Effect of molybdate ions on the corrosion behaviour of Ti alloys

Titanium alloys are extensively used in power, chemical and petroleum indus tries as constructional materials for vessels and heat transfer tubes. More over they are candidate materials for nuclear waste disposal. These alloys have superior resistance to localized forms of corrosion compared to stainl ess steels and Ni-base alloys. However, this resistance is not as remarkabl e in crevice corrosion conditions in some aggressive media. Electrochemical corrosion tests were conducted on two ASTM Ti grades namely, Ti-2 and Ti-1 2 in extremely low pH acidic environment. Results indicated that Ti-2 has l ess resistance to both general and crevice corrosion attack than Ti-12. Bot h alloys possess better resistance to general corrosion than to crevice cor rosion. Also, results showed that the molybdate addition improves remarkabl y the resistance of Ti-2 to both types of attack. The increase of molybdate ions concentration from 0.03 mol/L to 0.15 mol/L made Ti-2 to be as resist ant as, or somewhat higher than, Ti-12. The elecrochemical findings were fu rther supplemented by optical examination of the corroded surface.