Thermal oxidation of titanium to improve corrosion resistance in boiling nitric acid medium

Commercially pure titanium (Cp-Ti) is being used as structural material for fabrication of dissolver in the reprocessing of carbide fuel from fast breeder test reactor. Thermal oxidation of titanium is one of the most simple and feasible options to extend the life of such critical components. In the present study thermal oxidation of titanium has been carried out at 923 K for 96 h. The thermally oxidized Cp-Ti samples were characterized by SEM, XRD, microscratch test and profilometry. Corrosion studies were carried out in boiling nitric acid medium as per ASTM A262 practice-C test and three phase corrosion test and the results were compared with Cp-Ti and Ti-5Ta-1.8Nb alloy. ASTM A262 practice-C test revealed reproducible outstanding corrosion resistance of thermally oxidized Cp-Ti compared to Cp-Ti and Ti-5Ta-1.8Nb alloy. Three phase corrosion test results also indicated better corrosion resistance of thermally oxidized Cp-Ti. The protective thick rutile TiO2 oxide layer with nano-rod structure formed on the surface improved the corrosion resistance of thermally oxidized Cp-Ti in boiling nitric acid as evident from SEM and XRD results. The hardness of thermally oxidized Cp-Ti sample was found to be 2.5 times higher than that of Cp-Ti and the surface roughness of the thermally oxidized Cp-Ti samples was found to be smooth before and after corrosion when compared to the as-polished surface. The corrosion resistance of the thermally oxidized Cp-Ti samples can be further improved by optimizing the parameters to achieve good adhesion strength. The paper highlights the results of the present investigation.