Preparation and characterisation of pitch-based granular composites to be used in tribological applications

Four pitches (a commercial impregnating coal-tar pitch, an air-blown pitch and two thermally treated coal-tar pitches) and four granular carbons (graphite, anthracite, green petroleum coke and foundry coke) were used to prepare carbon composites to be tested as carbon brake pads. The pitch to carbon ratio was adjusted to optimise the compressive strength of the composites. The optimum pitch content greatly varies depending on the carbon used, ranging from the 25-45 wt.%. The frictional behaviour of the materials was mainly governed by the type of granular carbon used. Graphite renders composites with low and stable friction coefficient while, on the other side, anthracite provides high and unstable friction coefficient. In general, composites prepared in this work exhibit lower wear rates and similar friction coefficient variations when compared to two commercial brake lining materials.