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

Reduction of aqueous NiSO4, CoSO4 and CuSO4 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 greater than or equal to 10.0 and the temperature is higher than 85 degrees C, pure nickel particles are obtained. Pure cobalt, and nickel-cobalt and nickel-copper alloy powders can be formed only when pH greater than or equal to 13 and the temperature is above 120 degrees 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 Co1-xNix and Cu1-xNix 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.