High purity vanadium nitride(VN)powders were prepared via a two-step process using vanadium trioxide(V2 O3)as the raw material.The V2 O3 was firstly reduced at 873 K in Ar atmosphere via magnesiothermic reduction reac...High purity vanadium nitride(VN)powders were prepared via a two-step process using vanadium trioxide(V2 O3)as the raw material.The V2 O3 was firstly reduced at 873 K in Ar atmosphere via magnesiothermic reduction reaction to get the mixture of V and MgO,and then the products were further nitrided at 1473 K in N2 atmosphere.Finally,the as-prepared samples were acid-leached to obtain pure VN powders.X-ray diffractometry and field-emission scanning electron microscopy were used to analyze the phase transition and morphological evolution of the samples.The results reveal that the overall morphology of the obtained VN powder retains the morphology of the initial V2 O3 powders.After removing MgO by acidic leaching,the porous VN particles can be obtained,with the oxygen content of 0.178 wt.%.Compared with the traditional methods,high purity VN powders with a small amount of oxygen and no carbon can be obtained.展开更多
Sialon ceramics were prepared by the nitridation of Si,Al and Al2O3 powders with the transition metals(Fe Co,Ni)catalysts.The phase composition,microstructure and mechanical properties of specimens were studied Compar...Sialon ceramics were prepared by the nitridation of Si,Al and Al2O3 powders with the transition metals(Fe Co,Ni)catalysts.The phase composition,microstructure and mechanical properties of specimens were studied Compared with the catalyst-free specimen,the addition of Fe,Co and Ni greatly promoted the nitridation process of Sialon ceramics and improved the weight gain rate and mechanical properties of specimens.With the increased content of catalysts,the apparent porosity of the products decreased first and then increased,contrary to flexural strength and compressive strength.The specimen with 2.5 wt%Fe had the highest flexural strength 145.8 MPa and it exhibited the highest compressive strength of 594.6 MPa when Co content was 2.5 wt%,whereas they were 71.9 and 78.7 MPa,respectively,when without catalyst.展开更多
β-Sialon/ZrN bonded corundum composites were synthesized using fused white corundum,alumina micro powder,zircon and carbon black by nitridation reaction sintering process. Phase composition and microstructure of the ...β-Sialon/ZrN bonded corundum composites were synthesized using fused white corundum,alumina micro powder,zircon and carbon black by nitridation reaction sintering process. Phase composition and microstructure of the synthesized composites were investigated by X-ray powder diffraction and scanning electronic microscope,and the formation process of the composites was discussed. The results show that the composites with different compositions can be obtained by controlling the heating temperature and contents of zircon and carbon black. The proper temperature to synthesize the composites is 1773 K.展开更多
Nanoparticles of refractory compounds represent a class of stable materials showing a great promise to support localized surface plasmon resonances(LSPRs)in both visible and near infrared(NIR)spectral regions.It is st...Nanoparticles of refractory compounds represent a class of stable materials showing a great promise to support localized surface plasmon resonances(LSPRs)in both visible and near infrared(NIR)spectral regions.It is still challenging to rationally tune the LSPR band because of the difficulty to control the density of charge carriers in individual refractory nanoparticles and maintain the dispersity of nanoparticles in the processes of synthesis and applications.In this work,controlled chemical transformation of titanium dioxide(TiO_(2))nanoparticles encapsulated with mesoporous silica(SiO_(2))shells to titanium nitride(TiN)via nitridation reaction at elevated temperatures is developed to tune the density of free electrons in the resulting titanium-oxide-nitride(TiO_(x)N_(y))nanoparticles.Such tunability enables a flexibility to support LSPR-based optical absorption in the synthesized TiO_(x)N_(y)@SiO_(2) core-shell nanoparticles across both the visible and NIR regions.The silica shells play a crucial role in preventing the sintering of TiO_(x)N_(y) nanoparticles in the nitridation reaction and maintaining the stability of TiOxNy nanoparticles in applications.The LSPR-based broadband absorption of light in the TiO_(x)N_(y)@SiO_(2) nanoparticles exhibits strong photothermal effect with photo-to-thermal conversion efficiency as high as〜76%.展开更多
A novel method was used to fabricate AlN coating on graphite substrate. This approach included two steps： firstly, the emulsion composed of BN and anhydrous ethanol was sprayed on the surface of the graphite substrat...A novel method was used to fabricate AlN coating on graphite substrate. This approach included two steps： firstly, the emulsion composed of BN and anhydrous ethanol was sprayed on the surface of the graphite substrate; secondly, AlN coating was formed through the in-situ reaction of Al with the sprayed BN. The reaction was investigated by thermogravimetric-differential thermal analysis （TG-DTA）, and the phase composition in the synthetic process was characterized by X-ray diffraction （XRD）. Scanning electronic microscopy （SEM） was used to observe the morphology, and electron probe microanalysis （EPMA） was used to observe the distribution of the elements. The experimental results show that the AlN coating is dense and bonded with graphite tightly.展开更多
An experimental study on the heating of a mixture of aluminum and lithium hydroxide （LiOH） powders in a reductive bed under air atmosphere is reported. The formation of aluminum nitride （A1N） during this process w...An experimental study on the heating of a mixture of aluminum and lithium hydroxide （LiOH） powders in a reductive bed under air atmosphere is reported. The formation of aluminum nitride （A1N） during this process was the focus of this study. The formation of A1N was achieved using LiOH as an additive and heating the sample in a resistance furnace in a specially designed double crucible within a bed of a mixture of coke and filamentous calcium. The temperature range of the reaction was between 700℃ and 1100℃. The optimum temperature of 1100℃ and the optimum LiOH amount （Swt%） required to achieve maximum yield were determined by powder X-ray diffraction （XRD） analysis. Scanning electron microscopy （SEM） micrographs clearly indicated the transformation of grain structures from rods （700℃） to cauliflower shapes （1100℃）.展开更多
CrN powder was synthesized by nitriding Cr metal in ammonia gas flow, and its chemical reaction mechanism and nitridation process were studied. Through thermodynamic calculations, the Cr-N-O predominance diagrams were...CrN powder was synthesized by nitriding Cr metal in ammonia gas flow, and its chemical reaction mechanism and nitridation process were studied. Through thermodynamic calculations, the Cr-N-O predominance diagrams were constructed for different tempera- tures. Chromium nitride formed at 700-1200℃ under relatively higher nitrogen and lower oxygen partial pressures. Phases in the products were then investigated using X-ray diffraction （XRD）, and the Cr2N content varied with reaction temperature and holding time. The results indicate that the Cr metal powder nitridation process can be explained by a diffusion model. Further, Cr2N formed as an intermediate product because of an incomplete reaction, which was observed by high-resolution transmission electron microscopy （HRTEM）. After nitriding at 1000℃ for 20 h, CrN powder with an average grain size of 63 nm was obtained, and the obtained sample was analyzed by using a scanning electron microscope （SEM）.展开更多
Silicon nitride （Si3N4） powders were prepared by the direct nitridation of silicon powders diluted with a- Si3N4 at normal pressure. Silicon powders of 2.2 μm in average diameter were used as the raw materials. The...Silicon nitride （Si3N4） powders were prepared by the direct nitridation of silicon powders diluted with a- Si3N4 at normal pressure. Silicon powders of 2.2 μm in average diameter were used as the raw materials. The nitriding temperature was from 1623 to 1823 K, and the reaction time ranged from 0 to 20 min. The phase compositions and morphologies of the products were analyzed by X-ray diffraction and scanning electron microscopy, respectively. The effects of nitriding temperature and reaction time on the conversion rate of silicon were determined. Based on the shrinking core model as well as the relationship between the conversion rate of silicon and the reaction time at different temperatures, a simple model was derived to describe the reaction between silicon and nitrogen. The model revealed an asymptotic exponential trend of the silicon conversion rate with time. Three kinetic parameters of silicon nitridation at atmospheric pressure were calculated, including the pre-exponential factor （2.27 cm.s^-1） in the Arrhenius equation, activation energy （114 kJ·mol^-1）, and effective diffusion coefficient （6.2×10-s cm2.s^-1）. A formula was also derived to calculate the reaction rate constant.展开更多
基金Project(51725401) supported by the National Natural Science Foundation of China
文摘High purity vanadium nitride(VN)powders were prepared via a two-step process using vanadium trioxide(V2 O3)as the raw material.The V2 O3 was firstly reduced at 873 K in Ar atmosphere via magnesiothermic reduction reaction to get the mixture of V and MgO,and then the products were further nitrided at 1473 K in N2 atmosphere.Finally,the as-prepared samples were acid-leached to obtain pure VN powders.X-ray diffractometry and field-emission scanning electron microscopy were used to analyze the phase transition and morphological evolution of the samples.The results reveal that the overall morphology of the obtained VN powder retains the morphology of the initial V2 O3 powders.After removing MgO by acidic leaching,the porous VN particles can be obtained,with the oxygen content of 0.178 wt.%.Compared with the traditional methods,high purity VN powders with a small amount of oxygen and no carbon can be obtained.
基金financially supported by the National Natural Science Foundation of China(Nos.51772140 and 51862024)the Natural Science Foundation of Jiangxi Province(No.20171ACB21033)+1 种基金the Science and Technology Project of the Education Department of Jiangxi Province(No.GJJ170573)the Graduate Innovation Special Fund of Nanchang Hangkong University(No.YC2018-S358)。
文摘Sialon ceramics were prepared by the nitridation of Si,Al and Al2O3 powders with the transition metals(Fe Co,Ni)catalysts.The phase composition,microstructure and mechanical properties of specimens were studied Compared with the catalyst-free specimen,the addition of Fe,Co and Ni greatly promoted the nitridation process of Sialon ceramics and improved the weight gain rate and mechanical properties of specimens.With the increased content of catalysts,the apparent porosity of the products decreased first and then increased,contrary to flexural strength and compressive strength.The specimen with 2.5 wt%Fe had the highest flexural strength 145.8 MPa and it exhibited the highest compressive strength of 594.6 MPa when Co content was 2.5 wt%,whereas they were 71.9 and 78.7 MPa,respectively,when without catalyst.
基金Project(50274021) supported by the National Natural Science Foundation of China and Baoshan Iron and Steel Co., Ltd.
文摘β-Sialon/ZrN bonded corundum composites were synthesized using fused white corundum,alumina micro powder,zircon and carbon black by nitridation reaction sintering process. Phase composition and microstructure of the synthesized composites were investigated by X-ray powder diffraction and scanning electronic microscope,and the formation process of the composites was discussed. The results show that the composites with different compositions can be obtained by controlling the heating temperature and contents of zircon and carbon black. The proper temperature to synthesize the composites is 1773 K.
基金funded by the department of the Army Basic Research Program through the Edgewood Chemical and Biological Center,U.S.Army Research Office(No.W911NF-15-2-0052).
文摘Nanoparticles of refractory compounds represent a class of stable materials showing a great promise to support localized surface plasmon resonances(LSPRs)in both visible and near infrared(NIR)spectral regions.It is still challenging to rationally tune the LSPR band because of the difficulty to control the density of charge carriers in individual refractory nanoparticles and maintain the dispersity of nanoparticles in the processes of synthesis and applications.In this work,controlled chemical transformation of titanium dioxide(TiO_(2))nanoparticles encapsulated with mesoporous silica(SiO_(2))shells to titanium nitride(TiN)via nitridation reaction at elevated temperatures is developed to tune the density of free electrons in the resulting titanium-oxide-nitride(TiO_(x)N_(y))nanoparticles.Such tunability enables a flexibility to support LSPR-based optical absorption in the synthesized TiO_(x)N_(y)@SiO_(2) core-shell nanoparticles across both the visible and NIR regions.The silica shells play a crucial role in preventing the sintering of TiO_(x)N_(y) nanoparticles in the nitridation reaction and maintaining the stability of TiOxNy nanoparticles in applications.The LSPR-based broadband absorption of light in the TiO_(x)N_(y)@SiO_(2) nanoparticles exhibits strong photothermal effect with photo-to-thermal conversion efficiency as high as〜76%.
基金the New Century Excellent Youth Fund(NCET-04-0722)
文摘A novel method was used to fabricate AlN coating on graphite substrate. This approach included two steps： firstly, the emulsion composed of BN and anhydrous ethanol was sprayed on the surface of the graphite substrate; secondly, AlN coating was formed through the in-situ reaction of Al with the sprayed BN. The reaction was investigated by thermogravimetric-differential thermal analysis （TG-DTA）, and the phase composition in the synthetic process was characterized by X-ray diffraction （XRD）. Scanning electronic microscopy （SEM） was used to observe the morphology, and electron probe microanalysis （EPMA） was used to observe the distribution of the elements. The experimental results show that the AlN coating is dense and bonded with graphite tightly.
文摘An experimental study on the heating of a mixture of aluminum and lithium hydroxide （LiOH） powders in a reductive bed under air atmosphere is reported. The formation of aluminum nitride （A1N） during this process was the focus of this study. The formation of A1N was achieved using LiOH as an additive and heating the sample in a resistance furnace in a specially designed double crucible within a bed of a mixture of coke and filamentous calcium. The temperature range of the reaction was between 700℃ and 1100℃. The optimum temperature of 1100℃ and the optimum LiOH amount （Swt%） required to achieve maximum yield were determined by powder X-ray diffraction （XRD） analysis. Scanning electron microscopy （SEM） micrographs clearly indicated the transformation of grain structures from rods （700℃） to cauliflower shapes （1100℃）.
基金financially supported by the Innovation Foundation of Shanghai University (Nos. sdcx2012033 and sdcx2012062)the Special Research Foundation for Training and Selecting Outstanding Young Teachers of Universities in Shanghai (No. B.37-0407-12-008)+1 种基金the National Natural Science Foundation of China (Nos. 51072112 and 51272154)the Projects of International Cooperation and Exchanges NSFC (No. 51311130110)
文摘CrN powder was synthesized by nitriding Cr metal in ammonia gas flow, and its chemical reaction mechanism and nitridation process were studied. Through thermodynamic calculations, the Cr-N-O predominance diagrams were constructed for different tempera- tures. Chromium nitride formed at 700-1200℃ under relatively higher nitrogen and lower oxygen partial pressures. Phases in the products were then investigated using X-ray diffraction （XRD）, and the Cr2N content varied with reaction temperature and holding time. The results indicate that the Cr metal powder nitridation process can be explained by a diffusion model. Further, Cr2N formed as an intermediate product because of an incomplete reaction, which was observed by high-resolution transmission electron microscopy （HRTEM）. After nitriding at 1000℃ for 20 h, CrN powder with an average grain size of 63 nm was obtained, and the obtained sample was analyzed by using a scanning electron microscope （SEM）.
基金supported by the Natural Science Foundation of China(No.51106008)the Major State Basic Research and Development Program of China(No.2012CB720406)
文摘Silicon nitride （Si3N4） powders were prepared by the direct nitridation of silicon powders diluted with a- Si3N4 at normal pressure. Silicon powders of 2.2 μm in average diameter were used as the raw materials. The nitriding temperature was from 1623 to 1823 K, and the reaction time ranged from 0 to 20 min. The phase compositions and morphologies of the products were analyzed by X-ray diffraction and scanning electron microscopy, respectively. The effects of nitriding temperature and reaction time on the conversion rate of silicon were determined. Based on the shrinking core model as well as the relationship between the conversion rate of silicon and the reaction time at different temperatures, a simple model was derived to describe the reaction between silicon and nitrogen. The model revealed an asymptotic exponential trend of the silicon conversion rate with time. Three kinetic parameters of silicon nitridation at atmospheric pressure were calculated, including the pre-exponential factor （2.27 cm.s^-1） in the Arrhenius equation, activation energy （114 kJ·mol^-1）, and effective diffusion coefficient （6.2×10-s cm2.s^-1）. A formula was also derived to calculate the reaction rate constant.
