One-step synthesis of spherical Al3Ta alloy powder by electrolyzing solid Ta2O5 in molten fluorides

Abstract

Aluminum-tantalum powders are emerging as new raw materials for additive manufacturing (AM) technologies, but their preparation in bulk quantities and in powder form via conventional metallurgical methods is challenging. In this study, we report a one-step synthesis of spherical Al₃Ta powder by direct electrolyzing solid Ta₂O₅ cathode (vs. a graphite anode) in molten Na₃AlF₆-K₃AlF₆-AlF₃-LiF-Al₂O₃. Cyclic voltammetry and constant potential electrolysis techniques were employed to characterize the electrochemical reaction process, along with X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) for the structural and morphological analyses. The process involves an initial Ta₂O₅ electro-deoxygenation process, the subsequent electrodeposition of Al³⁺ on the formed Ta particles and an in-situ alloying process. The innovative use of Ta₂O₅ cathodes with a novel hierarchical porous structure allows for a controlled transformation of cathode particle morphology and facilitates the rapid generation of nanoscale tantalum particles. Al³⁺ from the electrolyte is then electrodeposited onto these particles, initiating an in-situ alloying reaction. This is an exothermic process that facilitates the diffusion of aluminum atoms into tantalum, and reduces the interfacial energy promoting the formation of spherical Al₃Ta particles. Such powders are in demand for AM techniques. The findings may now guide the way to establishing the electrochemical route for the short-process preparation of other high-temperature alloy powders.