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

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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.