Towards a better understanding of the reaction between metal powders and the solid lubricant Sb2S3 in a low-metallic brake pad at high temperature

Abstract During braking, high temperatures can be generated on the contact surfaces and inside the brake pads. Solid lubricants, i.e., metal sulphides, play an important role in brake performance, but they can react, oxidise or decompose with exposure to temperature, modifying their tribological properties. This paper investigates the chemical reactions between different metal powders (Cu, Fe, Sn and Zn) and Sb 2 S 3 that take place in a low-metallic brake pad during braking in conditions were high temperature is generated. The reaction products were characterised by SEM–EDS and the glancing XRD technique. Moreover, thermal treatments (in air and argon) of binary mixtures, containing the same weight ratio of these metal powders and Sb 2 S 3 contained in the brake pad, were carried out and analysed via DSC–TGA and XRD techniques. The paper finds that the reaction features and reaction products depend on the temperature generated during braking, the specific combination of metal/lubricant and the atmosphere conditions (oxidant or inert). In general, the reaction products are a combination of an intermetallic (metallic antimonide) and a metal sulphide (from the metal powder), which can be found both on the surface and inside the brake pad.