Solid Lubrication of Silicon Nitride with Cesium-Based Compounds: Part II - Surface Analysis

Energy dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), and Auger electron spectroscopy (AES) were used to characterize the wear surfaces of selected samples from Part 1 of the authors study. Results are presented for films generated on silicon nitride (Si 3 N 4 ) originally coated with cesium oxytrithiotungstate (Cs 2 WOS 3 ), cesium sulfate (Cs 2 SO 4 ), and a hydrated cesium silicate (Cs 2 O·3SiO 2 ·nH 2 O), all applied in a sodium silicate binder (Na 2 SiO 3 ). Results show the presence of mostly Si, O, and Cs within the wear tracks of post-tested specimens. In some cases, W and S were not detected on samples that originally contained these elements, suggesting that decomposition had taken place. To simulate the reactions that might occur in a tribo-contact, mixtures of Si 3 N 4 and Cs 2 WOS 3 powders were heated in air to 700°C and analyzed using XPS and Bremsstrahlung-excited AES. It was found that Cs 2 WOS 3 accelerates the formation ofSiO 2 on Si 3 N 4 under static conditions. These results support our hypothesis that high temperature chemical reactions between the cesium-containing compounds and the Si 3 N 4 surface form a lubricious cesium silicate film. A mechanism is proposed based on the glass-modifying tendency of alkali metals and the hot-corrosion of Si 3 N 4 Presented at the 55th Annual Meeting Nashville, Tennessee May 7-11, 2000