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

Abstract

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 (Si₃N₄) originally coated with cesium oxytrithiotungstate (Cs₂WOS₃), cesium sulfate (Cs₂SO₄), and a hydrated cesium silicate (Cs₂O·3SiO₂·nH₂O), all applied in a sodium silicate binder (Na₂SiO₃). 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 Si₃N⁴ and Cs₂WOS₃ powders were heated in air to 700°C and analyzed using XPS and Bremsstrahlung-excited AES. It was found that Cs₂WOS₃ accelerates the formation ofSiO₂ on Si₃N₄ under static conditions. These results support our hypothesis that high temperature chemical reactions between the cesium-containing compounds and the Si₃N₄ 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 Si₃N₄

Presented at the 55th Annual Meeting Nashville, Tennessee May 7–11, 2000

KEY WORDS:

• Solid Lubrication
• Silicon Nitride
• Complex Chalcogenides
• Cesium
• Alkali Silicates

Notes

Presented at the 55th Annual Meeting Nashville, Tennessee May 7–11, 2000