Optimization, Kinetic and thermodynamic studies of MiLd steel corrosion in different soils

Abstract

Response Surface Methodology (RSM) based on the central composite rotatable design was used to determine the optimum conditions for the corrosion rate of mild steel in three different soils viz; Clay, Loamy and Sandy soils. The parameters Time (1-3 hours) and Temperature (303-313K) were assessed as controlling factors for the investigation of corrosion rate of mild steel in the different soils. The result shows the optimum corrosion rate of 54, 48 and 40 gm-2day-1 for Clay, Loamy and Sandy soils respectively obtained at time 2.5hr and temperature of 387.5K. A quadratic equation was obtained by multiple regression analysis for predicting the optimisation of the corrosion rate of mild steel in the different soils. This study also investigated the effect of temperature within the range of 298-383K on the corrosion rates on mild steel in Clay, Loamy and Sandy soils using weight loss method. It was observed that as temperature increases the corrosion rate also increases. The kinetic functions in terms of the pre-exponential factor, (A) was found to be 247.3984, 295.0073 and 171.0575 and the activation energy (Ea) 5.2045, 6.1856, 5.4623 for clay, loamy and sandy soil respectively. A high activation energy and low pre-exponential factor implies a low corrosion rate hence sandy soil showed minimum corrosion rate. The thermodynamic function in terms of ∆H, ∆S, and ∆G were studied using the Arrhenius and Transition state equations respectively. The result showed that the corrosion process in the soils is endothermic and the reaction is spontaneous at 298, 323 and 383K.