Aluminium-Thiourea Mixtures as Corrosion Inhibitors for Mild Steel in 1·0% NaCl

Abstract

The inhibitive properties of mixtures containing aluminium salts and thiourea (so called aluminium-thiourea inhibitors) have already been investigated in relation to their inhibitive properties towards mild steel corrosion in distilled water and in water of high specific salinity (1·0% Na₂SO₄. This paper reports laboratory test data obtained during further investigations of aluminium-thiourea inhibitors in another corrosive medium, 1·0% NaCl at 20°c and under stagnant conditions. It was found that the corrosion rate of mild steel in sodium chloride solutions can be decreased markedly (by ~ 80%) if aluminium ions are used in the form of a mixture of sulphates and oxychlorides and in conjunction with thiourea, cationic surfactants and reducing agents (SnCl₂). Any change in the composition of the aluminium salts in the mixture, keeping a constant Al³⁺ concentration (for instance a substitution of sulphates/oxychlorides by sulphates/chlorides or chlorides/oxychlorides) reduces the inhibitive efficiency of the formulations tested. The author fails to find a satisfactory explanation of the very specific inhibitive behaviour of aluminium-thiourea mixtures in 1·0% NaCl.