Surface segregation and oxidation of Ti in a V–Ti alloy

The oxidation and reduction of surface oxides of the V–4%Ti alloy were examined by X-ray photoelectron spectroscopy. A specimen sheet of the alloy covered by oxide films was heated between 513 and 1223 K for 10 min in vacuum. Vanadium oxides started to be reduced to the metallic state at 673 K owing to oxygen dissolution in the bulk, while titanium remained in oxidized states up to 983 K. Titanium segregated to the surface above this temperature, and the surface concentration reached up to 40% at 1223 K. The specimen surface enriched in Ti was thus prepared and oxidized at 573 and 773 K under oxygen pressures between 10−5 and 10−3 Pa. At 573 K, titanium was selectively oxidized at 10−5 Pa, while vanadium remained in a metallic state. Such selective oxidation of Ti took place also at 775 K under the pressure of 10−4 Pa. Titanium segregating to the surface appeared to provide the barrier effect against tritium inventory and permeation under high temperature, low oxygen partial pressure conditions through selective oxidation.