Interference between Tin Sulfides, Graphite and Novolak Oxidation

Tin sulfides (SnS and SnS₂), represent a safer and greener alternative to other metal sulfides such as copper sulfides, and MoS₂ etc. Their behavior is usually associated to that of solid lubricants such as graphite. A mixture of tin sulfides, with the 65 wt% of SnS₂, has been characterized by scanning electron microscopy and by thermal gravimetric analysis (TGA). In order to investigate the effect of tin sulfides upon two crucial friction material ingredients, two mixtures were prepared: the former was made by mixing tin sulfides with a natural flake graphite and the latter was made mixing tin sulfides with a straight novolak. They were analyzed by TGA and differential thermal analysis (DTA) in both nitrogen and air. Some interferences were detected between tin sulfides and graphite in air. However, the oxidation of tin sulfides was concomitant with that of the novolak so that the resin onset decomposition-oxidation was considerably shifted to higher temperatures allowing the resin to work as a binder also in a critical temperature range. This is an additional benefit of tin sulfides apart acting as a solid lubricant.