ESCA investigation of the reaction products formed on titanium exposed to water saturated bentonite clay

Titanium is one of the materials proposed in the Swedish program for the final containment of spent nuclear fuel. In the present investigation, the final repository environment was simulated on the laboratory scale by embedding titanium and a Ti-Pd alloy in dense, water-saturated bentonite clay. The temperature was 950C and the exposures lasted between 4 months and 2 years. Analysis was performed using ESCA combined with ion etching. The reaction products formed on the surface consists of TiO2. Montmorillonite - the main constituent of bentonite - is incorporated in the oxide. Suboxides exist near the oxide/metal interface. The oxide thickness is in the range 70-100 A. The oxide growth between 4 months and 2 years is small. No significant influence of Pd could be noted. If it is assumed, that the oxide growth follows a logarithmic law, the expression giving the thickest oxide is y = 5.5 1n t (where y is the oxide thickness (A) and t is the exposure time (s))