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

Abstract

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.