Corrosion Behavior of Nickel in Methanol

Corrosion behavior of pure nickel in methanol containing different concentrations of water, chloride, and H⁺ ions has been studied using the potentiodynamic technique. Nickel does not exhibit passivity in methanol containing less than 0.5% water. The passive film on the metal is found to be stable in a large range of anode potentials in methanol containing more than 0.5% of water. The chloride ion is found to induce pitting, and this is more pronounced in the presence of the H⁺ ion in the solution. The addition of water does not significantly aid passive film formation in the presence of the chloride ion. At pH 8, the transpassivity of the passive film occurs at a potential of 1.20 V (SCE), which falls steeply with a decrease in the solution pH. The addition of sulfuric acid in methanol strongly activates the metal dissolution. An increase in temperature is found to enhance the primary passivation potential and critical current density (CD), but the pitting potential remains unaltered. Plotting of the logarithm of the critical CD with an inverse of temperature yields a straight line with the apparent activation energy and temperature coefficient equal to 13.7 and 3.33 kcal/mol, respectively.