A novel nanopolycrystalline structure of vanadium dioxide thin films is deposited on silicon or fused silica substrates by reactive ion sputtering and followed by an annealing. The characteristic analysis＇shows that ...A novel nanopolycrystalline structure of vanadium dioxide thin films is deposited on silicon or fused silica substrates by reactive ion sputtering and followed by an annealing. The characteristic analysis＇shows that the films have a columnar nanostructure with an average grain of 8 nm. The resistivities as a function of ambient temperatures tested by four-point probes for as-deposited films present that the transition temperature for nanostructure of vanadium dioxide films is near 35 ℃ which lowers about 33 ℃ in comparison with the transition temperature at 68 ℃ in its microstructure.展开更多
Intermetallic compounds have the characteristics of long-range ordered structure and combination of metallic and covalent bonds,showing intrinsic brittleness and outstanding performance stability.The synthesis mechani...Intermetallic compounds have the characteristics of long-range ordered structure and combination of metallic and covalent bonds,showing intrinsic brittleness and outstanding performance stability.The synthesis mechanism,pore structure characterization and material properties of powder metallurgy porous intermetallics are reviewed in this paper.Compared with traditional porous materials,porous intermetallics have good thermal impact resistance,machinability,thermal and electrical conductivity similar to metals,as well as good chemical corrosion resistance,rigidity and high-temperature property similar to ceramics.The mechanisms of preparation and pore formation of porous intermetallics mainly include four aspects:(1)the physical process based on the interstitial space between the initial particles and its evolution in the subsequent procedures;(2)the chemical combustion process based on the violent reaction between the initial powder components;(3)the reaction kinetics process based on the difference between the diffusion rates of elements;(4)the phase transition process based on the difference between the phase densities.The characterization parameters to the pore structure description for porous intermetallics include mainly overall porosity,open porosity,permeability,maximum pore size,pore size distribution and tortuosity factor.In terms of microstructure characterization of porous intermetallics,three-dimensional pore morphology scanning technology has the potential to reveal the internal characteristics of pore structures.The research on material properties of porous intermetallics mainly focuses on electrochemical catalytic activity,generalized oxidation resistivity at high temperature,resistance against chemical corrosion and mechanical properties,which have obvious advantages over traditional porous materials.In the field of the development of porous intermetallics,it is expected to expand their applications by further reducing the pore size to the nanoscale level to improve the filtration accuracy or increase the specific surface area,as well as introducing the high entropy design on the composition to improve the brittleness and enhance their material performance.展开更多
A series of nanometer oxide catalytic materials AMyAl12-yO19-δwere prepared by roasting solid oxides from the decomposition of nitrates.Its crystal structure and properties were characterized by XRD,BET,TEM technique...A series of nanometer oxide catalytic materials AMyAl12-yO19-δwere prepared by roasting solid oxides from the decomposition of nitrates.Its crystal structure and properties were characterized by XRD,BET,TEM techniques,and the catalytic activities for CO2 reforming of methane to synthetic gas was also investigated.Experimental results showed that AMyAl12-yO19-δ exhibited similar crystal structures and different properties due to the difference of the substituted metals A and M.Under the same reaction condition,compound oxides AMyAl12-yO19-δexhibited significant catalytic activities and stability for CO2 reforming of methane.During 18h reaction at 700℃,the conversions of CH4 and CO2 remained over 93.4%and 91.2%,respectively and the amount of carbon deposited was only 1.57%.展开更多
基金This research work was supported by the National Nature Science Foundation of China under Grant No. 60477040.
文摘A novel nanopolycrystalline structure of vanadium dioxide thin films is deposited on silicon or fused silica substrates by reactive ion sputtering and followed by an annealing. The characteristic analysis＇shows that the films have a columnar nanostructure with an average grain of 8 nm. The resistivities as a function of ambient temperatures tested by four-point probes for as-deposited films present that the transition temperature for nanostructure of vanadium dioxide films is near 35 ℃ which lowers about 33 ℃ in comparison with the transition temperature at 68 ℃ in its microstructure.
基金the National Natural Science Foundation of China (No. 51971251, 51774336)。
文摘Intermetallic compounds have the characteristics of long-range ordered structure and combination of metallic and covalent bonds,showing intrinsic brittleness and outstanding performance stability.The synthesis mechanism,pore structure characterization and material properties of powder metallurgy porous intermetallics are reviewed in this paper.Compared with traditional porous materials,porous intermetallics have good thermal impact resistance,machinability,thermal and electrical conductivity similar to metals,as well as good chemical corrosion resistance,rigidity and high-temperature property similar to ceramics.The mechanisms of preparation and pore formation of porous intermetallics mainly include four aspects:(1)the physical process based on the interstitial space between the initial particles and its evolution in the subsequent procedures;(2)the chemical combustion process based on the violent reaction between the initial powder components;(3)the reaction kinetics process based on the difference between the diffusion rates of elements;(4)the phase transition process based on the difference between the phase densities.The characterization parameters to the pore structure description for porous intermetallics include mainly overall porosity,open porosity,permeability,maximum pore size,pore size distribution and tortuosity factor.In terms of microstructure characterization of porous intermetallics,three-dimensional pore morphology scanning technology has the potential to reveal the internal characteristics of pore structures.The research on material properties of porous intermetallics mainly focuses on electrochemical catalytic activity,generalized oxidation resistivity at high temperature,resistance against chemical corrosion and mechanical properties,which have obvious advantages over traditional porous materials.In the field of the development of porous intermetallics,it is expected to expand their applications by further reducing the pore size to the nanoscale level to improve the filtration accuracy or increase the specific surface area,as well as introducing the high entropy design on the composition to improve the brittleness and enhance their material performance.
文摘A series of nanometer oxide catalytic materials AMyAl12-yO19-δwere prepared by roasting solid oxides from the decomposition of nitrates.Its crystal structure and properties were characterized by XRD,BET,TEM techniques,and the catalytic activities for CO2 reforming of methane to synthetic gas was also investigated.Experimental results showed that AMyAl12-yO19-δ exhibited similar crystal structures and different properties due to the difference of the substituted metals A and M.Under the same reaction condition,compound oxides AMyAl12-yO19-δexhibited significant catalytic activities and stability for CO2 reforming of methane.During 18h reaction at 700℃,the conversions of CH4 and CO2 remained over 93.4%and 91.2%,respectively and the amount of carbon deposited was only 1.57%.
