瞬时离子释放扩散模型及熔盐电解固态WS_2制备纳米W的液相扩散研究

固态化合物熔盐电解冶金在21世纪初被提出后受到学术界和工业界的广泛关注.根据固态化合物电解的动态三相电化学界线模型,固态金属氧(硫)化物阴极在电解还原过程中,涉及O2?(S2?)在电解生成的多孔金属层中的液相扩散,但由于一直以来缺乏方便可靠的理论和实验方法,相关传质过程动力学的研究鲜有文献报道.本文引入多孔电极瞬时离子释放扩散模型,以粉末微腔电极为微型多孔电极,设计双电势阶跃实验研究了WS2在等摩尔比NaCl+KCl熔盐中电解时固态阴极中的液相扩散.实验结果与理论模型符合良好,973 K时,硫离子在孔隙率为69%的多孔金属钨层中的扩散系数为0.92×10?5 cm2/s,扩散活化能为53.4 kJ/mol.研究表明,二硫化钨在NaCl+KCl混盐体系中能够快速电解还原生成纳米金属钨,其中,S2?的扩散传质是整个电解过程的速度控制步骤.

Study of liquid ion diffusion in electroreduction of solid WS2 cathode to nanometer W in molten NaCI-KCI using an instantaneous ion release and diffusion model

Over the past few years, preparation of metals by molten salt electrolysis of solid metal oxide （or sulfide） cathodes has attracted numerous interests from both academic and industrial communities. According to the three-phase interlines theories, diffusion of O2- （or S2-） ions should play an important role in the solid cathode process, however, it has seldom been studied due to the absence of both convenient theoretical and experimental methods. In this work, we introduced an instantaneous ion release diffusion model （IIRD Model） for porous electrodes as theoretical base, and fabricated mini porous electrodes by filling WS2/W mixture into the cylindrical cavities in a Mo foil substrate and performed double potential operations to study the liquid diffusion of S2- ions in the solid sulfide cathode in the equi-molar NaC1-KC1 melts. The experimental results were in good accord with the theoretical equation. By curve fitting, the diffusion coefficient of S2- ions in the electrolysis generated porous W layer was evaluated as 9.2×10-6 cm2/s at 973 K, with the diffusion activation energy of about 53.4 kJ/mol. The study indicates that electrochemical reduction of WS2 to nanometer W can be achieved very quickly, and the electrolysis of solid WS2 cathode should be rate determined by the liquid diffusion of Seions in the generated porous W layer.