The roles of ammonia and ammonium bicarbonate in the preparation of nickel particles from nickel chloride

The roles of NH₃· H₂O and NH₄HCO₃in the preparation of Ni particles from NiCl₂· 6H₂O aqueous solution by ultrasonic spray pyrolysis were investigated. The results showed that both ammonia and ammonium bicarbonate had a remarkable influence on the solution chemistry and the resulting particles, and could significantly modify the reaction pathway. After the addition of these additives to the precursor solution, intermediate NiO was formed initially, followed by reduction to metallic Ni in the presence of a reductive gas. H₂is a powerful reducing agent; however, metallic Ni could also be obtained in the absence of H₂in the carrier gas. In the latter case, it was shown that NH3 was primarily responsible for Ni formation. A description of the mechanisms and processes of Ni formation during spray pyrolysis is proposed.