A critical examination was made on the reliability of kinetic parameters of nonisothermal thermoanalytical rate measurement by the widely applied Coats-Redfern(CR)equation.For this purpose,simulated TGA curves were ma...A critical examination was made on the reliability of kinetic parameters of nonisothermal thermoanalytical rate measurement by the widely applied Coats-Redfern(CR)equation.For this purpose,simulated TGA curves were made for reactions with different kinetic models,including chemical,diffusion(Janders)and mixed mechanism at different heating rates.The results show that,for reactions controlled kinetically by one mechanism,all solid state reaction models show linear trends by use of CR method and this method can not distinct the correct reaction model.For reactions with mixed mechanism,the CR method shows nonlinear trends and the reaction models and kinetic parameters can not be extracted from CR curves.The overall conclusion from this comparative appraisal of the characteristics of the CR approach to kinetic analysis of TGA data is that the CR approach is generally unsuitable for determination of kinetic parameters.展开更多
The environmental risk of chromium pollution is pronounced in soils adjacent to chromate industry. It is important to investigate the functioning of soil microorganisms in ecosystems exposed to long-term contamination...The environmental risk of chromium pollution is pronounced in soils adjacent to chromate industry. It is important to investigate the functioning of soil microorganisms in ecosystems exposed to long-term contamination by chromium. 45 soil samples obtained from different places of the slag heap in a steel alloy factory were analyzed for chromium contamination level and its effect on soil microorganisms and enzyme activities. The results show that the average concentrations of total Cr in the soil under the slag heap, adjacent to the slag heap and outside the factory exceed the threshold of Secondary Environmental Quality Standard for Soil in China by 354%, 540% and 184%, respectively, and are 15, 21 and 9 times higher than the local background value, respectively. Elevated chromium loadings result in changes in the activity of the soil microbe, as indicated by the negative correlations between soil microbial population and chromium contents. Dehydrogenase activity is greatly depressed by chromium in the soil. The results imply that dehydrogenase activity can be used as an indicator for the chromium pollution level in the area of the steel alloy factory.展开更多
Based on the process experiments, micrography analysis was dedicated to advancing the understanding of plastic flow of the metal in backward ball spinning of thin-walled tubular part with longitudinal inner ribs. Micr...Based on the process experiments, micrography analysis was dedicated to advancing the understanding of plastic flow of the metal in backward ball spinning of thin-walled tubular part with longitudinal inner ribs. Micrography analysis reveals that severe plastic deformation leads to grain refinement, grain orientation and grain flow line of the spun part. Based on rigid-plastic finite element method, DEFORME3D finite element code was used to simulate and analyze multi-pass backward ball spinning of thin-walled tubular part with longitudinal inner ribs. Finite element simulation results involve the distributions of the strain, the shape variation of the inner ribs as well as the prediction of the spinning loading.展开更多
Hot deformation behaviors of TC11 alloy with β-annealed lamellar structure and forged equiaxed structure were investigated in the β field in the temperature range of 1 090-1 030 ℃ and strain rate of 0.001-0.1 s-1 b...Hot deformation behaviors of TC11 alloy with β-annealed lamellar structure and forged equiaxed structure were investigated in the β field in the temperature range of 1 090-1 030 ℃ and strain rate of 0.001-0.1 s-1 by means of isothermal compression tests.Hot deformation characteristics and microstructure evolutions of the two starting structures were analyzed.And hot processing power dissipation efficiency maps were established.EBSD technique was used for testing grain boundary characteristic of deformation structures.The results indicate that hot deformation mechanism of TC11 alloy in β field is dynamic recovery accompanied by geometric dynamic recrystallization at large strains,or discontinuous dynamic recrystallization based on the starting structure states and deformation parameters.Accordingly,there are two different grain refining patterns.One is characteristic of new fine grains in the interior of elongated prior β grains that have serrated grain boundaries; and the other is that of new fine grains along elongated prior β grain boundaries.展开更多
A Li2FeSiO4/C composite cathode for lithium ion batteries was synthesized at 650 ℃ by solid-state reaction. The effects of carbon sources and carbon content on the properties of the Li2FeSiO4/C composites were invest...A Li2FeSiO4/C composite cathode for lithium ion batteries was synthesized at 650 ℃ by solid-state reaction. The effects of carbon sources and carbon content on the properties of the Li2FeSiO4/C composites were investigated. The crystalline structure, morphology, carbon content and charge/discharge performance of Li2FeSiO4/C composites were determined by X-ray diffraction(XRD), scanning electron microscopy(SEM), carbon/sulfur analyzer and electrochemical measurements. As carbon content increases in the range of 5%?20%, the amount of Fe3O4 impurity phase decreases. The SEM micrographs show that the addition of the carbon is favorable for reducing the Li2FeSiO4 grain size. Using sucrose as carbon source, the Li2FeSiO4/C composite with 14.5% carbon synthesized at 650 ℃ shows good electrochemical performance with an initial discharge capacity of 144.8 mA·h/g and a capacity retention ratio of 94.27% after 13 cycles.展开更多
The microstructure of an AA 7B04 alloy in the form of plate was investigated using differential scanning calorimetry(DSC)and TEM analysis technologies.Tensile properties and electrical conductivity of AA 7B04 under va...The microstructure of an AA 7B04 alloy in the form of plate was investigated using differential scanning calorimetry(DSC)and TEM analysis technologies.Tensile properties and electrical conductivity of AA 7B04 under various heat treatment conditions were also presented.The results reveal that peak-aged microstructure contains GP zones and η' precipitates predominantly.After retrogressing and reaging(RRA),the η' and η precipitates disperse in the alloy matrix,and the η precipitates distribute coarsely and sparsely,decorating the grain boundaries,together with precipitate free zones(PFZs)around them.It is also shown that selecting of suitable heat treatments can provide optimal precipitates in matrix and at grain boundaries,which gives rise to a combination of high strength and stress corrosion cracking(SCC)resistance in such materials.展开更多
文摘A critical examination was made on the reliability of kinetic parameters of nonisothermal thermoanalytical rate measurement by the widely applied Coats-Redfern(CR)equation.For this purpose,simulated TGA curves were made for reactions with different kinetic models,including chemical,diffusion(Janders)and mixed mechanism at different heating rates.The results show that,for reactions controlled kinetically by one mechanism,all solid state reaction models show linear trends by use of CR method and this method can not distinct the correct reaction model.For reactions with mixed mechanism,the CR method shows nonlinear trends and the reaction models and kinetic parameters can not be extracted from CR curves.The overall conclusion from this comparative appraisal of the characteristics of the CR approach to kinetic analysis of TGA data is that the CR approach is generally unsuitable for determination of kinetic parameters.
基金Project(K0802144-31) supported by the Program of Science and Technology of Changsha, ChinaProjects(2006AA06Z374, 2007AA021304) supported by the National Hi-tech Research and Development Program of China
文摘The environmental risk of chromium pollution is pronounced in soils adjacent to chromate industry. It is important to investigate the functioning of soil microorganisms in ecosystems exposed to long-term contamination by chromium. 45 soil samples obtained from different places of the slag heap in a steel alloy factory were analyzed for chromium contamination level and its effect on soil microorganisms and enzyme activities. The results show that the average concentrations of total Cr in the soil under the slag heap, adjacent to the slag heap and outside the factory exceed the threshold of Secondary Environmental Quality Standard for Soil in China by 354%, 540% and 184%, respectively, and are 15, 21 and 9 times higher than the local background value, respectively. Elevated chromium loadings result in changes in the activity of the soil microbe, as indicated by the negative correlations between soil microbial population and chromium contents. Dehydrogenase activity is greatly depressed by chromium in the soil. The results imply that dehydrogenase activity can be used as an indicator for the chromium pollution level in the area of the steel alloy factory.
基金Project(3236301154) supported by Postdoctoral Foundation of Heilongjiang Province, China
文摘Based on the process experiments, micrography analysis was dedicated to advancing the understanding of plastic flow of the metal in backward ball spinning of thin-walled tubular part with longitudinal inner ribs. Micrography analysis reveals that severe plastic deformation leads to grain refinement, grain orientation and grain flow line of the spun part. Based on rigid-plastic finite element method, DEFORME3D finite element code was used to simulate and analyze multi-pass backward ball spinning of thin-walled tubular part with longitudinal inner ribs. Finite element simulation results involve the distributions of the strain, the shape variation of the inner ribs as well as the prediction of the spinning loading.
文摘Hot deformation behaviors of TC11 alloy with β-annealed lamellar structure and forged equiaxed structure were investigated in the β field in the temperature range of 1 090-1 030 ℃ and strain rate of 0.001-0.1 s-1 by means of isothermal compression tests.Hot deformation characteristics and microstructure evolutions of the two starting structures were analyzed.And hot processing power dissipation efficiency maps were established.EBSD technique was used for testing grain boundary characteristic of deformation structures.The results indicate that hot deformation mechanism of TC11 alloy in β field is dynamic recovery accompanied by geometric dynamic recrystallization at large strains,or discontinuous dynamic recrystallization based on the starting structure states and deformation parameters.Accordingly,there are two different grain refining patterns.One is characteristic of new fine grains in the interior of elongated prior β grains that have serrated grain boundaries; and the other is that of new fine grains along elongated prior β grain boundaries.
基金Project(2007CB613607) supported by the National Basic Research Program of China
文摘A Li2FeSiO4/C composite cathode for lithium ion batteries was synthesized at 650 ℃ by solid-state reaction. The effects of carbon sources and carbon content on the properties of the Li2FeSiO4/C composites were investigated. The crystalline structure, morphology, carbon content and charge/discharge performance of Li2FeSiO4/C composites were determined by X-ray diffraction(XRD), scanning electron microscopy(SEM), carbon/sulfur analyzer and electrochemical measurements. As carbon content increases in the range of 5%?20%, the amount of Fe3O4 impurity phase decreases. The SEM micrographs show that the addition of the carbon is favorable for reducing the Li2FeSiO4 grain size. Using sucrose as carbon source, the Li2FeSiO4/C composite with 14.5% carbon synthesized at 650 ℃ shows good electrochemical performance with an initial discharge capacity of 144.8 mA·h/g and a capacity retention ratio of 94.27% after 13 cycles.
基金Project(G2003AA331100)supported by the National High-Tech Research Development Program of China
文摘The microstructure of an AA 7B04 alloy in the form of plate was investigated using differential scanning calorimetry(DSC)and TEM analysis technologies.Tensile properties and electrical conductivity of AA 7B04 under various heat treatment conditions were also presented.The results reveal that peak-aged microstructure contains GP zones and η' precipitates predominantly.After retrogressing and reaging(RRA),the η' and η precipitates disperse in the alloy matrix,and the η precipitates distribute coarsely and sparsely,decorating the grain boundaries,together with precipitate free zones(PFZs)around them.It is also shown that selecting of suitable heat treatments can provide optimal precipitates in matrix and at grain boundaries,which gives rise to a combination of high strength and stress corrosion cracking(SCC)resistance in such materials.
