Identification of carbon forms and other phases in automotive brake composites using multiple analytical techniques

One of the most important parameters characterizing the performance of brake materials is their formulation. Therefore, the precise analysis of brake materials is needed both to investigate formulation-performance relationship, and to maintain quality control. A typical brake composite contains more than ten phases (components), either crystalline or amorphous. Combinations of X-ray diffraction (XRD), light microscopy (LM), and scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDX) are used to identify the phases present. However, the combination of these methods is insufficient for precise resolution of all phases in brake composites. The large number of phases can cause the overlapping of peaks in the XRD pattern, making them difficult to identify. This problem has been overcome by using density gradient centrifugation (DGC) to separate the powdered sample into density fractions that are easier to identify. The results of this study show that a combination of applied techniques can be effective in identifying brake formulation. Because carbon materials are significant components of brake composites, special attention was given to the discrimination of these components such as coke, graphite, and aramid fibers.