The corrosion behaviour of nickel in molten NaNO3KNO3 eutectic

Abstract

The corrosion (oxidation) of nickel in molten (Na, K)NO₃ eutectic has been investigated at temperatures ranging from 250 °C to 450 °C, for exposure periods of up to 12 h. The results of both weight-gain and potential measurements under open-circuit conditions reveal the formation of a passivating film consisting mainly of NiO. The thickening of the oxide film proceeds according to a parabolic law, at a rate depending on the temperature of the melt. The activation energy of the process was estimated to be 14.95 kcal mol⁻¹, indicating that the oxidation process of nickel is determined by diffusion of nickel in the form of ions and electrons via vacancies and holes. A break was observed in the parabolic plots at higher temperatures; this may indicate a change in the mechanism of film growth. The results are discussed in terms of oxidation kinetics data for nickel in both molten nitrates and air at high temperatures.