The cathodic reduction mechanism of Hf(Ⅳ)ions in a fused Na Cl–KCl–Na F–K_(2) HfF_(6) salt system was studied in various Na F concentrations at 1073 K to obtain a purified dendritic Hf metal.The results of cyclic ...The cathodic reduction mechanism of Hf(Ⅳ)ions in a fused Na Cl–KCl–Na F–K_(2) HfF_(6) salt system was studied in various Na F concentrations at 1073 K to obtain a purified dendritic Hf metal.The results of cyclic voltammetry and square wave voltammetry indicated that the reduction process comprised two steps of Hf(Ⅳ)→Hf(Ⅱ)and Hf(Ⅱ)→Hf at low Na F concentrations(0<molar ratio of[F-/Hf 4+]≤17.39)and one step of Hf(Ⅳ)→Hf at high Na F concentrations(17.39<molar ratio of[F-/Hf 4+]<23.27).The structure and morphology of the deposits obtained in potentiostatic electrolysis in the one-step reduction process were analyzed and verified by X-ray diffraction,scanning electron microscopy,and energy dispersive X-ray spectrometry.In the one-step reduction process,the disproportionation reaction between the Hf metal and Hf complex ions was inhibited,and a large dendrite Hf metal was achieved in molten salt electrorefining.展开更多
The electrochemical reduction mechanism of hafnium ion（IV） was studied in NaC1-KC1-K2HfC16 melts on a molybdenum electrode. The cyclic voltammetry study shows that Hf（IV） is reduced to hafnium metal in double two-...The electrochemical reduction mechanism of hafnium ion（IV） was studied in NaC1-KC1-K2HfC16 melts on a molybdenum electrode. The cyclic voltammetry study shows that Hf（IV） is reduced to hafnium metal in double two-electron process, that is： Hf（IV） ＋ 2e→Hf（II） and Hf（II） ＋ 2e- →Hf, and the electrochemical reduction of Hf（IV） pro- cess was diffusion-controlled. The diffusion coefficients were calculated at several temperatures, and the results obey the Arrhenius law. According to the relationship oflnD versus 1/T, the corresponding activation energy was determined to be 158.8 kJ.mol- x. The square wave voltammetry results further confirm the reduction mechanism of hafnium.展开更多
In this article, we put forward a new approach to estimate multiple conditional regression quantiles simultaneously. Unlike the double summation method in most of the literatures, our proposed model allows continuous ...In this article, we put forward a new approach to estimate multiple conditional regression quantiles simultaneously. Unlike the double summation method in most of the literatures, our proposed model allows continuous variety for the quantile level over(0,1). As a result, all the quantile curves can be obtained via a 2-dimensional surface simultaneously. Most importantly, the proposed minimizing criterion can be readily transformed to a linear programming problem. We use tensor product bi-linear quantile smoothing B-splines tofit it. The asymptotic property of the estimator is derived and a real data set is analyzed to demonstrate the proposed method.展开更多
基金the National Natural Science Foundation of China(No.51204021)。
文摘The cathodic reduction mechanism of Hf(Ⅳ)ions in a fused Na Cl–KCl–Na F–K_(2) HfF_(6) salt system was studied in various Na F concentrations at 1073 K to obtain a purified dendritic Hf metal.The results of cyclic voltammetry and square wave voltammetry indicated that the reduction process comprised two steps of Hf(Ⅳ)→Hf(Ⅱ)and Hf(Ⅱ)→Hf at low Na F concentrations(0<molar ratio of[F-/Hf 4+]≤17.39)and one step of Hf(Ⅳ)→Hf at high Na F concentrations(17.39<molar ratio of[F-/Hf 4+]<23.27).The structure and morphology of the deposits obtained in potentiostatic electrolysis in the one-step reduction process were analyzed and verified by X-ray diffraction,scanning electron microscopy,and energy dispersive X-ray spectrometry.In the one-step reduction process,the disproportionation reaction between the Hf metal and Hf complex ions was inhibited,and a large dendrite Hf metal was achieved in molten salt electrorefining.
基金financially supported by the National Natural Science Foundation of China(No.51204021)the National Science and Technology Plan of China(No.2012BAB10B10)
文摘The electrochemical reduction mechanism of hafnium ion（IV） was studied in NaC1-KC1-K2HfC16 melts on a molybdenum electrode. The cyclic voltammetry study shows that Hf（IV） is reduced to hafnium metal in double two-electron process, that is： Hf（IV） ＋ 2e→Hf（II） and Hf（II） ＋ 2e- →Hf, and the electrochemical reduction of Hf（IV） pro- cess was diffusion-controlled. The diffusion coefficients were calculated at several temperatures, and the results obey the Arrhenius law. According to the relationship oflnD versus 1/T, the corresponding activation energy was determined to be 158.8 kJ.mol- x. The square wave voltammetry results further confirm the reduction mechanism of hafnium.
基金partially supported by the National Natural Science Foundation of China(No.11861042)the Fundamental Research Funds for the Central Universitiesthe Research Funds of Renmin University of China(No.18XNL012)。
文摘In this article, we put forward a new approach to estimate multiple conditional regression quantiles simultaneously. Unlike the double summation method in most of the literatures, our proposed model allows continuous variety for the quantile level over(0,1). As a result, all the quantile curves can be obtained via a 2-dimensional surface simultaneously. Most importantly, the proposed minimizing criterion can be readily transformed to a linear programming problem. We use tensor product bi-linear quantile smoothing B-splines tofit it. The asymptotic property of the estimator is derived and a real data set is analyzed to demonstrate the proposed method.
