Kinetics of the Plasma–Solution Synthesis of Nickel Oxide

The kinetics of formation of insoluble nickel hydroxy compounds initiated by the exposure of Ni(NO3)2·6H2O aqueous solutions to an atmospheric-pressure direct current discharge in air has been studied. It has been found that these compounds are formed as colloidal systems only if the solution acts as a discharge anode. No colloidal solutions are formed if the solution acts as a cathode. The studied solution concentration range is 20–60 mmol/L, and the discharge currents are 20–60 mA. It has been found that the kinetics of decrease in the Ni2+ ion concentration depends on the concentration (zero/first kinetic order of the reaction) and does not depend on discharge current. The rate constants and rates of decrease in the Ni2+ ion concentration, ion conversion, and the energy efficiency of the ion conversion process have been determined. The conversion and energy efficiency depend on the discharge current and initial concentration and are 4–25% and 0.1–0.5 ions per 100 eV, respectively. X-ray diffraction studies have shown that the resulting precipitates are represented by a Ni(OH)2 powder; the calcination of the powder leads to the formation of crystalline β-NiO.