Electron Microscopic Characterization of the Brake Assembly Components (Disc and Pads) from Passenger Vehicles

The present work focuses on a detailed analysis of new and used braking friction partners (discs and pads) in order to provide a comprehensive characterization of the source of the airborne particles formed during braking. Scanning electron microscopy (SEM) combined with energy dispersive X-Ray analysis (EDX) was applied to investigate the new brake disc and new and used brake pad components of a passenger vehicle. The pads include at least 21 different substances, involving carbonaceous particles, oxides, sulfides, sulfates and silicates of Al, Si, K, Ca, Ti, Fe, Zr, Sn, less Mg, Ba, Na and, rarely, Bi and Zn, as well as K-titanate. Aramid and phenolic resin are also present, enriched toward the metal interface. The size of the pad constituents extends over a very wide range, from hundreds of mu m to a few mu m, and goes down to hundreds of nm and, rarely, tens of nanometers. Carbonaceous particles with sizes down to a few tens of nanometers occupy ca. 16% of the total of the pad constituents. Abundant Zr-bearing phases, as well as various other phases involving S, Ca, Mg, Si, Ti and, to a lower extent, Ba and Fe in different combinations, constitute the pad main matrix.