Accelerated molten salt electro-deoxidation for ultrafine tantalum powder synthesis via intermediate microstructural modulation

Abstract

The molten salt electro-deoxidation, i.e. the FFC (Fray-Farthing-Chen) process, demonstrates considerable potential for the synthesis of tantalum powder. However, its practical application is hindered by the long electrolysis duration. This study proposes an accelerated electro-deoxidation process in molten Na₃AlF₆-AlF₃ salts for preparing ultrafine Ta powder, which achieves a sequential cathode phase transformation from Ta₂O₅ through intermediate NaTaO₃ to Ta. NaTaO₃ is formed through in situ interfacial reactions between Ta₂O₅ and the electrolyte. We demonstrate for the first time that the growth of the FFC-type intermediate is driven by nanoparticle assembly and oriented attachment mechanism. This growth mechanism is influenced by the structure of the electrolyte/particle interface. By constructing a novel hierarchical pore structure Ta₂O₅ cathode with optimized interfaces, we facilitated a microstructurally controllable transformation of Ta₂O₅ to fine NaTaO₃, thereby effectively mitigating the elongation of oxygen ions solid diffusion pathway induced by intermediate coarsening. In the case of self-assembled NaTaO₃, the weak bonding between the nanoparticles also favors the kinetics of their subsequent decomposition into Ta. This approach has been shown to enable the complete reduction of 1 g of Ta₂O₅ within only 1 h, demonstrating a significant enhancement in process efficiency. The resulting Ta powder exhibits uniform monodisperse morphology and good capacitive behavior in Na₂SO₄ electrolyte solution. The present study may now guide the way towards establishing the electrochemical route for the efficient preparation of many other refractory powders materials.