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Molten salt electrolysis is an economical and green method in metal extraction and refining, which plays an important role in energy saving and emissions reducing. In recent years, the research on molten salt electrolysis mainly focuses on exploring the electrochemical behavior of ions on the cathode and its related thermodynamics, while the research on the kinetic process of ions is less and lacks a more systematic theoretical system. Therefore, this paper aims to review the kinetic processes and influencing factors related to the reaction on different cathodes in the molten salt electrolysis process. According to the differences in cathodic reactions and electrode states, a systematic review was conducted on the formation and diffusion process of multiphase interfaces in cathodes. Overall, this work is beneficial for promoting the development of strategies for enhancing the kinetics of multiple cathodic reaction, morphological control of electrolytic products and so on. [Display omitted] • The kinetic process of ions on cathode in molten salt electrolysis was studied systematically. • Discussed the different types and process mechanisms of atom diffusion on the cathode surface and inside. • Clarified the fundamental elements of cathodic kinetic processes. • Conducive to effectively regulate the cathodic reaction process according to subjective initiative. [ABSTRACT FROM AUTHOR]

Abstract The reduction of metal oxides by hydrogen is a very significant reaction in metallurgical industries. Particularly, hydrogen reduction is one of the effective methods to reduce CO 2 emission in iron and steel industry. The mathematical modeling of H 2 reduction process would help to define the operating parameters and to get a better control of the reduction process. In this study, a new kinetic model regarding hydrogen reduction of metal oxides controlled by external gas diffusion has been proposed. The model has incorporated numbers of parameters such as temperature, size of the metal oxides, diffusion coefficient constant, hydrogen partial pressure, density of metal oxides and time. Furthermore, the shape of metal oxides (spherical, cylindrical, lamellar particles) was considered as well, and the models for the reduction of metal oxides with different shapes were combined to a formula. Also, the developed model can be applied to describe the reduction kinetics under both isothermal and non-isothermal conditions. Because the model is in the analytic function, therefore, it is convenient for usage and theoretical analysis. Application of the developed model to practical systems validated that its predicted values agreed very well with the experimental data. Highlights • Kinetic model for the external gas diffusion controlling reduction was proposed. • The model is in the analytic function and is convenient for theoretical analysis. • The shape of metal oxides was considered. • The models for different shapes were combined to a formula. [ABSTRACT FROM AUTHOR]

In the present study, a new and simple method to prepare tungsten and tungsten carbides powders was proposed by using WO 3 powders as the raw material and CH 3 OH vapor as the reduction and carbonization agent. Both thermodynamic and experimental studies were carried out, and based on the results, the reaction routes were obtained. It was found that at low and moderate temperatures, the final product of WC was formed via intermediates of W 18 O 49 , WO 2 , partial metallic W and W 2 C; while at high temperature, WO 3 was first reduced to WO 2 with the intermediate phase of W 18 O 49 , and then reduced to W. The morphology of final products almost retained the same shape as that of raw materials WO 3 at low temperature, however, the large particles with blocky shape disappeared and the products were all small W particles with polyhedral shape at high temperature. Furthermore, the reaction mechanisms were proposed: the pseudomorphic transformation mechanism dominated the reaction at low temperature, but at high temperature, the reduction obeyed the chemical vapor transport mechanism, which is beneficial for grain refining of final product. [ABSTRACT FROM AUTHOR]

Tungsten carbides, which can be widely used as cutting and drilling tools, chemical catalysts and aerospace coatings, have attracted widespread attentions. The present work reported a simple method to prepare tungsten carbides by using WO 2 as the raw materials and CO as the reduction and carbonization agent. It was found that at lower and moderate temperatures, all the final product was WC, while at higher temperatures, the final products were W 2 C or W. The reduction and carbonization mechanism was also studied theoretically and experimentally. WO 2 was reduced and carburized to WC in one step at lower temperatures; WO 2 was first reduced and carburized to W 2 C and then to WC at moderate temperatures; while at higher temperatures, WO 2 was first reduced to metallic W and then carbonized to WC or W 2 C, but with the temperature increasing, the carbonization became difficult and required much higher CO content. [ABSTRACT FROM AUTHOR]