Cesium oxythiomolybdate (Cs2MoOS3) may be an excellent high temperature lubricant, providing a friction coefficient below 0.2 at 650 degreesC. However, oxidation products provide the lubrication above 400 degreesC. Lubricant effectiveness depends strongly on the composition of the substrate materials in contact, such as Si3N4, suggesting that tribochemical and/or thermal reactions at the interface produce new compounds. The thermo-oxidative stability of Cs2MoOS3/Si3N4 and Cs2MoOS3/SiO2 mixtures have been evaluated between room temperature and 1000 degreesC in air. The transition temperatures and oxidation products were identified. The thermal chemistry of Cs2MoOS3/Si3N4 mixtures was significantly different than that of Cs2MoOS3 alone, largely due to the oxidation of Si3N4 to glassy SiO2. Cesium oxythiomolybdate formed cesium oxides, which melted below 600 degreesC. As SiO2 is formed, the cesium oxides diffused into it, creating a cesium silicate glass. Also, Cs2MoO4 was preferentially formed over complex cesium molybdates and molybdenum oxides. In a tribological application, Cs2MoO4, oxides, and cesium silicate glass may be formed at contacting interfaces from Cs2MoOS3 films deposited on Si3N4 substrates. Lubrication would be provided as the shear strength of these compounds decreases with increasing temperature.