Enhanced passivation of alloy corrosion-resistant steel Cr10Mo1 under carbonation — Passive film formation, the kinetics and mechanism analysis

It has been repeatedly reported that Cr-series alloy steels have enhancing passivation under carbonation (within alkalinity range), which is diametrically opposed to plain carbon steel. This work investigated the composition and structure depth profiles of passive film formed on alloy corrosion-resistant steel Cr10Mo1 in simulating concrete pore solutions of different pH (13.3, 12.0, 10.5 and 9.0) by X-ray photoelectron spectroscopy (XPS), and analyzed the kinetics of the passive film growth and formation influenced by the pH through current transient analysis. The results stated that the growth and formation process of passive film on the steel could be explained using dissolution-precipitation reaction mechanism. When exposed to an alkaline medium, the metal first incurs rapid anodic dissolution and releases metallic cations into the electrolyte before the passive oxides/hydroxides precipitation. Decreasing pH promotes excessive anodic dissolution of the metal and more metallic cations are released into the solution, resulting more Cr species enriched in the film layer for their high stability insensitive to lower pH although Fe species become soluble under carbonation. This contributes to the formation of a thicker passive film with higher corrosion resistance, providing the steel enhanced passivity in less alkaline environments.