Non-Stoichiometry and Vaporization Characteristic of Li2.1TiO3.05 under Hydrogen Atmosphere

Li2TiO3 is one of the most promising candidates among the proposed solid breeder materials in fusion reactors because of its chemical satiability. Addition of H2 to inert sweep gas has been proposed for enhancing the release of bred tritium from breeder material. However, the mass of Li2TiO3 was found to decrease with time in the hydrogen atmosphere. This mass-change indicates that the oxygen content of the sample decreased, suggesting the change from Ti4+ to Ti3+ and the partial pressures of Li containing species were increased. In order to control the mass-change at the time of high temperature use, the development of Li2TiO3 which has Li2O additive is needed. Furthermore, since Li2TiO3 is reduced in hydrogen atmosphere, it is important to investigate the reduction characteristic with Li2O addition. In the present paper, the non-stoichiometry and vaporization characteristic of Li2TiO3 added with Li2O have been extensively investigated by means of thermogravimetry and atmosphere-controlled high-temperature mass spectrometry. In the case of the Li2TiO3 samples used by the present study, Li2CO3 and TiO2 powders were mixed in the proportions corresponding to the molecular ratio Li2O/TiO2 of either 1.00 or 1.05. These samples are designated as L100 (Li2TiO3), and L105 (Li2.1TiO3.05), respectively. In thermogravimetry, the masses of L100 and L105 were found to decrease with time in the hydrogen atmosphere, then to increase after the change of the atmosphere from hydrogen to oxygen. The color was observed to change from white to thin light-brown under the hydrogen atmosphere. This color-change indicates that the oxygen content of the sample decreased, suggesting the change from Ti4+ to Ti3+. Further, L105 has fewer oxygen defects than L100. L105 has the smaller mass of TiO2 in Li2TiO3, so that the order of oxygen defects was as follows, L105 < L100. An atmosphere-controlled high-temperature mass spectrometer has provided the vapor pressure data for L100 and L105, under the conditions of D2 atmospheres. In case of adding D2 gas, Li(g), LiOD(g), Li2O(g) D2(g) and D2O(g) were identified as the vapor species. The sum of the partial pressures of Li containing species was calculated. Its order under D2 atmospheres was as follows: L105 > L100 (1093 - 1473 K) L105 = L100 (<1093 K). The overall results suggest that the Li2O additives are able to control not only the amount of oxygen defects but also the partial pressures of Li containing species. (author)