Preheating temperature effect on tritium retention in VPS-W

The deuterium retention behavior for the Vacuum Plasma Spraying (VPS) tungsten (W) coating was studied to demonstrate the tritium retention as a function of heating temperature. It was found that two major deuterium desorption stages were observed at the temperature regions of 400 - 700 K (Stage 1) and 900 - 1100 K (Stage 2), considering that Stage 1 was linked to the desorption of deuterium trapped by near surface and intrinsic defects, and Stage 2 was related to the desorption of deuterium bound to impurities as C-D bonds. By heating the sample above 673 K, the major peak of C-1s was shifted from C-O bond to C-C bond, where the retention of deuterium as Stage 2 was increased. Therefore it was indicating that the hydrogen isotope retention was controlled by the amount of C-C bond in VPS, most of which was contaminated during the VPS coating process. The comparison of several samples (VPS-W with shading, VPS-W without shading and Polycrystalline W (PCW)) shows that the carbon impurity has a large affinity with deuterium and make stable trapping states compared to that with intrinsic defects and grain boundaries. However, most of them was reduced by heating at 1173 K. Therefore, heating treatment is quite important to get rid of carbon impurities and refrain higher tritium retention in VPS.