The passive behaviour of Mg in alkaline fluoride solutions. Electrochemical and electron microscopical investigations

The passive behaviour of pure Mg at 25°C was studied by electrochemical methods in solutions of pH 7–14 containing 0–4 M KF. The dependences of the quasi-steady corrosion current density on pH and [KF] were assessed. Solutions of NaF and NH4F were also tested. The corrosion films were examined by SEM, TEM and AES. Porous, gel-like Mg(OH)2 films were formed in solutions with small, or no, additions of KF. At high [KF], very protective films were formed (corrosion current densities 10−9−10−8Acm−2). The composition of these films was not identified. MgF2 and KMgF3 were identified by electron diffraction in some other corrosion films.