Hydrothermal Synthesis and Structural Characteristics of Nickel−Platinum Bimetallic Powders

The co-reduction of platinum and nickel complex compounds with hydrazine hydrate in alkaline aqueous ammonia solutions was studied under hydrothermal autoclave conditions. It was established that quantitative precipitation of nickel and platinum occurred within 1 h at a temperature of 110°C. All phases formed upon the reduction had fcc lattices and ferromagnetic behavior. The formation of nickel−platinum substitutional solid solutions was proved by powder X-ray diffraction. The nickel to platinum molar ratio was varied from 16 : 1 to 0.5 : 1, and in all cases, two phases of the nickel−platinum substitutional solid solution were detected, namely, a phase of variable composition depending on the initial molar ratio of nickel and platinum with a lattice parameter of 3.622−3.772 Å, which corresponds to 25–62 at % platinum, and a platinum-enriched phase (90–95 at %) with almost invariable composition and a lattice parameter of 3.885–3.901 Å. For molar ratios from 16 : 1 to 1 : 1, in addition to two solid solution phases, a nickel metal phase with a crystal lattice parameter of 3.527 Å was clearly seen. When the initial ratio of nickel to platinum was 0.5 : 1, no nickel metal phase was found. Under hydrothermal conditions, nickel dissolved in 1 M hydrochloric acid, while solid solutions were chemically and structurally stable.