Emission rate assessment of airborne brake particles by characterization of the pad and disc surfaces from a pin-on-disc tribometer

Particles from brake, road and tire wear contribute to about half of the emissions (PM10) of particulate traffic pollution. It is estimated that 50 to 70% of the brake debris material is transformed into an emission of polydisperse aerosols. In order to improve the understanding of the brake debris generation and its dependency on the brake material, the wear of a disc and a brake pad from a standard production car were studied. The disc was made of perlitic cast iron with lamellar graphite and subjected to standard braking cycles. Microscopic evaluation was performed on the disc track, as well as analyses by Energy Dispersive Spectroscopy (EDS). Finally, a metallographic section has been made in the longitudinal direction of friction to better understand the morphology. The study focuses on disc surface oxidation and morphology of a thin layer on both disc and pin surface. Particle concentrations increase with the friction power and the area of contact surface. The observations show that the generation of particles can be the result of the oxidation of the disc surface during friction by two- and three-body abrasion when braking.