Dr. Roberto Dante, Quartz, ITALY

Ing. Edoardo Cotilli, Quartz S.r.l.s.u., ITALY

Ing. Michael Conforti, Quartz S.r.l.s.u., ITALY

Ing. Mario Cotilli, Quartz S.r.l.s.u., ITALY

Ing. John Oleary, Applus IDIADA, UNITED KINGDOM

Antimony trisulfide is widely used in friction materials to stabilize the coefficient of friction in synergy with lubricants and abrasives. It was found that Sb2S3 favors the formation of a steady rotor tribolayer. However, Sb was almost no present in the rotor tribolayer after dynotests, such as the wear test VW TL110, and another test specifically used to collect wear debris, in a low steel formula containing the 5 wt% of Sb2S3 . Indeed, in wear debris Sb, as well as on the rotor surface, was actually found as sulfide Sb2S3 and even as metallic antimony. It seems that Sb2S3 decomposes to metallic antimony, as supported also by previous thermal gravimetric and scanning calorimetry studies, which sublimates due to the high contact temperatures achieved during the braking applications skipping the stage of oxide formation. In contact asperities the concept of temperature can be used only with approximation, since reactions and transformations under friction are activated by friction work (which breaks bonds) rather than only direct heat, and follow different pathways from those occurring in standard thermal chemistry. Apart as working as a coadjuvant of lubricants for its ability to create a steady tribolayer, the mechanism of action of Sb2S3 seems to be linked to sublimation as a metal from the tribolayer and wera debris. These facts open a new sight on the mechanism of action of this common ingredient of friction materials. The performance of antimony trisulfide, which provides a steady coefficient of friction and tribolayer, seems to be linked to its instability. The deepening in its peculiar tribochemistry and tribophysics can help to develop valid alternatives.