Effect of pH on Mg(OH)2 film evolution on corroding Mg by in situ kinetic Raman mapping (KRM)

A C T Mg(OH) 2 films evolution at initial stages of Mg aqueous corrosion was studied by in-situ Raman spectroscopy adapted for kinetic Raman mapping (KRM). Crystalline Mg(OH) 2 (brucite) formed in situ from the first minutes of reaction. KRM evidenced a threshold-like Mg(OH) 2 growth kinetics for areas where black filaments were later formed, linear kinetics for visually intact areas at pH 9-10 and parabolic law for intact areas at pH > 11. The Mg(OH) 2 morphology expected from in-situ Raman scattering of surface OH groups correlated well with ex-situ microscopic observations. A dissolution-precipitation model of Mg(OH) 2 layer evolution was applied to explain the experimental observations.