CORROSION-INHIBITORS FOR MILD-STEEL - STANNOUS TIN (SNII) IN ORDINARYPORTLAND-CEMENT

Salts containing divalent tin (SnII) are shown to give a measure of co rrosion protection to mild steel embedded in cement paste. Results of linear polarisation measurements are shown for samples cured at 40-deg rees for up to 240d in pastes containing initially 0-1628mM/l chloride : Sn2+, but not Sn4+, is an effective inhibitor at an initial concentr ation of 200mM/l. However tin solubility pore fluid is very low: less than 0.01mM/l at 60d. It is speculated that tin stabilises the passiva ting layers although no direct evidence for the incorporation of tin i n corrosion product was found by analytical electron microscopy. Other theories of inhibition arc discussed.