Kinetics of dissolution of nichrome in hydrochloric acid

Abstract

Nichrome is extensively used in heating elements in industrial furnaces and metallurgical industries. In this investigation, studies were carried out to determine the dissolution characteristics of nichrome in hydrochloric acid, with or without their respective salts, at various concentrations. Nickel and chromium in dissolved nichrome solution were analysed using atomic absorption spectrophotometry. The dissolution studies were conducted at different concentrations of hydrochloric acid, ranging from 0.5 to 6.0 M and also in mixtures of hydrochloric acid and sodium chloride (1.0–3.5 M), keeping the HCl concentration constant at 1.0 M. The effect of temperature (40–100°C) on the dissolution of nichrome in 6.0 M HCl for different periods is also reported. The activation energy was found to be 58.6 kJ/mol. The results of the kinetic study have been used to elucidate the mechanism of the process by applying Langmuir's adsorption isotherm. The experimental results confirm the mechanism that both hydrogen and chloride ions are responsible for the dissolution process. In simple hydrochloric acid, the hydrogen ion is rate controlling, whereas in mixtures of hydrochloric acid and excess amounts of sodium chloride, the chloride ion is responsible for determining the rate of dissolution. In low concentrations of hydrochloric acid (0.04–0.22 M) and high concentrations of sodium chloride (1.0–4.0 M) the observed constancy in the rate of reaction has been attributed to saturation of the active sites of the nichrome surface by the chloride ion.