In situ observation of surface -OH and -OD on lithium oxide

To elucidate the tritium release mechanism from the surface of solid breeding materials, surface -OH and -OD on Li2O were studied at high temperature up to 400 C and under controlled H2O (D2O) vapor pressure or H2(D2) partial pressure by using a diffuse reflectance method of FTIR (Fourier transform infrared absorption spectroscopy). During the drying process of Li2O, a large peak of precipitated LiOH was observed at 3662 cm-1. When D2O vapor was added to a concentration higher than the precipitation limit, the O-D peak from LiOD was observed at 2696 cm-1. Below the limit D2O vapor pressure, absorption peaks of isolated -OD on the surface were found at least at two positions: 2748 cm-1 and 2717 cm-1. This experimental fact shows that the surface is not homogeneous for D2O adsorption. The peaks shifted to the lower wave numbers with the precipitation of LiOD at lower temperature. When D2 was added to He+D2O sweep gas, the intensity of the peak from isolated -OD became higher, indicating D2 is dissociatively adsorbed on the Li2O surface to produce -OD. ((orig.))