Tritium Retention in Hexavalent Chromate-Conversion–Coated Aluminum Alloy

In this work, Aluminum 6061-T6 samples were subjected to MIL-DTL-5541F type-I, class-3 anodic coatings, where a yellow irradiate finish was achieved. Both chromate-conversion coatings (CCCs) and unmodified samples were exposed to deuterium-tritium (PT = 0.51 atm) gas for 24 h at room temperature. Following loading, the samples were subjected to one of two desorption techniques: temperature-programmed desorption or a surface stripping technique. The results show that chromic-acid anodizing of aluminum dramatically increases the total quantity of tritium retained by the treated surface as compared to unmodified aluminum. X-ray photoelectron spectroscopy and scanning electron microscopy studies of both treated aluminum and unmodified samples indicate that the CCCs contain significant quantities of hydrated chromium. Using transmission electron microscopy, the surface is shown to have significant cracking and fracturing of the film and leads to a highly grained and porous surface. Such surface defects coupled with the vast quantity of hydration sites are likely reasons for the increased retained tritium inventory observed for CCC samples. Because of the physical and chemical properties of unmodified CCC samples, they are not suitable for use in tritium environments.