion and Prasad criterion, Malas criterion and Gegel criterion have a good ability for predicting unstable flow at high temperatures and low strain rates. The processing maps were validated by hot compression tests of Ti-22Al-25Nb alloy, and the possible causes of various instability were discussed.
Four instability criteria, namely Murty, Gegel, Malas and Prasad criteria, were compared, and the physical significance of parameters was analyzed in this paper. It is indicated that the instability map developed by Murty criterion is similar to Prasad criterion, showing an unstable flow at high strain rates. Murty criterion exhibits a little narrower unstable region. The instability maps developed by Malas criterion and Gegel criterion have similar shapes, and the unstable regions are wider than those Prasad criterion and Murty criterion. In addition to the unstable flow at high strain rates as predicted by Murty criterion and Prasad criterion, Malas criterion and Gegel criterion have a good ability for predicting unstable flow at high temperatures and low strain rates. The processing maps were validated by hot compression tests of Ti-22Al-25Nb alloy, and the possible causes of various instability were discussed.
2010, 39(5):762-766.
Abstract:
Single crystals of NiTi (with 50.0at% Ni) were prepared in a self-designed unidirectional solidification furnace with a graphite mold shell connected with a crystal selector. Both macrostructure and microstructure of the alloy were observed by OM and SEM with EDS, the grain orientation of single crystal was determined by XRD and pole figures, and shape memory effect was evaluated by an instrument developed by ourselves. The results show that dendritic features were presented in both cross section and longitudinal section; the direction of dendrites growth were close to solidified direction; there was no obvious grain boundary observed; the angle between normal direction of cross section and [111] orientation was 15°. Compared with normal NiTi polycrystals, the maximal recoverable strain and memory fatigue property of the alloy were improved because the bad effect of grain boundary on the martensite phase transformation was eliminated, and also [111] orientation was a preferred orientation of NiTi alloy which can provide larger recoverable strain.
Single crystals of NiTi (with 50.0at% Ni) were prepared in a self-designed unidirectional solidification furnace with a graphite mold shell connected with a crystal selector. Both macrostructure and microstructure of the alloy were observed by OM and SEM with EDS, the grain orientation of single crystal was determined by XRD and pole figures, and shape memory effect was evaluated by an instrument developed by ourselves. The results show that dendritic features were presented in both cross section and longitudinal section; the direction of dendrites growth were close to solidified direction; there was no obvious grain boundary observed; the angle between normal direction of cross section and [111] orientation was 15°. Compared with normal NiTi polycrystals, the maximal recoverable strain and memory fatigue property of the alloy were improved because the bad effect of grain boundary on the martensite phase transformation was eliminated, and also [111] orientation was a preferred orientation of NiTi alloy which can provide larger recoverable strain.
2010, 39(5):767-770.
Abstract:
Orthogonal design was applied to analyze the effect of simulation parameters on the thermal field and cooling curve during directional solidification using commercial finite-element analysis software ProCAST. The results show that solidification curves of single crystal superalloy vary greatly with several numerical simulation parameters and are particularly sensitive to the values of the heat transfer coefficient between the mold and test slab casting without core. The predictions of the temperature filed during solidification for slab geometries were compared with experimental results and calculated cooling curves are in good agreement with experimental measurements. The simulation parameters that had the greatest influence on high rate solidification (HRS) casting process simulation results were modified and determined.
Orthogonal design was applied to analyze the effect of simulation parameters on the thermal field and cooling curve during directional solidification using commercial finite-element analysis software ProCAST. The results show that solidification curves of single crystal superalloy vary greatly with several numerical simulation parameters and are particularly sensitive to the values of the heat transfer coefficient between the mold and test slab casting without core. The predictions of the temperature filed during solidification for slab geometries were compared with experimental results and calculated cooling curves are in good agreement with experimental measurements. The simulation parameters that had the greatest influence on high rate solidification (HRS) casting process simulation results were modified and determined.
2010, 39(5):771-774.
Abstract:
The tungsten-doped TiO2 powders were prepared by calcination process at different temperatures, with TiO2 as starting materials and WO3 as additive. The XRD and SEM were used to investigate the influence of calcination temperatures and the content of WO3 on the phase transformation of TiO2 powders. Moreover the transformation mechanism was discussed. The results show that the phase transformation from anatase to rutile of TiO2 powders is mainly attributed to the additive WO3. WO3 can promote the phase transformation and lower the transformation temperatures. The phase transformation of TiO2 are caused by two aspects of WO3, one is the replacement of some Ti4+ by Wn+ in TiO2 crystal lattice, and the other is the redox reaction between WO3 and TiO2. The replacement of Ti4+ by Wn+ during the redox reaction is believed to be the major factor influencing the phase transformation.
The tungsten-doped TiO2 powders were prepared by calcination process at different temperatures, with TiO2 as starting materials and WO3 as additive. The XRD and SEM were used to investigate the influence of calcination temperatures and the content of WO3 on the phase transformation of TiO2 powders. Moreover the transformation mechanism was discussed. The results show that the phase transformation from anatase to rutile of TiO2 powders is mainly attributed to the additive WO3. WO3 can promote the phase transformation and lower the transformation temperatures. The phase transformation of TiO2 are caused by two aspects of WO3, one is the replacement of some Ti4+ by Wn+ in TiO2 crystal lattice, and the other is the redox reaction between WO3 and TiO2. The replacement of Ti4+ by Wn+ during the redox reaction is believed to be the major factor influencing the phase transformation.
2010, 39(5):775-780.
Abstract:
Effects of sintering temperature, hot isostatic pressing（HIP）and heat-treatment on the microstructure, density and mechanical properties of Inconel718 alloy prepared by metal injection molding were investigated. The results show that the sintered alloy with a relative density of 98% can be achieved at 1275 °C. After HIP process, full density was achieved. After heat-treatment, a large amount of γ″ and γ′ phase were precipitated which increases the tensile strength and decreases the elongation of the alloy. The tensile strength and elongation were 1250 MPa and 21.7%, respectively, at room temperature, and 1177 MPa and 16.6% at 650 °C respectively, which are comparable with or superior to those of the wrought alloy.
Effects of sintering temperature, hot isostatic pressing（HIP）and heat-treatment on the microstructure, density and mechanical properties of Inconel718 alloy prepared by metal injection molding were investigated. The results show that the sintered alloy with a relative density of 98% can be achieved at 1275 °C. After HIP process, full density was achieved. After heat-treatment, a large amount of γ″ and γ′ phase were precipitated which increases the tensile strength and decreases the elongation of the alloy. The tensile strength and elongation were 1250 MPa and 21.7%, respectively, at room temperature, and 1177 MPa and 16.6% at 650 °C respectively, which are comparable with or superior to those of the wrought alloy.
2010, 39(5):781-786.
Abstract:
Air oxidation behavior of Ti60 alloy was studied in the temperature range from 600 oC to 750 oC. In addition to the determination of the oxidation kinetics by mass gain measurements, the morphology of the scales formed was observed by SEM and the phases present in the scales were characterized by X-ray diffraction. Results show that under the condition of oxidation at 600-750 oC for 0-100 h, the oxidation exponent n is between 1 and 2 calculated by oxidation experience formula of Wagner, the total oxidation energy is 256 kJ/mol, and the oxidation kinetics follows the linear-parabolic law. When Ti60 alloy was oxidized at 600 oC for 100 h or at 750 oC for 10 h, the oxidation product is TiO2, while there was a little Al2O3 on the surface when the alloy was oxidized at 750 oC for 100 h. The oxides were preferentially formed at the grain boundaries of the alloy. Besides the oxidation layer on the sample surface, oxygen also dissolves into the matrix to form brittle oxygen-enriched layer resulting in the mechanical property change. The oxygen-enriched layer was thickened with the increase of oxidation temperature and prolonging of the oxidation time.
Air oxidation behavior of Ti60 alloy was studied in the temperature range from 600 oC to 750 oC. In addition to the determination of the oxidation kinetics by mass gain measurements, the morphology of the scales formed was observed by SEM and the phases present in the scales were characterized by X-ray diffraction. Results show that under the condition of oxidation at 600-750 oC for 0-100 h, the oxidation exponent n is between 1 and 2 calculated by oxidation experience formula of Wagner, the total oxidation energy is 256 kJ/mol, and the oxidation kinetics follows the linear-parabolic law. When Ti60 alloy was oxidized at 600 oC for 100 h or at 750 oC for 10 h, the oxidation product is TiO2, while there was a little Al2O3 on the surface when the alloy was oxidized at 750 oC for 100 h. The oxides were preferentially formed at the grain boundaries of the alloy. Besides the oxidation layer on the sample surface, oxygen also dissolves into the matrix to form brittle oxygen-enriched layer resulting in the mechanical property change. The oxygen-enriched layer was thickened with the increase of oxidation temperature and prolonging of the oxidation time.
2010, 39(5):787-790.
Abstract:
Unidirectional heat flow is required during directional solidification, so it is very difficult to solidify directionally because of strong side radiation around a water-cold copper crucible. The feasibility of directional solidification with the cold crucible was analyzed by mathematic analysis from electromagnetism, temperature field and heat transfer. Results show that Joule heat is strongest at triple point, and it can counterweigh the side heat dissipation; therefore isotherms approach level near the contact point between the hump and the crucible. Increasing of the electromagnetic force and the degree of superheat of the melt can decrease side radiation of the crucible wall. Consequently it is possible to realize directional solidification with the cold crucible.
Unidirectional heat flow is required during directional solidification, so it is very difficult to solidify directionally because of strong side radiation around a water-cold copper crucible. The feasibility of directional solidification with the cold crucible was analyzed by mathematic analysis from electromagnetism, temperature field and heat transfer. Results show that Joule heat is strongest at triple point, and it can counterweigh the side heat dissipation; therefore isotherms approach level near the contact point between the hump and the crucible. Increasing of the electromagnetic force and the degree of superheat of the melt can decrease side radiation of the crucible wall. Consequently it is possible to realize directional solidification with the cold crucible.
2010, 39(5):791-795.
Abstract:
The influence of prior cold deformation after solution treatment on the α phase precipitation behavior during the subsequent aging treatment and final mechanical properties of TB3(Ti-10Mo-8V-1Fe-3.5Al) alloys was investigated. In the predeformed samples, network patterns were observed after aging treatment by metallographic microscope. Transmission electron microscopic (TEM) observation shows that in the predeformed-aged samples, the plate-shaped α precipitates prefer to nucleate and grow in high density dislocation sites, such as grain boundaries and slip bands. In addition, variant selection effects were observed in these samples. Results of X-ray diffraction and metallographic microscope indicate that α phase precipitation process could be accelerated in predeformed samples. Tensile test results reveal that by cold deformation the aging time could be shortened and the tensile strength could be enhanced, while the ductility could be reduced, in comparison with the freely aged sample.
The influence of prior cold deformation after solution treatment on the α phase precipitation behavior during the subsequent aging treatment and final mechanical properties of TB3(Ti-10Mo-8V-1Fe-3.5Al) alloys was investigated. In the predeformed samples, network patterns were observed after aging treatment by metallographic microscope. Transmission electron microscopic (TEM) observation shows that in the predeformed-aged samples, the plate-shaped α precipitates prefer to nucleate and grow in high density dislocation sites, such as grain boundaries and slip bands. In addition, variant selection effects were observed in these samples. Results of X-ray diffraction and metallographic microscope indicate that α phase precipitation process could be accelerated in predeformed samples. Tensile test results reveal that by cold deformation the aging time could be shortened and the tensile strength could be enhanced, while the ductility could be reduced, in comparison with the freely aged sample.
2010, 39(5):796-799.
Abstract:
An oxide layer was formed on the surface of Ti after micro-arc oxidation (MAO) treatment, which contained F-, Cl- and I-. Then the bacterial adhesion test was carried out. The results show that the titanium after surface modification by MAO has certain antibacterial activity to the common flora around the implant, whether they are aerobic or facultative anaerobic bacteria. At the same time, the F-, Cl- and I- ions in the oxide layer improve antibacterial properties further. Different crystalline structures result in different antibacterial properties. Under low voltage, the antibacterial properties of Ti are better due to the main product of anatase TiO2.
An oxide layer was formed on the surface of Ti after micro-arc oxidation (MAO) treatment, which contained F-, Cl- and I-. Then the bacterial adhesion test was carried out. The results show that the titanium after surface modification by MAO has certain antibacterial activity to the common flora around the implant, whether they are aerobic or facultative anaerobic bacteria. At the same time, the F-, Cl- and I- ions in the oxide layer improve antibacterial properties further. Different crystalline structures result in different antibacterial properties. Under low voltage, the antibacterial properties of Ti are better due to the main product of anatase TiO2.
2010, 39(5):800-803.
Abstract:
The quasi-static and dynamic compression mechanical performances of the U-Ti alloys aged at 200 oC for 4 h were tested by a mechanical equipment and Split Hopkinson Pressure Bar (SHPB) at room temperature. The adiabatic shearing characters of U-Ti alloys after dynamic compression were analyzed by SEM and OM. The results show that the U-Ti alloys are sensitive to strain rate because there is strengthening effect of strain rate. The 45o shear fracture had been yielded in the U-Ti alloys at the strain rate of 3600 s-1. Both the 45o shear fracture and ablative deformation were observed in U-Ti alloys when the strain rate reached 5000 s-1. Refusion phenomenon was found on the 45o fracture surface at the strain rate of 7300 s-1. The fracture morphology exhibits dimple character of plastic metal.
The quasi-static and dynamic compression mechanical performances of the U-Ti alloys aged at 200 oC for 4 h were tested by a mechanical equipment and Split Hopkinson Pressure Bar (SHPB) at room temperature. The adiabatic shearing characters of U-Ti alloys after dynamic compression were analyzed by SEM and OM. The results show that the U-Ti alloys are sensitive to strain rate because there is strengthening effect of strain rate. The 45o shear fracture had been yielded in the U-Ti alloys at the strain rate of 3600 s-1. Both the 45o shear fracture and ablative deformation were observed in U-Ti alloys when the strain rate reached 5000 s-1. Refusion phenomenon was found on the 45o fracture surface at the strain rate of 7300 s-1. The fracture morphology exhibits dimple character of plastic metal.
2010, 39(5):804-808.
Abstract:
High temperature compression simulation tests were carried out on Ti8LC alloy at a constant strain rate by a GLEEBLE-1500 thermal simulator, under the conditions of 850-1000 oC, 0.001-0.1 s-1 and maximal deformation of 60%. The effects of the strain rate and the forming temperature on the flow stress and the microstructure transition were investigated. The results reveal that the flow stress of Ti8LC increased as the strain rate increased, and at a constant strain rate the true stress decreased as the forming temperature increased. In the situation of experiment, the constitution equation of Ti8LC alloy was established by regression calculation. According to the experimental analysis, dynamic recrystallization happened while deformed at 850-950 oC. In addition the dynamic recovery was the mainly softening mechanism at evaluated temperature.
High temperature compression simulation tests were carried out on Ti8LC alloy at a constant strain rate by a GLEEBLE-1500 thermal simulator, under the conditions of 850-1000 oC, 0.001-0.1 s-1 and maximal deformation of 60%. The effects of the strain rate and the forming temperature on the flow stress and the microstructure transition were investigated. The results reveal that the flow stress of Ti8LC increased as the strain rate increased, and at a constant strain rate the true stress decreased as the forming temperature increased. In the situation of experiment, the constitution equation of Ti8LC alloy was established by regression calculation. According to the experimental analysis, dynamic recrystallization happened while deformed at 850-950 oC. In addition the dynamic recovery was the mainly softening mechanism at evaluated temperature.
2010, 39(5):809-813.
Abstract:
The oxide coatings were obtained on Ti6Al4V alloy in Na2SiO3 electrolyte system containing Li2SO4 by micro-arc oxidation (MAO). The thickness of coatings was measured and their surface micromorphology and roughness were analyzed by SEM and AFM, respectively. The results show that the thickness of coatings decreases from 87 μm to 57 μm and the roughness also decrease with the increasing of Li2SO4 content from 0 to 4.0 g/L in the electrolyte. Meantime, the diameter of cellular microholes on the surface of coatings decreases from 30 μm to 5 μm and the wall of microholes becomes smoother. The number of individual particles by melt spraying reduces from 416 to 145 but the average particle diameter increases from 350 nm to 597 nm. It is found by X-ray diffraction that the amount of rutile TiO2 in the coatings is increased and that of anatase TiO2 is reduced gradually with increasing of Li2SO4 content in the electrolyte.
The oxide coatings were obtained on Ti6Al4V alloy in Na2SiO3 electrolyte system containing Li2SO4 by micro-arc oxidation (MAO). The thickness of coatings was measured and their surface micromorphology and roughness were analyzed by SEM and AFM, respectively. The results show that the thickness of coatings decreases from 87 μm to 57 μm and the roughness also decrease with the increasing of Li2SO4 content from 0 to 4.0 g/L in the electrolyte. Meantime, the diameter of cellular microholes on the surface of coatings decreases from 30 μm to 5 μm and the wall of microholes becomes smoother. The number of individual particles by melt spraying reduces from 416 to 145 but the average particle diameter increases from 350 nm to 597 nm. It is found by X-ray diffraction that the amount of rutile TiO2 in the coatings is increased and that of anatase TiO2 is reduced gradually with increasing of Li2SO4 content in the electrolyte.
2010, 39(5):814-819.
Abstract:
A series of titania whiskers and Ti-Zr composite oxides were prepared by sol-gel method. Optimization of catalytic properties for meso-porous titania by doping zirconium was investigated. Effects of doping zirconium on crystal form, grain morphology, specific surface area and solid acidity of titania were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy disperse spectra (EDS), Fourier infrared spectroscopic analysis (FT-IR) with NH3 as atom probe and N2 physical adsorption (BET method). The results show that doping zirconium could prohibit crystal transformation from anatase to rutile, change the grain morphology, enhance the solid acidity and increase the specific surface area of titania. Consequently, the catalytic properties of titania were optimized. In the process of selective catalytic reduction of NO, with TiO2 as denitration catalyst and NH3 as reducing agent, doping zirconium widened the catalytic temperature range to high temperature by 50-100 ℃, and the biggest catalytic activity in the experimental temperature range was improved by 26.9%.
A series of titania whiskers and Ti-Zr composite oxides were prepared by sol-gel method. Optimization of catalytic properties for meso-porous titania by doping zirconium was investigated. Effects of doping zirconium on crystal form, grain morphology, specific surface area and solid acidity of titania were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy disperse spectra (EDS), Fourier infrared spectroscopic analysis (FT-IR) with NH3 as atom probe and N2 physical adsorption (BET method). The results show that doping zirconium could prohibit crystal transformation from anatase to rutile, change the grain morphology, enhance the solid acidity and increase the specific surface area of titania. Consequently, the catalytic properties of titania were optimized. In the process of selective catalytic reduction of NO, with TiO2 as denitration catalyst and NH3 as reducing agent, doping zirconium widened the catalytic temperature range to high temperature by 50-100 ℃, and the biggest catalytic activity in the experimental temperature range was improved by 26.9%.
2010, 39(5):820-823.
Abstract:
Sintering technique via microwave energy for WC-11.5Co cemented carbides and the effect of heating rate on the densification, microstructures and hardness (HRA) were investigated. Cemented carbides with high densification and hardness can be achieved by microwave sintering. Within the heating rate from 10.4 to 61.9 oC/min, it has no visible effect on alloys’ microstructures and properties. The harness ranging from 88.5 to 89.5 is obviously higher than 87.6 of conventionally sintered counterparts and the hardness index of YG11C commercial products.
Sintering technique via microwave energy for WC-11.5Co cemented carbides and the effect of heating rate on the densification, microstructures and hardness (HRA) were investigated. Cemented carbides with high densification and hardness can be achieved by microwave sintering. Within the heating rate from 10.4 to 61.9 oC/min, it has no visible effect on alloys’ microstructures and properties. The harness ranging from 88.5 to 89.5 is obviously higher than 87.6 of conventionally sintered counterparts and the hardness index of YG11C commercial products.
2010, 39(5):824-827.
Abstract:
The thermal barrier coating of La1.4Nd0.6Zr2O7(LNZ) on Mo substrate was prepared by the air plasma spraying with self-developed LNZ thermal spray powder. The thermal physical properties of LNZ powder were examined. The thermal shock resistence and thermal barrier effects of LNZ coatings were tested and compared with those of yttria stabilized zirconia(YSZ) thermal barrier coating. The results show that comparing with YSZ coating, LNZ thermal barrier coating is more suitable for Mo substrate because of its lower thermal expansion coefficient, lower thermal conductivity and sintering rate.
The thermal barrier coating of La1.4Nd0.6Zr2O7(LNZ) on Mo substrate was prepared by the air plasma spraying with self-developed LNZ thermal spray powder. The thermal physical properties of LNZ powder were examined. The thermal shock resistence and thermal barrier effects of LNZ coatings were tested and compared with those of yttria stabilized zirconia(YSZ) thermal barrier coating. The results show that comparing with YSZ coating, LNZ thermal barrier coating is more suitable for Mo substrate because of its lower thermal expansion coefficient, lower thermal conductivity and sintering rate.
2010, 39(5):828-831.
Abstract:
The processes of crack propagation in the La2O3-dispersed-strengthened molybdenum alloy were studied by in situ observation of transmission electron microscope. The results show that the paths of crack propagation in the alloy are dependent on the grain size of the molybdenum matrix and the shape and size of La2O3 particles. The crack propagates along the grain boundary of the matrix when it meets very fine molybdenum particles; the crack directly passes through the La2O3 particles to propagate when it meets micron-sized coarse rod-shaped La2O3 particles; the crack detours the particles and deflects when it meets sub-micron-sized ellipsoid-shaped La2O3 particles; the crack is pinned and then goes on propagating in zigzag or by bridging when it meets the nanosized fine and spherical La2O3 particles. Based on these experimental results, the mechanism of fine-grain toughening and particle-toughening of La2O3-dispersed- strengthened molybdenum were discussed from the aspect of the crack propagation paths and energy dissipation.
The processes of crack propagation in the La2O3-dispersed-strengthened molybdenum alloy were studied by in situ observation of transmission electron microscope. The results show that the paths of crack propagation in the alloy are dependent on the grain size of the molybdenum matrix and the shape and size of La2O3 particles. The crack propagates along the grain boundary of the matrix when it meets very fine molybdenum particles; the crack directly passes through the La2O3 particles to propagate when it meets micron-sized coarse rod-shaped La2O3 particles; the crack detours the particles and deflects when it meets sub-micron-sized ellipsoid-shaped La2O3 particles; the crack is pinned and then goes on propagating in zigzag or by bridging when it meets the nanosized fine and spherical La2O3 particles. Based on these experimental results, the mechanism of fine-grain toughening and particle-toughening of La2O3-dispersed- strengthened molybdenum were discussed from the aspect of the crack propagation paths and energy dissipation.
2010, 39(5):832-837.
Abstract:
First-principle calculation was carried out on the Ti of hcp structure and Ti-H system supercells by a total-energy plane-wave ultrasoft pseudopotential method based on density functional theory (DFT), which combined generalized gradient approximation(GGA). Lattice parameters, total energy, energy band structure, density of states (DOS) and Mulliken population of the system were obtained. The calculated results reveal that after H atom introduction into the crystal cell of Ti8, Ti16 and Ti32, the formation energy of crystal impurity was decreased and the volume of crystal cell was swollen; the distortion would become serious and the volume would be increased obviously along with increase of the hydrogen concentration in the crystal cell. The intensity of the great mass of Ti-Ti bonds were enhanced in the octahedron storing H atom of crystal cell. The Femi energy level moved to the direction of low energy of DOS. The activity of Ti alloys was improved, and the transferred electrons were mainly those on the P orbit of Ti.
First-principle calculation was carried out on the Ti of hcp structure and Ti-H system supercells by a total-energy plane-wave ultrasoft pseudopotential method based on density functional theory (DFT), which combined generalized gradient approximation(GGA). Lattice parameters, total energy, energy band structure, density of states (DOS) and Mulliken population of the system were obtained. The calculated results reveal that after H atom introduction into the crystal cell of Ti8, Ti16 and Ti32, the formation energy of crystal impurity was decreased and the volume of crystal cell was swollen; the distortion would become serious and the volume would be increased obviously along with increase of the hydrogen concentration in the crystal cell. The intensity of the great mass of Ti-Ti bonds were enhanced in the octahedron storing H atom of crystal cell. The Femi energy level moved to the direction of low energy of DOS. The activity of Ti alloys was improved, and the transferred electrons were mainly those on the P orbit of Ti.
2010, 39(5):838-842.
Abstract:
A series of Ti-B complexes with different composition and Mg45Ti3V2Ni50 hydrogen-storage alloys were synthesized by ball-milling. The effect of modification of Ti-B complexes on the cycle stability of Mg45Ti3V2Ni50 alloys was discussed and the Ti3B4 with a better comprehensive modification effect for Mg45Ti3V2Ni50 alloy electrode was selected. Mg45Ti3V2Ni50 -alloy electrode was modified with different mass ratios of Ti3B4 by ball-milling. The results show that the improvement degree of cycle stability and persistence is different due to different ratios of modification. There is a best composition of Ti-B and ratio of modification in the surface-modification process of Ti-B for the Mg-based hydrogen storage alloys in order to improve the cycle stability
A series of Ti-B complexes with different composition and Mg45Ti3V2Ni50 hydrogen-storage alloys were synthesized by ball-milling. The effect of modification of Ti-B complexes on the cycle stability of Mg45Ti3V2Ni50 alloys was discussed and the Ti3B4 with a better comprehensive modification effect for Mg45Ti3V2Ni50 alloy electrode was selected. Mg45Ti3V2Ni50 -alloy electrode was modified with different mass ratios of Ti3B4 by ball-milling. The results show that the improvement degree of cycle stability and persistence is different due to different ratios of modification. There is a best composition of Ti-B and ratio of modification in the surface-modification process of Ti-B for the Mg-based hydrogen storage alloys in order to improve the cycle stability
Zhao Yuanhua
,
Chen Yungui
,
Tang Yongbai
,
Xiao Sufen
,
Wei Shanghai
,
Zhang Xiaoping
,
Wang Qing
,
Tu Mingjing
2010, 39(5):843-847.
Abstract:
The microstructures and phase composition of as-cast AZ91+xLa alloys (x=0%, 0.3%, 0.5%, 0.7%, 1.0%, 1.5% and 2.0%, mass fraction) were investigated by SEM and XRD, and their mechanical properties were tested at room temperature. When 0.3%-2.0% La was added into the AZ91 alloys, Al11La3 phase was precipitated along the grain boundaries and interdendritic boundaries, and its morphology changed from acicular to flake gradually as the La content was increased. Meanwhile the size and volume fraction of β-Mg17Al12 phase was decreased. Moreover, the grain sizes of α-Mg were greatly reduced with La addition, and the best refinement is obtained in alloys containing 1.0%-1.5% La. Mechanical properties of AZ91 magnesium alloy can be improved significantly by addition of La, which results from the fine-grain strengthening of La, the optimization of the morphology and amount of β-Mg17Al12 phase and dispersion strengthening etc. Among all the investigated alloys, the AZ91+1.5%La alloy exhibits the optimum mechanical properties, i.e. the ultimate tensile strength is 226 MPa and the elongation 7.5% at room temperature.
The microstructures and phase composition of as-cast AZ91+xLa alloys (x=0%, 0.3%, 0.5%, 0.7%, 1.0%, 1.5% and 2.0%, mass fraction) were investigated by SEM and XRD, and their mechanical properties were tested at room temperature. When 0.3%-2.0% La was added into the AZ91 alloys, Al11La3 phase was precipitated along the grain boundaries and interdendritic boundaries, and its morphology changed from acicular to flake gradually as the La content was increased. Meanwhile the size and volume fraction of β-Mg17Al12 phase was decreased. Moreover, the grain sizes of α-Mg were greatly reduced with La addition, and the best refinement is obtained in alloys containing 1.0%-1.5% La. Mechanical properties of AZ91 magnesium alloy can be improved significantly by addition of La, which results from the fine-grain strengthening of La, the optimization of the morphology and amount of β-Mg17Al12 phase and dispersion strengthening etc. Among all the investigated alloys, the AZ91+1.5%La alloy exhibits the optimum mechanical properties, i.e. the ultimate tensile strength is 226 MPa and the elongation 7.5% at room temperature.
2010, 39(5):848-852.
Abstract:
In order to realize numerical simulation of plastic forming and to establish the reasonable hot formation process, the high-temperature compressive deformation behavior of AZ80 alloy was studied at various deformation temperatures and strain rates with Gleeble-1500. The experimental results show that the softening mechanism of dynamic recovery and dynamic recrystallization is a feature of high-temperature flow stress-strain curves of AZ80 alloy, and the peak stress increases with decreasing of the deformation temperature or increasing of the strain rate. Based on the true stress-strain curves, the established constitutive equation represents high temperature flow behavior of AZ80 alloy, and the calculated results of the flow stress are in good agreement with the experimental results of high temperature deformation of AZ80 alloy. Meanwhile, the obtained processing map of Dynamic Material Modeling (DMM) is used to analyze the deformation mechanism and the destabilization mechanism of AZ80 alloy; the optimal deformation processing parameters are the deformation temperatures ranging from 300 to 350 oC and strain rates ranging from 0.001 to 0.01 s-1, when the mechanical property of AZ80 alloy is taken into consideration.
In order to realize numerical simulation of plastic forming and to establish the reasonable hot formation process, the high-temperature compressive deformation behavior of AZ80 alloy was studied at various deformation temperatures and strain rates with Gleeble-1500. The experimental results show that the softening mechanism of dynamic recovery and dynamic recrystallization is a feature of high-temperature flow stress-strain curves of AZ80 alloy, and the peak stress increases with decreasing of the deformation temperature or increasing of the strain rate. Based on the true stress-strain curves, the established constitutive equation represents high temperature flow behavior of AZ80 alloy, and the calculated results of the flow stress are in good agreement with the experimental results of high temperature deformation of AZ80 alloy. Meanwhile, the obtained processing map of Dynamic Material Modeling (DMM) is used to analyze the deformation mechanism and the destabilization mechanism of AZ80 alloy; the optimal deformation processing parameters are the deformation temperatures ranging from 300 to 350 oC and strain rates ranging from 0.001 to 0.01 s-1, when the mechanical property of AZ80 alloy is taken into consideration.
2010, 39(5):853-856.
Abstract:
Non-equilibrium molecular dynamics (NEMD) method was used to simulate the thermal conductivity of monocrystal germanium thin films on the out-of plane. In the simulation, the thickness of the films ranged from 2.8288 to 11.315 nm and the average temperature was 400 K. The results of calculations demonstrate that the thermal conductivity of the monocrystal germanium thin film increases nearly linearly with increasing of the film thickness, which is remarkably lower than the corresponding experimental data of bulk germanium. For a given film thickness, the thermal conductivity of the nanometer thin film varies slightly with increasing of the temperature, and its size effect is significant comparing with the thermal conductivity of bulks.
Non-equilibrium molecular dynamics (NEMD) method was used to simulate the thermal conductivity of monocrystal germanium thin films on the out-of plane. In the simulation, the thickness of the films ranged from 2.8288 to 11.315 nm and the average temperature was 400 K. The results of calculations demonstrate that the thermal conductivity of the monocrystal germanium thin film increases nearly linearly with increasing of the film thickness, which is remarkably lower than the corresponding experimental data of bulk germanium. For a given film thickness, the thermal conductivity of the nanometer thin film varies slightly with increasing of the temperature, and its size effect is significant comparing with the thermal conductivity of bulks.
2010, 39(5):857-861.
Abstract:
In order to provide theoretical guidance for hot working and heat treatment, the equilibrium precipitated phases and the effect of elements on the thermodynamic equilibrium phases for GH720Li superalloy were studied by Thermo-Calc software. The calculated results show that there is serious segregation of Mo and Ti during the solidification of the superalloy. The quantitative rule of the contents of Al and Ti on the precipitation temperature and mass fraction of γ' phase is presented. Increment of C content leads to more precipitation of carbides, but it has no effect on their precipitation temperatures. Cr can not change the precipitation content of M23C6, but it can increase the precipitation temperature remarkably. Furthermore, the relation between the precipitated temperature of MC and initial melting point of GH720Li superalloy was studied.
In order to provide theoretical guidance for hot working and heat treatment, the equilibrium precipitated phases and the effect of elements on the thermodynamic equilibrium phases for GH720Li superalloy were studied by Thermo-Calc software. The calculated results show that there is serious segregation of Mo and Ti during the solidification of the superalloy. The quantitative rule of the contents of Al and Ti on the precipitation temperature and mass fraction of γ' phase is presented. Increment of C content leads to more precipitation of carbides, but it has no effect on their precipitation temperatures. Cr can not change the precipitation content of M23C6, but it can increase the precipitation temperature remarkably. Furthermore, the relation between the precipitated temperature of MC and initial melting point of GH720Li superalloy was studied.
2010, 39(5):862-866.
Abstract:
A series of Dy(Gd)-based bulk metallic glasses with small atoms of B and N were prepared by casting the melt ingots into a water-cooled copper mould. Their phase structure was analyzed by X-ray diffraction. The glass transition and crystallization behavior were measured by differential scanning calorimetry (DSC). Kinetics parameters of crystallization such as crystallization activation energy, frequency factor and crystallization rate constant were calculated by Kissinger equation and Arrehenius law. The results show that for the Dy31Gd25Co20Al24 alloy with addition of small atoms of B and N, the crystallization model changed; both the supercooled liquid region and crystallization activation energy were first decreased and then increased; with added B atom, crystallization rate constant of the alloy was first increased and then decreased; while with added N atom, crystallization rate constant was first decreased and then increased.
A series of Dy(Gd)-based bulk metallic glasses with small atoms of B and N were prepared by casting the melt ingots into a water-cooled copper mould. Their phase structure was analyzed by X-ray diffraction. The glass transition and crystallization behavior were measured by differential scanning calorimetry (DSC). Kinetics parameters of crystallization such as crystallization activation energy, frequency factor and crystallization rate constant were calculated by Kissinger equation and Arrehenius law. The results show that for the Dy31Gd25Co20Al24 alloy with addition of small atoms of B and N, the crystallization model changed; both the supercooled liquid region and crystallization activation energy were first decreased and then increased; with added B atom, crystallization rate constant of the alloy was first increased and then decreased; while with added N atom, crystallization rate constant was first decreased and then increased.
2010, 39(5):867-870.
Abstract:
Vanadium oxide thin films were fabricated on muscovite (001) substrates by sol-gel method, and the polycrystalline VO2 films were obtained by subsequent high temperature annealing. The morphology, optic properties and thermochromic phase transition characteristics of vanadium dioxide thin films annealed at different heating rate were investigated by SEM and FTIR. Results show that after annealed at the heating rate of 8 oC/min, the VO2 films exhibit excellent thermochromic phase transition characteristics with phase transition temperature of 65 oC and hysteresis width of 10 oC.
Vanadium oxide thin films were fabricated on muscovite (001) substrates by sol-gel method, and the polycrystalline VO2 films were obtained by subsequent high temperature annealing. The morphology, optic properties and thermochromic phase transition characteristics of vanadium dioxide thin films annealed at different heating rate were investigated by SEM and FTIR. Results show that after annealed at the heating rate of 8 oC/min, the VO2 films exhibit excellent thermochromic phase transition characteristics with phase transition temperature of 65 oC and hysteresis width of 10 oC.
2010, 39(5):871-873.
Abstract:
A new type of amorphous Fe96Nb4 core soft-magnetic thin film suitable for silicon-based micro-fluxgate was prepared by magnetron sputtering technique. Its phase composition, surface morphology and magnetic hysteresis loop were characterized by X-ray diffractometer, SEM and VSM (vibration sample magnetometer), respectively. The core film was examined by a double-cores fluxgate sensor. The results show that the defects of films decrease when they are prepared at high temperature. Meanwhile, its soft magnetic properties are improved significantly. Silicon-based Fe96Nb4 core thin film prepared at 630 K of the substrate is suitable for the application in the micro-fluxgate iron core materials.
A new type of amorphous Fe96Nb4 core soft-magnetic thin film suitable for silicon-based micro-fluxgate was prepared by magnetron sputtering technique. Its phase composition, surface morphology and magnetic hysteresis loop were characterized by X-ray diffractometer, SEM and VSM (vibration sample magnetometer), respectively. The core film was examined by a double-cores fluxgate sensor. The results show that the defects of films decrease when they are prepared at high temperature. Meanwhile, its soft magnetic properties are improved significantly. Silicon-based Fe96Nb4 core thin film prepared at 630 K of the substrate is suitable for the application in the micro-fluxgate iron core materials.
2010, 39(5):874-877.
Abstract:
The Pd/γ-Al2O3 catalyst was prepared by a dipping method. The catalyst was characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and temperature programmed reduction (TPR). The catalytic properties of the Pd/γ-Al2O3 catalyst for the hydrogen-deuterium exchange of methane were tested with a fixed-bed micro-reactor. The results indicate that the Pd atoms are in the support interior of the Pd/γ-Al2O3 catalyst and the strong interaction between Pd and the support on the Pd/γ-Al2O3 catalyst occurs. The Pd/γ-Al2O3 catalyst possesses high catalytic activity in the hydrogen-deuterium exchange of methane.
The Pd/γ-Al2O3 catalyst was prepared by a dipping method. The catalyst was characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and temperature programmed reduction (TPR). The catalytic properties of the Pd/γ-Al2O3 catalyst for the hydrogen-deuterium exchange of methane were tested with a fixed-bed micro-reactor. The results indicate that the Pd atoms are in the support interior of the Pd/γ-Al2O3 catalyst and the strong interaction between Pd and the support on the Pd/γ-Al2O3 catalyst occurs. The Pd/γ-Al2O3 catalyst possesses high catalytic activity in the hydrogen-deuterium exchange of methane.
2010, 39(5):883-888.
Abstract:
The effect of the backpressure on the plastic deformation of the billet material was investigated by finite element simulation in the equal channel angular pressing/extrusion (ECAP) process. The multiple-pass ECAP experiment results were also analyzed. The results show that the degree and uniformity of plastic deformation can be effectively enhanced by backpressure application during ECAP for every pass. In the multiple-pass ECAP experiment, there is a decrease in the equilibrium grain size and the processing temperature in the ECAP process with backpressure.
The effect of the backpressure on the plastic deformation of the billet material was investigated by finite element simulation in the equal channel angular pressing/extrusion (ECAP) process. The multiple-pass ECAP experiment results were also analyzed. The results show that the degree and uniformity of plastic deformation can be effectively enhanced by backpressure application during ECAP for every pass. In the multiple-pass ECAP experiment, there is a decrease in the equilibrium grain size and the processing temperature in the ECAP process with backpressure.
2010, 39(5):889-891.
Abstract:
Ar+ ion beam was used to sputter the uranium film surface. Through measurement and analysis of white light interferometer and step device, the influence of sputter energy and incidence angle of the Ar+ ion beam on the surface roughness Ra of uranium film was researched, and that was compared with the etching test of Ar+ ion beam. Results show that with the incidence angle of 30o and increasing of the sputter time, the uranium film sputtered by Ar+ ion beam of 0.5 keV energy has smaller roughness and smoother surface than that sputtered by the beam of 1.0 keV energy. The sputter depth of the beam with 0.5 keV is only a few nanometers but the etching effect on Mo film is opposite. Ar+ ion beam sputter has the fine polishing effect on material surface. With the assistance of ion beam micron-sized etching thinning, it can be used for precision machining of uranium film surface.
Ar+ ion beam was used to sputter the uranium film surface. Through measurement and analysis of white light interferometer and step device, the influence of sputter energy and incidence angle of the Ar+ ion beam on the surface roughness Ra of uranium film was researched, and that was compared with the etching test of Ar+ ion beam. Results show that with the incidence angle of 30o and increasing of the sputter time, the uranium film sputtered by Ar+ ion beam of 0.5 keV energy has smaller roughness and smoother surface than that sputtered by the beam of 1.0 keV energy. The sputter depth of the beam with 0.5 keV is only a few nanometers but the etching effect on Mo film is opposite. Ar+ ion beam sputter has the fine polishing effect on material surface. With the assistance of ion beam micron-sized etching thinning, it can be used for precision machining of uranium film surface.
2010, 39(5):892-895.
Abstract:
Tungsten copper composite for sputtering materials was fabricated by sintering a tungsten skeleton at high temperature under the vacuum condition followed by infiltration of copper. The effect of sintering temperature on microstructures and properties of the tungsten skeleton and the tungsten copper composite were investigated. The results show that with increasing of the sintering temperature, the point touch becomes face touch between tungsten particles; the sintering necks grow and the pores reduce to sphericity gradually. Meanwhile, the relative density and hardness of the tungsten skeleton and the tungsten copper composite increase constantly and the electric conductivity of the composite decreases correspondingly. When sintered at 1950 oC, the relative density of the tungsten skeleton and the tungsten copper composite reaches the maximum of 74.8% and 96.9%, respectively; the hardness (HB) of the tungsten copper composite gets the maximum of 2520 MPa, while its electrical conductivity reduces to 36.6IACS%; moreover, its oxygen content is only 4×10-6 and the nitrogen content is 3×10-6.
Tungsten copper composite for sputtering materials was fabricated by sintering a tungsten skeleton at high temperature under the vacuum condition followed by infiltration of copper. The effect of sintering temperature on microstructures and properties of the tungsten skeleton and the tungsten copper composite were investigated. The results show that with increasing of the sintering temperature, the point touch becomes face touch between tungsten particles; the sintering necks grow and the pores reduce to sphericity gradually. Meanwhile, the relative density and hardness of the tungsten skeleton and the tungsten copper composite increase constantly and the electric conductivity of the composite decreases correspondingly. When sintered at 1950 oC, the relative density of the tungsten skeleton and the tungsten copper composite reaches the maximum of 74.8% and 96.9%, respectively; the hardness (HB) of the tungsten copper composite gets the maximum of 2520 MPa, while its electrical conductivity reduces to 36.6IACS%; moreover, its oxygen content is only 4×10-6 and the nitrogen content is 3×10-6.
2010, 39(5):896-901.
Abstract:
WC powders with different particle sizes and ultrafine Co powders were mixed to form the initial powders. Afterwards ultrafine WC-Co cermet bulks were prepared by direct SPS and a new method combining vacuum pretreatment with SPS. Results show that the samples prepared by pretreatment and SPS have a little lower hardness but higher fracture toughness and much higher tensile strength than those by direct SPS. The analyses of microstructures and properties indicate that the vacuum pretreatment has important effect on the WC-Co cermets by SPS. It can release the adsorbed gas, cancel the “Co lake” and obtain completely densified bulks without significant grain growth.
WC powders with different particle sizes and ultrafine Co powders were mixed to form the initial powders. Afterwards ultrafine WC-Co cermet bulks were prepared by direct SPS and a new method combining vacuum pretreatment with SPS. Results show that the samples prepared by pretreatment and SPS have a little lower hardness but higher fracture toughness and much higher tensile strength than those by direct SPS. The analyses of microstructures and properties indicate that the vacuum pretreatment has important effect on the WC-Co cermets by SPS. It can release the adsorbed gas, cancel the “Co lake” and obtain completely densified bulks without significant grain growth.
32 Rapid Production of Bulk Al2O3/YAG/YSZ Ternary Eutectic Ceramic by Ultra-High-Gravity Melt-Casting
2010, 39(5):906-910.
Abstract:
A new method of rapid preparation for compact bulk Al2O3/YAG/YSZ ternary eutectic ceramics was researched. With Al/Fe2O3/Y2O3/ZrO2 as starting materials, the combustion synthesis reaction of Al/Fe2O3 was ignited, and then the molten compounds consisting of ceramics (Al2O3/YAG/YSZ) and metal (Fe) were achieved; afterwards the complete separation of ceramics melt from Fe melt and the solidification of the ceramics were realized under ultra-high-gravity field. The previously-solidified ceramics partially sank into the Fe melt, where the ceramics was forced to be entirely solidified by the instantaneous isostatic pressure on the verge of 2 MPa. The microstructure analysis results show that phase composition and morphology of grains of the obtained Al2O3/YAG/YSZ ternary eutectic ceramics have clearly gradient character along the ultra-high-gravity direction.
A new method of rapid preparation for compact bulk Al2O3/YAG/YSZ ternary eutectic ceramics was researched. With Al/Fe2O3/Y2O3/ZrO2 as starting materials, the combustion synthesis reaction of Al/Fe2O3 was ignited, and then the molten compounds consisting of ceramics (Al2O3/YAG/YSZ) and metal (Fe) were achieved; afterwards the complete separation of ceramics melt from Fe melt and the solidification of the ceramics were realized under ultra-high-gravity field. The previously-solidified ceramics partially sank into the Fe melt, where the ceramics was forced to be entirely solidified by the instantaneous isostatic pressure on the verge of 2 MPa. The microstructure analysis results show that phase composition and morphology of grains of the obtained Al2O3/YAG/YSZ ternary eutectic ceramics have clearly gradient character along the ultra-high-gravity direction.
2010, 39(5):911-914.
Abstract:
Laminated bimetal Al-Bi sheets were synthesized by thermo-physical temperature field hot-dip method. The Pb-Bi-Al laminated composite electrode materials were prepared by liquid-solid coating technique, and their microstructure and performance were characterized by linear scanning voltammetry (LSV), SEM and bending resistant measurement. The results show that the metallurgical bonding of the Pb-Al immiscible system is realized by the introduction of the third element of transition metal Bi. Compared with that of the conventional lead electrode, the bending strength of Pb-Bi-Al laminated composite electrode materials was increased by 33.7%, the mass was decreased by 11.0% and the electrode polarized potentials were reduced by 21.8%. In particular, it has a passivation current close to 0 in the polarized area. Therefore the Pb-Bi-Al laminated composite electrodes are excellent electrode materials with light mass, good conductivity, high strength and good corrosion resistance, and they have an important prospect of exploitation and utilization.
Laminated bimetal Al-Bi sheets were synthesized by thermo-physical temperature field hot-dip method. The Pb-Bi-Al laminated composite electrode materials were prepared by liquid-solid coating technique, and their microstructure and performance were characterized by linear scanning voltammetry (LSV), SEM and bending resistant measurement. The results show that the metallurgical bonding of the Pb-Al immiscible system is realized by the introduction of the third element of transition metal Bi. Compared with that of the conventional lead electrode, the bending strength of Pb-Bi-Al laminated composite electrode materials was increased by 33.7%, the mass was decreased by 11.0% and the electrode polarized potentials were reduced by 21.8%. In particular, it has a passivation current close to 0 in the polarized area. Therefore the Pb-Bi-Al laminated composite electrodes are excellent electrode materials with light mass, good conductivity, high strength and good corrosion resistance, and they have an important prospect of exploitation and utilization.
2010, 39(5):915-918.
Abstract:
A composite cathode material for Intermediate Temperature Solid Oxide Fuel Cells (IT-SOFC) was prepared by adding Ce0.8Sm0.2O1.9 into La0.7Sr0.3Co0.95Cu0.05O3-δ at different ratios. The crystal structure was characterized; the high temperature conductivity, thermal expansion coefficient and overpotentials of cathode electrodes were tested. The results show that adding Ce0.8Sm0.2O1.9 effectively decreases the thermal expansion coefficient of La0.7Sr0.3Co0.95Cu0.05O3-δ. When the content of the adding of Ce0.8Sm0.2O1.9 is 10% (mass faction, similarly hereinafter), the conductivity of the composite material is higher than that of La0.7Sr0.3Co0.95Cu0.05O3-δ and the current density of the cathode under the same overpotential is greater than that of others. A single fuel cell containing this cathode material has the maximum short-circuit current density of 511 mA/cm-2 and the maximum output power density of 106 mW /cm-2 at 850 °C.
A composite cathode material for Intermediate Temperature Solid Oxide Fuel Cells (IT-SOFC) was prepared by adding Ce0.8Sm0.2O1.9 into La0.7Sr0.3Co0.95Cu0.05O3-δ at different ratios. The crystal structure was characterized; the high temperature conductivity, thermal expansion coefficient and overpotentials of cathode electrodes were tested. The results show that adding Ce0.8Sm0.2O1.9 effectively decreases the thermal expansion coefficient of La0.7Sr0.3Co0.95Cu0.05O3-δ. When the content of the adding of Ce0.8Sm0.2O1.9 is 10% (mass faction, similarly hereinafter), the conductivity of the composite material is higher than that of La0.7Sr0.3Co0.95Cu0.05O3-δ and the current density of the cathode under the same overpotential is greater than that of others. A single fuel cell containing this cathode material has the maximum short-circuit current density of 511 mA/cm-2 and the maximum output power density of 106 mW /cm-2 at 850 °C.
2010, 39(5):924-927.
Abstract:
Vanadium nitride was synthesized by the microwave heating process with V2O5 (or ammonium metavanadate) as starting materials and carbon black as reductant in N2 atmosphere. The effects of the ratio of the carbon black to V2O5, nitridation temperature, nitridation time, N2 flux and the mixture pressure on the nitrogen content of the product were investigated when the reduction time was 60 min and the highest reduction temperature 933 K. Results show that the product of vanadium nitride has 12.6% nitrogen, 79.2% vanadium and 4.6% carbon and its density is 4.5 g/cm3, when the mixture pressure is 20 MPa, the ratio of carbon to V2O5 35%, nitridation time 120 min, nitridation temperature 1723 K and N2 flux 2 L/min. XRD patterns detect the product is pure vanadium nitride. Compared with the conventional resistance furnace heating method, the microwave heating process can shorten the time of reaction and cooling, save the energy, simplify the process and reduce the cost.
Vanadium nitride was synthesized by the microwave heating process with V2O5 (or ammonium metavanadate) as starting materials and carbon black as reductant in N2 atmosphere. The effects of the ratio of the carbon black to V2O5, nitridation temperature, nitridation time, N2 flux and the mixture pressure on the nitrogen content of the product were investigated when the reduction time was 60 min and the highest reduction temperature 933 K. Results show that the product of vanadium nitride has 12.6% nitrogen, 79.2% vanadium and 4.6% carbon and its density is 4.5 g/cm3, when the mixture pressure is 20 MPa, the ratio of carbon to V2O5 35%, nitridation time 120 min, nitridation temperature 1723 K and N2 flux 2 L/min. XRD patterns detect the product is pure vanadium nitride. Compared with the conventional resistance furnace heating method, the microwave heating process can shorten the time of reaction and cooling, save the energy, simplify the process and reduce the cost.
2010, 39(5):928-931.
Abstract:
The pure vanadium was prepared by hot isostatic pressing (HIPing). The mechanical properties of the pure vanadium were examined and the tensile fracture, microstructure and thermal change of the specimen were analyzed by a material testing machine, OM, SEM, TEM and TGA. The results show that pure vanadium can be up to full densification at the HIPing temperature above 1250 oC. With increasing of the temperature, the tensile strength and yield strength decreases at first and then increases, but the plasticity change is on the contrary. Its comprehensive mechanical properties are best at 1250 oC, e.g. the tensile and yield strength are 701 MPa and 634 MPa, respectively, and the elongation is up to 22.4%. Fracture of the specimens happens in the modes of slipping off or micro-porous aggregation. The grain sizes of pure vanadium prepared at different temperatures are similar, and lath-like martensite is observed in all of the specimens. The oxidation processes follow parabolic kinetics, whose activation energy is 118 kJ/mol.
The pure vanadium was prepared by hot isostatic pressing (HIPing). The mechanical properties of the pure vanadium were examined and the tensile fracture, microstructure and thermal change of the specimen were analyzed by a material testing machine, OM, SEM, TEM and TGA. The results show that pure vanadium can be up to full densification at the HIPing temperature above 1250 oC. With increasing of the temperature, the tensile strength and yield strength decreases at first and then increases, but the plasticity change is on the contrary. Its comprehensive mechanical properties are best at 1250 oC, e.g. the tensile and yield strength are 701 MPa and 634 MPa, respectively, and the elongation is up to 22.4%. Fracture of the specimens happens in the modes of slipping off or micro-porous aggregation. The grain sizes of pure vanadium prepared at different temperatures are similar, and lath-like martensite is observed in all of the specimens. The oxidation processes follow parabolic kinetics, whose activation energy is 118 kJ/mol.
2010, 39(5):932-935.
Abstract:
Praseodymium doped spinel LiPrxMn2-xO4 with single phase was synthesized by Sol-gel route. Its structure and electrochemical properties were studied by XRD, XPS and electrochemical measurements. The results show that when the doped Pr content is low (x≤0.02), the obtained product can maintain the whole spinel structure and exhibit excellent electrochemical properties. Pr3+ doping increases the cycle stability of the material greatly, which results from its stabilization for the spinel structure. The electrode of LiPr0.02Mn1.98O4 shows optimal electrochemical properties with a first discharge capacity of 118 mAh·g-1 and 98% of the initial capacity after 100 cycles at the current rate of 0.2 C. As cathode material of lithium-ion battery, this praseodymium doped spinel material is one of the most promising substitutes for LiCoO2.
Praseodymium doped spinel LiPrxMn2-xO4 with single phase was synthesized by Sol-gel route. Its structure and electrochemical properties were studied by XRD, XPS and electrochemical measurements. The results show that when the doped Pr content is low (x≤0.02), the obtained product can maintain the whole spinel structure and exhibit excellent electrochemical properties. Pr3+ doping increases the cycle stability of the material greatly, which results from its stabilization for the spinel structure. The electrode of LiPr0.02Mn1.98O4 shows optimal electrochemical properties with a first discharge capacity of 118 mAh·g-1 and 98% of the initial capacity after 100 cycles at the current rate of 0.2 C. As cathode material of lithium-ion battery, this praseodymium doped spinel material is one of the most promising substitutes for LiCoO2.
2010, 39(5):936-940.
Abstract:
Li-ion rechargeable batteries have been widely used as a reliable energy source for portable electronic devices, but the use in large power and high capacity, such as EV (Electrical Vehicle) and HEV (Hybrid Electrical Vehicle), is limited due to safety concerns associated with the thermal stability. In this paper, the influencing factors on the safety characteristics of Li-ion batteries were analyzed from the materials and the manufacturing process. The key safety problems of the Li-ion packs are further introduced.
Li-ion rechargeable batteries have been widely used as a reliable energy source for portable electronic devices, but the use in large power and high capacity, such as EV (Electrical Vehicle) and HEV (Hybrid Electrical Vehicle), is limited due to safety concerns associated with the thermal stability. In this paper, the influencing factors on the safety characteristics of Li-ion batteries were analyzed from the materials and the manufacturing process. The key safety problems of the Li-ion packs are further introduced.
