A novel electro-aluminothermic route to V-Ni alloys: Ca₃(VO₄)₂ as the vanadium source

Ca₃(VO₄)₂ enables stable electro-aluminothermic production of V-rich V-Ni alloys through in situ CaO-Al₂O₃ slag formation that promotes metal-slag separation, while immediate furnace cooling suppresses impurity and inclusion formation. To develop a scalable route, we evaluated NaVO₃, NH₄VO₃, and Ca₃(VO₄)₂ as vanadate precursors for thermite reduction-alloying. NaVO₃ forms a Na₂O-rich slag that is low-melting and highly hygroscopic, requiring additional flux and aggravating spattering and slag discharge. Direct reduction of untreated NH₄VO₃ releases NH₃ and H₂O, which suppresses the self-propagating reaction and leads to the incorporation of N and H into the alloy. These issues markedly narrow the operating window, whereas Ca₃(VO₄)₂ can react smoothly to yield well-separated alloy and slag phases. Therefore, Ca₃(VO₄)₂ was selected for further investigation, and the formation of V-Ni alloys and the evolution of impurities were studied in the Ca₃(VO₄)₂-Al-Ni electro-aluminothermic system. CaO generated combines with Al₂O₃ to form a stable CaO-Al₂O₃ slag layer, which buffers the exothermic reaction, suppresses spattering, and eliminates the need for external slag formers. Extending the post-reaction holding time from 0 to 15-30 min does not decrease impurity levels; instead, the contents of O, Al, C, and N increase, accompanied by the formation of more ellipsoidal Al₂O₃-type inclusions. Immediate furnace shutdown followed by furnace cooling, while minimizing contact with external media, effectively suppresses impurity incorporation and inclusion formation. This work demonstrates a Ca₃(VO₄)₂-enabled route for preparing V-rich V-Ni alloys and provides a mechanistic basis for process control in vanadate-derived alloy production.