Preparation of Fine Metal Powders in Aqueous Process and Morphology Control

Metal powders were prepared by precursor—thermal decomposition method and chemical reduction method in aqueous solutions. In precursor—thermal decomposition method, the morphology and size of nickel powder were controlled via the thermal decomposition of nickel oxalate powder, that was prepared by mixing a solution containing oxalic acid ion with some kinds of nickel sources such as nickel ion, ammoniacal nickel complex ion, and nickel hydroxide. Needle-like nickel oxalate powder with high aspect ratio, [Ni(NH3)2]C2O4 2H2O, was synthesized by using ammoniacal nickel complex ion, and rectangular parallelepiped shape of nickel oxalate powder, NiC2O4 2H2O, was by nickel hydroxide. As for the chemical reduction method in aqueous solution, ascorbic acid (vitamin C) at pH 3 reacts with copper ion as a reducing agent, and copper metal particle in size of 100 nm was obtained. Under the condition of pH > 3, reduction property is weakened, and precipitates consisted of copper powder with cuprous oxide. Ti3+ ion (Ti2(SO4)3 solution) also has a reducing property for copper ion and acts as a new reducing agent in liquid phase reduction process.