Mercapto-benzothiazole as corrosion inhibitor for single crystalline copper in sulphuric acid

Abstract

The corrosion rates of copper single crystal {100}, {110}, and {111} planes have been determined in stirred 0·1 M H₂SO₄ solutions containing various concentrations (10⁻⁶–10⁻³ mol l⁻¹) of mercapto-benzothiazole (MBT) by weight loss and polarisation techniques. The corrosion rate, which was controlled by surface reaction, was found to be a function of crystallographic orientation, temperature, and MBT concentration. The stabilities of the three crystal orientations in pure acid were found to be {111} > {100} > {110}. However, at the critical MBT concentration (10⁻³ mol l⁻¹) the stability order was found to be {110} > {100} > {111}. The observed corrosion data indicated inhibition by surface adsorption of inhibitor molecules, following the Bockris-Swinkels adsorption isotherm. The weight loss and polarisation techniques gave similar inhibitor efficiency values. The order of stability of the crystal planes was further confirmed by a thermodynamic study of inhibitor molecule adsorption. The formation of MBT-Cu(I) films from the surface reaction of cuprous ions with adsorbed MBT acts as a barrier against the corrosive environment.