Molybdenum oxide based conversion coatings have been formed on the surface of the depleted uranium-0.75 wt.% titanium alloy and the coating structure was found to undergo changes as it ages. Raman and Fourier transform infrared (FT-IR) spectroscopies have been performed to examine these changes. Raman spectroscopic measurements indicate that the coating is based on an octamolybdate structure and FT-IR experiments show that uranyl hydroxide is present in the as-made coating but no longer apparent in the aged coatings, supporting the proposed mechanism describing the aging of the coating. Both techniques show that none of the molybdenum is in the form of tetrahedral molybdates. (c) 2006 Elsevier Ltd. All rights reserved.