Scandia and rhenium doped tungsten powders were prepared by solid-liquid doping combined with two-step reduction method. The particle size of doped tungsten and distribution of scandia and rhenium were studied by SEM,...Scandia and rhenium doped tungsten powders were prepared by solid-liquid doping combined with two-step reduction method. The particle size of doped tungsten and distribution of scandia and rhenium were studied by SEM, EDS, XRD and granularity analysis. Experimental results showed that scandia distributed evenly on the surface of tungsten particles. Addition of scandia and rhenium decreased the particle size of doped tungsten, and the more the content of scandia and rhenium, the smaller the doped tungsten particles. Tungsten powders doped with 3 % Sc2O3 and 3 % Re （mass fraction） had an average size of about 80 nm in diameter. The mechanism of the decrease in the tungsten particle size was discussed.展开更多
As a matrix for Sc-type impregnated cathode,scandia doped tungsten with a uniform distribution of Sc2O3 was obtained by powder metallurgy combined with the liquid-solid doping method.The microstructure and composition...As a matrix for Sc-type impregnated cathode,scandia doped tungsten with a uniform distribution of Sc2O3 was obtained by powder metallurgy combined with the liquid-solid doping method.The microstructure and composition of the powder and the anti-ion bombardment behavior of scandium in the matrix were studied by means of SEM,EDS,XRD,and in-situ AES methods.Tungsten powder covered with scandium oxide,an ideal scandium oxide-doped tungsten powder for the preparation of Sc-type impregnated cathode,was obtained using the liquid-solid doping method.Compared with the matrix prepared with the mechanically mixed powder of tungsten and scandium oxide,Sc2O3-W matrix prepared with this kind of powder had smaller grain size and uniform distribution of scandium.Sc on the surface of Sc2O3 doped tungsten matrix had good high temperature stability and good anti-ion bombardment capability.展开更多
Scandia stabilized zirconia powder （ScSZ） was first synthesized by a microwave-hydrothermal method. The crystalline and aggregated particle sizes were investigated by means of X-ray diffraction （XRD）, Raman, scann...Scandia stabilized zirconia powder （ScSZ） was first synthesized by a microwave-hydrothermal method. The crystalline and aggregated particle sizes were investigated by means of X-ray diffraction （XRD）, Raman, scanning electron microscopy （SEM） and transmission electron microscopy （TEM）. Weakly agglomerated and well crystallized ScSZ powder was prepared by microwave-heating to 150 ℃ and 2.5 h. The structure of the ScSZ powder changed from a tetragonal to a cubic phase, and accordingly, the powder conductivity was increased from 90.55 to 120.56 ms/cm by the introduction of the mineralizer solutions （KOH＋K2CO3） during the microwave-hydrothermal processing.展开更多
Scandia doped tungsten powders were prepared by spray drying combined with two-step hydrogen reduction.The particle size of doped tungsten powder,powder morphology and doped tungsten matrix were characterized by scann...Scandia doped tungsten powders were prepared by spray drying combined with two-step hydrogen reduction.The particle size of doped tungsten powder,powder morphology and doped tungsten matrix were characterized by scanning electron microscope,X-ray diffrac-tion and laser diffraction particle size analyzer,respectively.The reduction behavior of Sc2O3 doped tungsten oxide and the effect of Sc2O3 on the property of tungsten powder were studied by the temperature programmed reduction.The experimental results showed that the pre-cursor powders prepared by spray drying had spherical shape.The addition of Sc2O3 could decrease the reduction temperature of tungsten oxide.The scandia doped tungsten powder had sub-micrometer size in the range of 0.1 to1 μm and scandium distributed evenly in the powder.By using this kind powder,sub-microstructure cathode matrices with semispherical grains and homogenous distribution of scan-dium were obtained.展开更多
Scandia pressed cathodes were prepared by powder metallurgy method using mixed powder of scandia doped tungsten and barium-calcium aluminates obtained by different mixing methods.The element distribution uniformity gr...Scandia pressed cathodes were prepared by powder metallurgy method using mixed powder of scandia doped tungsten and barium-calcium aluminates obtained by different mixing methods.The element distribution uniformity greatly affected the emission property.The powder prepared by ball-milling had small particle size and uniform distribution of different elements.This kind of powder was favorable for the chemical reaction among Ba,Ca aluminates,scandia and tungsten to take place sufficiently to form active substance which can improve the emission property.The emission current density of the cathode prepared with ball-milling powder was about 8 times higher than that prepared by manually mixing method,4 times higher than Os coated M-type cathode.The higher content of the active substance on the cathode surface prepared by ball-milling led to the better emission performance of the cathode.展开更多
As an important powder material for scandate cathode,Sc_(2) O_(3)-doped WO_(3) powder together with hollow spherical WO_(3) for comparison was prepared by spraydrying method.The reduction behavior and kinetics of pure...As an important powder material for scandate cathode,Sc_(2) O_(3)-doped WO_(3) powder together with hollow spherical WO_(3) for comparison was prepared by spraydrying method.The reduction behavior and kinetics of pure WO_(3) and Sc_(2) O_(3)-doped WO_(3) were studied by temperatureprogrammed reduction(TPR) method.It is found that scandia doping can decrease the reduction activation energy of WO_(3) and thus lower the reduction temperature and increase the reduction rate.Based on the kinetics results,the reduction techniques are presented.The obtained powder has a narrow size distribution in the range of 0.6-0.8 μm.展开更多
Ultrafine powders of scandia-stabilized zirconia (ScSZ) were prepared by the co-precipitation method, using ZrOCl2 and ScO2 as raw materials and NH3·H2O as a precipitant. In this paper, the optimum process parame...Ultrafine powders of scandia-stabilized zirconia (ScSZ) were prepared by the co-precipitation method, using ZrOCl2 and ScO2 as raw materials and NH3·H2O as a precipitant. In this paper, the optimum process parameters were investigated. The pH of the reaction solution directly impacted the precursor structure, which further affected the obtained crystal forming. Many experiment methods of thermogravimetric analysis and differential thermal analysis (TG-DTA), X-ray diffraction (XRD), transmission electron microscopy (TEM), Raman spectroscopy (Raman), and nitrogen adsorption were employed to characterize the ScSZ powder. The structure transition mechanism from cubic to rhombohedral was discussed. In addition, the electrical conductivity of the powders was also studied after dry-pressing and calcining. The results showed that the structure of ScSZ with complete crystal surface belonged to the cubic phase. The crystallite sizes of the powders prepared are about 60–80 nm, meet the conditions of (D90–D10)/2D50≤1, and ex-hibited the good flow properties. The electrical conductivity was more than 190 mS/cm in air measured at 850 oC.展开更多
Homogeneous (ZrO_2)_(0.92)(Sc_2O_3)_(0.08) solid solution in fluorite cubic structure was prepared from the gels with altered molar ratios of citric acid (CA) to metal ions (M) and ethylene glycol (EG) via a polymeriz...Homogeneous (ZrO_2)_(0.92)(Sc_2O_3)_(0.08) solid solution in fluorite cubic structure was prepared from the gels with altered molar ratios of citric acid (CA) to metal ions (M) and ethylene glycol (EG) via a polymerization route (Pechini method). Due to the enhanced chemical homogeneity (high level of mixing of metal ions and ligands) in the polymeric gels, Sc-doped zirconia can be crystallized at temperatures as low as 400 ℃. During the evolution from amorphous gel to the crystallized (ZrO_2)_(0.92)(Sc_2O_3)_(0.08) fine powder, the bonding nature between carboxylate groups and Zr/Sc cations changed: unidentate→bridging→ionic upon calcination. The molar ratios of CA/M (1～4) and CA/EG (0.2～4) were demonstrated to affect the thermal behavior of the gels and thus the particle properties of the derived nanoparticulate oxide powders (including particle size and surface area). The as-sintered sample compacted from the nanosized powders prepared by calcining the gel with the highest content of organics (CA/M=4 and CA/EG=0.2) exhibited the best sinterability and the highest oxide ion conductivity.展开更多
基金Project supported by the National Natural Science Foundation of China (50571001)the National "863"Project(2006AA03Z524)
文摘Scandia and rhenium doped tungsten powders were prepared by solid-liquid doping combined with two-step reduction method. The particle size of doped tungsten and distribution of scandia and rhenium were studied by SEM, EDS, XRD and granularity analysis. Experimental results showed that scandia distributed evenly on the surface of tungsten particles. Addition of scandia and rhenium decreased the particle size of doped tungsten, and the more the content of scandia and rhenium, the smaller the doped tungsten particles. Tungsten powders doped with 3 % Sc2O3 and 3 % Re （mass fraction） had an average size of about 80 nm in diameter. The mechanism of the decrease in the tungsten particle size was discussed.
基金supported by the Program for New Century Excellent Talents in Universities,the National High Technology Research and Development Program of China(No.2006AA03Z524)the National Natural Science Foundation of China(No.50571001).
文摘As a matrix for Sc-type impregnated cathode,scandia doped tungsten with a uniform distribution of Sc2O3 was obtained by powder metallurgy combined with the liquid-solid doping method.The microstructure and composition of the powder and the anti-ion bombardment behavior of scandium in the matrix were studied by means of SEM,EDS,XRD,and in-situ AES methods.Tungsten powder covered with scandium oxide,an ideal scandium oxide-doped tungsten powder for the preparation of Sc-type impregnated cathode,was obtained using the liquid-solid doping method.Compared with the matrix prepared with the mechanically mixed powder of tungsten and scandium oxide,Sc2O3-W matrix prepared with this kind of powder had smaller grain size and uniform distribution of scandium.Sc on the surface of Sc2O3 doped tungsten matrix had good high temperature stability and good anti-ion bombardment capability.
基金Project supported by National Science and Technology Support Project of China(2012BAB10B11)Rare-earth Adjustment Up grade Projects of Ministry of Industry and Information Technology of China
文摘Scandia stabilized zirconia powder （ScSZ） was first synthesized by a microwave-hydrothermal method. The crystalline and aggregated particle sizes were investigated by means of X-ray diffraction （XRD）, Raman, scanning electron microscopy （SEM） and transmission electron microscopy （TEM）. Weakly agglomerated and well crystallized ScSZ powder was prepared by microwave-heating to 150 ℃ and 2.5 h. The structure of the ScSZ powder changed from a tetragonal to a cubic phase, and accordingly, the powder conductivity was increased from 90.55 to 120.56 ms/cm by the introduction of the mineralizer solutions （KOH＋K2CO3） during the microwave-hydrothermal processing.
基金Project supported by Beijing Natural Science Foundation (2102007)Program for Excellent Talents in Beijing (PHR201006101)National Nature Science funding (51071005)
文摘Scandia doped tungsten powders were prepared by spray drying combined with two-step hydrogen reduction.The particle size of doped tungsten powder,powder morphology and doped tungsten matrix were characterized by scanning electron microscope,X-ray diffrac-tion and laser diffraction particle size analyzer,respectively.The reduction behavior of Sc2O3 doped tungsten oxide and the effect of Sc2O3 on the property of tungsten powder were studied by the temperature programmed reduction.The experimental results showed that the pre-cursor powders prepared by spray drying had spherical shape.The addition of Sc2O3 could decrease the reduction temperature of tungsten oxide.The scandia doped tungsten powder had sub-micrometer size in the range of 0.1 to1 μm and scandium distributed evenly in the powder.By using this kind powder,sub-microstructure cathode matrices with semispherical grains and homogenous distribution of scan-dium were obtained.
基金Project supported by the National Natural Science Foundation of China (51071005)Beijing Natural Science Foundation (2102007)Program for Excellent Talents in Beijing (PHR201006101)
文摘Scandia pressed cathodes were prepared by powder metallurgy method using mixed powder of scandia doped tungsten and barium-calcium aluminates obtained by different mixing methods.The element distribution uniformity greatly affected the emission property.The powder prepared by ball-milling had small particle size and uniform distribution of different elements.This kind of powder was favorable for the chemical reaction among Ba,Ca aluminates,scandia and tungsten to take place sufficiently to form active substance which can improve the emission property.The emission current density of the cathode prepared with ball-milling powder was about 8 times higher than that prepared by manually mixing method,4 times higher than Os coated M-type cathode.The higher content of the active substance on the cathode surface prepared by ball-milling led to the better emission performance of the cathode.
基金financially supported by the National Key Research and Development Program of China(Nos.2017YFA0701000 and 2016YFE0126900)the National Natural Science Foundation of China(Nos.51471006,51534009 and52621003)the Fundamental Research Funds for the Central Universities(Nos.ZYGX2018J024 and ZYGX2015Z010)。
文摘As an important powder material for scandate cathode,Sc_(2) O_(3)-doped WO_(3) powder together with hollow spherical WO_(3) for comparison was prepared by spraydrying method.The reduction behavior and kinetics of pure WO_(3) and Sc_(2) O_(3)-doped WO_(3) were studied by temperatureprogrammed reduction(TPR) method.It is found that scandia doping can decrease the reduction activation energy of WO_(3) and thus lower the reduction temperature and increase the reduction rate.Based on the kinetics results,the reduction techniques are presented.The obtained powder has a narrow size distribution in the range of 0.6-0.8 μm.
基金supported by the National Science and Technology Support Project of China(2012BAB10B00)Rare-Earth Adjustment Upgrade Projects of Ministry of Industry and Information Technology of PRC
文摘Ultrafine powders of scandia-stabilized zirconia (ScSZ) were prepared by the co-precipitation method, using ZrOCl2 and ScO2 as raw materials and NH3·H2O as a precipitant. In this paper, the optimum process parameters were investigated. The pH of the reaction solution directly impacted the precursor structure, which further affected the obtained crystal forming. Many experiment methods of thermogravimetric analysis and differential thermal analysis (TG-DTA), X-ray diffraction (XRD), transmission electron microscopy (TEM), Raman spectroscopy (Raman), and nitrogen adsorption were employed to characterize the ScSZ powder. The structure transition mechanism from cubic to rhombohedral was discussed. In addition, the electrical conductivity of the powders was also studied after dry-pressing and calcining. The results showed that the structure of ScSZ with complete crystal surface belonged to the cubic phase. The crystallite sizes of the powders prepared are about 60–80 nm, meet the conditions of (D90–D10)/2D50≤1, and ex-hibited the good flow properties. The electrical conductivity was more than 190 mS/cm in air measured at 850 oC.
文摘Homogeneous (ZrO_2)_(0.92)(Sc_2O_3)_(0.08) solid solution in fluorite cubic structure was prepared from the gels with altered molar ratios of citric acid (CA) to metal ions (M) and ethylene glycol (EG) via a polymerization route (Pechini method). Due to the enhanced chemical homogeneity (high level of mixing of metal ions and ligands) in the polymeric gels, Sc-doped zirconia can be crystallized at temperatures as low as 400 ℃. During the evolution from amorphous gel to the crystallized (ZrO_2)_(0.92)(Sc_2O_3)_(0.08) fine powder, the bonding nature between carboxylate groups and Zr/Sc cations changed: unidentate→bridging→ionic upon calcination. The molar ratios of CA/M (1～4) and CA/EG (0.2～4) were demonstrated to affect the thermal behavior of the gels and thus the particle properties of the derived nanoparticulate oxide powders (including particle size and surface area). The as-sintered sample compacted from the nanosized powders prepared by calcining the gel with the highest content of organics (CA/M=4 and CA/EG=0.2) exhibited the best sinterability and the highest oxide ion conductivity.
