Corrosion Inhibition of AA2024-T3 By Sodium Silicate

The mechanism of inhibition of AA2024-T3 by sodium silicate at varying pH was investigated using electrochemical, microscopic and spectroscopic techniques. Polarization curves in naturally aerated solution showed that silicate provides strong anodic inhibition in high alkaline conditions at a threshold concentration of 0.01 M. The largest effect was a 1 V increase in the breakdown potential at a silicate concentration of 0.025 M. The corrosion inhibition mechanism involves the formation of a protective film over the alloy surface by absorption of aluminosilicate anions from solution, as has recently been suggested by others in the literature. At near-neutral pH, silicate partially blocked attack of the intermetallic particles by a precipitation mechanism that resulted in the formation of silica- and silicate- based derivatives. In acidic solution, activation of the aluminum surface promoted the formation of a mixed silica/aluminosilicate film over the surface that was porous in nature, providing very little corrosion protection.