Effect of Ammonia on the Crystal Morphology of Nickel Oxalate Precipitates and their Thermal Decomposition into Metallic Nickel

Abstract

Morphology- and size-controlled nickel powder was synthesized via the thermal decomposition of nickel oxalate, which was prepared by mixing a solution containing nickel chloride hexahydrate (NiCl2� 6H2O) and aqueous ammonia (NH3� H2O) with a solution of sodium oxalate (Na2C2O4) under controlled conditions. Nickel precursors ca. 1 mm long and 0.05 mm wide were obtained using 1.2 mol dm � 3 aqueous ammonia and 0.2 mol dm � 3 nickel chloride hexahydrate, pH 9.5, and 293 K. The morphology of the precursor changed from granular to needle-like with increasing aqueous ammonia concentration. Large dispersed needle-like particles were obtained at 353 K. Nickel metal powder was obtained that was needle-like or filament in shape depending on the heat treatment temperature of the needle-like nickel precursor.