Structural and morphological transformations during NiO and Ni particles generation from chloride precursor by ultrasonic spray pyrolysis

Abstract

Submicrometer NiO and Ni powders were obtained by ultrasonic spray pyrolysis of aqueous solutions of NiCl 2 followed by thermal decomposition of generated aerosols in an oxidation or N 2 H 2 reduction atmosphere, respectively. Particle sizes of the prepared powders can be controlled by the change of reaction temperature and the concentration of initial solutions. Pyrolysis temperatures in the range from 973 to 1273 K, non-agglomerated ideally spherical NiO and relatively spherical Ni particles with a mean diameter of 0.5–0.8 μm were obtained. Generation of NiO particles proceeds gradually from NiCl 2 · 6H 2O dehydration and NiCl 2 oxidation to NiO formation. Ideal spheres of NiO particles were prepared due to sufficient residence time of droplets in the drying and pyrolysis process and due to the conditions needed for the volume precipitation. The process of nickel formation proceeds through all previous transformations followed by the reduction of NiO into nickel. Insufficient residence time of droplets in the case of nickel preparation is the cause of incomplete spheroidization of particles.