Inhibiting properties of phosphines against zinc corrosion in acidic media

Uniform corrosion of zinc in aqueous deaerated sulphate solutions can be greatly increased by the use of organic phosphines and diphosphines. The inhibition mechanism in sulphuric acid solutions has been studied by conducting electrochemical and weight loss experiments. Adsorption of inhibitor on to the metal surface through the phosphorus atoms is responsible for the efficiency of the monophosphines. These phosphines act by producing equal coverage of the anodic and cathodic areas by the non-protonated form of the molecule, while the protonated form has an accelerating effect on the cathodic partial reaction. Diphosphines operate as mixed inhibitors and are more effective than monophosphines owing to their chelating properties on the zinc surface.