Preparation of pure nickel, cobalt, nickel–cobalt and nickel–copper alloys by hydrothermal reduction

Abstract

Reduction of aqueous NiSO ₄ , CoSO ₄ and CuSO ₄ with hydrazine has been investigated systematically to obtain ultrafine powders of pure nickel and cobalt, and of nickel–cobalt and nickel–copper alloys. The results show that the pH value and the temperature are the key factors to influence the reactions. When pH ≥ 10.0 and the temperature is higher than 85 °C, pure nickel particles are obtained. Pure cobalt, and nickel–cobalt and nickel–copper alloy powders can be formed only when pH ≥ 13 and the temperature is above 120 °C. The mechanism for the formation of powders of nickel and cobalt, and of nickel–cobalt and nickel–copper alloys is discussed. The XRD patterns reveal that the as-synthesized pure cobalt is the hexagonal phase (h.c.p.), the pure nickel is the cubic phase (f.c.c.) and the Co _1–x Ni _x and Cu _1–x Ni _x alloys are the f.c.c. phase only when the ratio of Ni to Co is above 1∶1 and Ni∶Cu is below 1∶9, respectively.