Kinetic and mathematical approaches to the corrosion of mild steel in nitric acid

Abstract

The effect of different temperatures and acid concentrations on the corrosion of mild steel in nitric acid are addressed in this work. The effect of temperature is explained by the application of the Arrhenius equation and transition state theory, while the acid concentration effect is explained using reaction kinetic equations. The combined effect of temperature and acid concentration is then modeled using a nonlinear regression method. Thermodynamic parameters of activation (E, ΔH* and ΔS*) and detailed kinetic studies for the corrosion reaction are carried out. Nonlinear corrosion rates as a function of temperature and acid concentration are estimated with a good prediction of corrosion rate values. The values of activation energy E and enthalpy of activation ΔH* decrease with an increase in acid concentration indicating the increasing reaction rate. Entropies of activation ΔS* tend to lower values with increasing acid concentration, which indicates that the activated complex is more orderly relative to the initial state. The corrosion reaction was approximately first order.