Inhibiting effect of silicates on corrosion of low silicon alloyed steels in neutral non-oxidising conditions at 90° C

Abstract

Unalloyed and low alloyed steels undergo predictable uniform corrosion and are potential candidates for high level nuclear waste disposal containers. In this study, low alloyed silicon steel (< 5 wt-%Si) has been tested in a silicate containing corrosive solution at 90 ° C in order to establish whether the addition of silicon to iron would improve the resistance of the surface film to corrosion in an argillaceous (i.e. clayey) soil. Electrochemical tests were conducted for short term immersion of the steel coupons and showed that the addition of silicate to the corrosive solution decreased the corrosion rate, whereas the addition of silicon to the steel increased the critical passivation current peak. A comparison with an unalloyed carbon steel showed that the latter material was more easily passivated than the Si alloyed steel. Weight loss tests were used to study the long term behaviour of the steels in the corrosive medium at 90° C. The inhibiting effect of sodium silicate was significantly increased after some hours of immersion, and the Si alloyed steel was more easily protected than the carbon steel. The surface film consisted of sheet silicate. The influence of the silicate concentration was discussed and correlated to the nature of the dissolved species: silicic acid and/or colloidal particles.