TEM characterization of particulate matter emissions from the bedding stage of a Cu-free brake friction material

Airborne particles in the aerodynamic diameter range of 1-2.5 μm, collected during the dynamometer bedding of a low metallic Cu-free brake friction material, have been investigated using a transmission electron microscopy (TEM) approach. A characterization protocol, based on the combination of imaging, diffraction, and spectroscopy data, has been applied to the particles collected at each bedding stage, to determine the phase and chemical composition of the particles. The results highlight the evolution of the tribological mechanisms occurring during bedding, having important effects on the whole lifetime performances, and are also interesting for developing better friction materials with reduced particulate matter emission, still complying with the required safety standards.