KINETICS AND THERMODYNAMICS STUDIES OF CORROSION OF ZINC IN MIXED SOLVENTS

Abstract

The first chapter presents an introductory remarks on corrosion processes such as types, factors affecting the rate of corrosion, corrosion protection, corrosion of zinc metal and literatures survay of corrosion behaviour.

The second chapter explains the electrochemical technique which used to record the polarization curves of zinc in distilled water in absence and in presence of different percentage of alcohol at different temperature.

The third chapter is devoted for results and discussion In distilled water, it is found that the corrosion potential are nearly the same and around- 30 mV. And the rate of corrosion increases by temperature

In presence of alcohols the corrosion rate is decreased by increasing the percent of alcohol. The decrease in corrosion rate is attributed to (a) Increase of viscosity of solution (b) Solvation of Zn++ (c) Sterric effect of organic mo-ecules to diffusion of Zn++

In case of methanol the corrosion rate is increased at 50% methanol. This is due to change of potential and a decrease in the over potential for cathodic processes as well as adsorption of impurity particles. In case of ethanol the rate of corrosion is increased at first (10-20%). This explained protective of corrosion increases with decreased volume percent of ethanol.

In case of n-propanol, ethylene glycol and glycerol The protection efficiency increases with increase the volume percent at 50-70% The enthalpy was also noticed to increases with decreasing dielectric constant of solventat the same temperature. This is consistent with the fact that, the rate of corrosion decreases with decreasing dielectric constant . The increase of the values of !l.S is attributed to the increase of ion-solvation in water besides electrostatic hydrogen bonds.