Preparation of fine Ni powders from nickel hydrazine complex

Fine nickel powders with narrow size distribution have been prepared from the reduction of nickel hydrazine complexes in aqueous solution. The pure nickel hydrazine complexes, [Ni(N₂H₄)₃]Cl₂ were prepared with the molar ratio of N₂H₄/Ni²⁺ = 4.5, while a mixture of complexes, such as Ni(N₂H₄)₂Cl₂, [Ni(N₂H₄)₃]Cl₂, and [Ni(NH₃)₆]Cl₂ were formed with N₂H₄/Ni²⁺ < 4.5. By the X-ray diffraction (XRD), FT-IR, and scanning electron microscopy (SEM) analyses, it was found that the reduction of Ni²⁺ to metallic Ni powder proceeded via the formation of nickel hydroxide which was reduced by hydrazine liberated from the ligand exchange reaction between the nickel hydrazine complex and NaOH. The standard deviation of the particle size decreased with the decreasing molar concentration of nickel hydrazine complex while the mean particle size increased. As the amount of hydrazine increased, the surface roughness of the particles was improved significantly due to the catalytic decomposition of the excess hydrazine at the surface of the nickel particle. It was found that average particle size could be controlled from 150 to 380 nm by adjusting the reaction molar ratio and temperature.