Plasma and wet oxidation of (63Cu37Zn) brass

A twin study of the oxidation mechanism of (63Cu37Zn) brass foil in oxygen plasma and in alkaline aqueous solution is reported. Brass foil was exposed to low-pressure rf oxygen plasma in given working conditions and the resulting surface was studied by means of linear sweep voltammetry. The plasma oxidation mechanism involves oxygen radicals, and results from their strong oxidising character. The precursor oxide CuxO, Cu2O and CuO were identified in the passive layer, in addition to ZnO. Most of these oxides also form as corrosion products when brass samples are oxidised in alkaline solution. The corrosive process involves oxygen depolarisation, which develops on a 63Cu37Zn brass rotating disc electrode. Complementary investigation performed for neutral 0.5 M NaCl solution results in voltammograms which evidence a four-electron reduction mechanism.