Nickel particles prepared from nickel nitrate with and without urea by spray pyrolysis

Nickel particles were prepared by spray pyrolysis of 0.5 M Ni(NO3)2·6H2O solution with hydrogen at a residence time of 19 s. All the product particles were composed of nickel oxide and nickel with no trace of nickel nitrate under the condition. The particles were completely reduced to nickel at a furnace set temperature of 410 °C. However, it was not until 850 °C that the spherical particles fully densified and crystallized appeared. Use of urea enhanced the solidness and surface smoothness of the particles, while slightly reducing the rate of metallization. The urea enabled to prepare the nickel particles even without hydrogen though under stricter conditions. The rates of metallization and sintering/crystallization were slightly affected by the residence time and initial salt concentration. Higher crystallized nickel particles had higher resistance to oxidation in air environment.