The oxidation of oxygen ions and the generation of an anode effect at a low oxygen content of 150 mg/kg were discussed in this paper.Cyclic voltammetry and square-wave voltammetry tests were conducted to explore the a...The oxidation of oxygen ions and the generation of an anode effect at a low oxygen content of 150 mg/kg were discussed in this paper.Cyclic voltammetry and square-wave voltammetry tests were conducted to explore the anodic processes of LiF-NdF_(3)melt after a lengthy period of pre-electrolysis purification at 1000℃(during which the oxygen content reduced from 413 to 150 mg/kg).The oxidation process of oxygen ions was found to have two stages:oxidation product adsorption and CO/CO_(2)gas evolution.The adsorption stage was controlled by diffusion,whereas the gas evolution was controlled by the electrochemical reaction.In comparison with oxygen content of 413 mg/kg,the decrease in the amplitude of the current at low oxygen content of 150 mg/kg was much gentler during the forward scanning process when the anode effect occurred.Fluorine-ion oxidation peaks that occurred at about 4.2 V vs.Li/Li+could be clearly observed in the reverse scanning processes,in which fluorine ions were oxidized and perfluorocarbons were produced,which resulted in an anode effect.展开更多
In this study,ultrafine HfB_(2) powders with low oxygen were synthesized by a flocculating settling process which yielded ceramic precursors and subsequent carbo/borothermal reduction of the precursors.The liquid phas...In this study,ultrafine HfB_(2) powders with low oxygen were synthesized by a flocculating settling process which yielded ceramic precursors and subsequent carbo/borothermal reduction of the precursors.The liquid phase precursor method can achieve uniform mixing of components at the molecular level through multiple complexation reactions,and then realize the carbo/borothermal reduction reaction at a lower temperature to obtain ultrapure HfB2 powders.The as-resulted quasi-spherical HfB2 powders under the optimum conditions(atomic molar ratio M:B:C=1:2.8:10)calcined at 1500°C for 1 h have an average particle size of 205 nm and an oxygen content of 0.097 wt.%.Detailed analysis of the phase evolution of precursors shows that the formation of HfB2 particles is a mass diffusion mode from the external to internal HfO_(2)cores.We reveal that below 1300°C,HfC is not an intermediate product of HfB2 powder during the transition of precursors.Instead,HfC was formed as a by-product at high temperatures in the carbo/borothermal reduction process.The proposed formation mechanism of HfB_(2) is completely different from the traditional two-step transformation method.After the sintering of the ultrafine powders,the HfB_(2) ceramics show a relative density of 96.1%and superior mechanical properties compared to other works.Furthermore,by simply replacing the initial metal source,chlorinated group IV and V transitional metals(Ti,Zr,Ta,Nb)can also convert into high-purity and ultrafine diborides.This work shows that flocculating settling assisted carbo/borothermal reduction has potential in lot size production of various high-purity and ultrafine boride powders.展开更多
基金the National Natural Science Foundation of China(No.51774145).The“Minjiang Scholar”Program of Department of Education,Fujian Province,China was also acknowledged.
文摘The oxidation of oxygen ions and the generation of an anode effect at a low oxygen content of 150 mg/kg were discussed in this paper.Cyclic voltammetry and square-wave voltammetry tests were conducted to explore the anodic processes of LiF-NdF_(3)melt after a lengthy period of pre-electrolysis purification at 1000℃(during which the oxygen content reduced from 413 to 150 mg/kg).The oxidation process of oxygen ions was found to have two stages:oxidation product adsorption and CO/CO_(2)gas evolution.The adsorption stage was controlled by diffusion,whereas the gas evolution was controlled by the electrochemical reaction.In comparison with oxygen content of 413 mg/kg,the decrease in the amplitude of the current at low oxygen content of 150 mg/kg was much gentler during the forward scanning process when the anode effect occurred.Fluorine-ion oxidation peaks that occurred at about 4.2 V vs.Li/Li+could be clearly observed in the reverse scanning processes,in which fluorine ions were oxidized and perfluorocarbons were produced,which resulted in an anode effect.
基金financially supported by the National Science Fund for Distinguished Young Scholars(No.51825103)the National Science Fund for Excellent Young Scholars(No.52222208)+1 种基金the Major science and technology project of Anhui Province(No.008192841048)the HFIPS Director's Fund,CAS(No.BJPY2021B04,YZJJ202202-CX,YZJJKX202202).
文摘In this study,ultrafine HfB_(2) powders with low oxygen were synthesized by a flocculating settling process which yielded ceramic precursors and subsequent carbo/borothermal reduction of the precursors.The liquid phase precursor method can achieve uniform mixing of components at the molecular level through multiple complexation reactions,and then realize the carbo/borothermal reduction reaction at a lower temperature to obtain ultrapure HfB2 powders.The as-resulted quasi-spherical HfB2 powders under the optimum conditions(atomic molar ratio M:B:C=1:2.8:10)calcined at 1500°C for 1 h have an average particle size of 205 nm and an oxygen content of 0.097 wt.%.Detailed analysis of the phase evolution of precursors shows that the formation of HfB2 particles is a mass diffusion mode from the external to internal HfO_(2)cores.We reveal that below 1300°C,HfC is not an intermediate product of HfB2 powder during the transition of precursors.Instead,HfC was formed as a by-product at high temperatures in the carbo/borothermal reduction process.The proposed formation mechanism of HfB_(2) is completely different from the traditional two-step transformation method.After the sintering of the ultrafine powders,the HfB_(2) ceramics show a relative density of 96.1%and superior mechanical properties compared to other works.Furthermore,by simply replacing the initial metal source,chlorinated group IV and V transitional metals(Ti,Zr,Ta,Nb)can also convert into high-purity and ultrafine diborides.This work shows that flocculating settling assisted carbo/borothermal reduction has potential in lot size production of various high-purity and ultrafine boride powders.
