THE THERMOCHEMISTRY OF THE REACTION OF LITHIUM ORTHOSILICATE WITH HYDROGEN

The formation of an oxygen-deficient layer at the surface of lithium o rthosilicate by reaction with hydrogen is confirmed by the following f indings: i) formation of hydrogen by reaction with water vapor, ii) up take of oxygen, and iii) increase in lithium partial pressure and decr ease in oxygen partial pressure relative to conditions in the absence of hydrogen according to p(Li)(4)p(O-2)(-1). The partial pressures of D-2, D2O, Li, and LiOD in the saturated vapor over Li4SiO4 were measur ed as function of temperature under steady state conditions reached in the late phase of long-term experiments. The employed temperature ran ge, e.g. 945-1173 K, is in or close to the region of interest to blank et technology. From the data on the temperature dependence of the rati o p(D2O)/p(D-2) an enthalpy of reaction for the formation of the reduc ed layer on lithium orthosilicate by reduction with deuterium of Delta H-1059K(degrees) (37.0 +/- 0.2) kJ/mol is calculated.