Thermal chemistry of a high temperature solid lubricant, cesium oxythiomolybdate - Part I - Thermo-oxidative stability of Cs2MoOS3

Cesium oxythiomolybdate (Cs2MoOS3) is a potential high temperature solid lu bricant. It undergoes complex oxidation reactions at elevated temperatures, but continues to provide lubrication above the oxidation temperature. Ther efore, in order to determine the nature of the lubricant at elevated temper ature, it is necessary to understand the thermal chemistry of Cs2MoOS3 in a n air environment. The thermo-oxidative stability of Cs2MoOS3 was evaluated between room temperature and 800 degreesC in air. Melting and phase transi tion temperatures were determined. X-ray photoelectron spectroscopy, micro- Raman scattering and x-ray diffraction were used to identify the chemical s pecies evolved at increasing temperatures. As-received Cs2MoOS3 was not pur e. It also contained cesium molybdates, molybdenum oxides, and Cs2SO4. Betw een 300-400 degreesC, the material began to decompose forming Cs2SO4 and Mo S2. Between 400-600 degreesC, Cs2MoOS3 also formed cesium molybdates and mo lybdenum oxides. In addition, the Cs2SO4 began to oxidize to cesium oxides (which melted) and SOx gas. Also, MoS2 oxidized to MoO3. At approximately 7 00 degreesC, MoO3 began to sublime. Upon cooling from 800 degreesC, the mat erial was primarily cesium oxides and Cs2MoO4, with small amounts of comple x cesium molybdates and molybdenum oxides. (C) 2001 Kluwer Academic Publish ers.