Raman Spectroscopy As An Evaluation Tool Of The Wear Of Graphite Lubricants In Brake Pads

Raman spectroscopy is applied for the non-destructive characterisation of the graphite which is used as solid lubricant in the friction material of semi-metallic brake pads in vehicles. The characteristics (intensity, position, width) of the main Raman bands assigned to vibrational modes of the graphitic honeycomb structure (G-band) and to defects (D-band) are proved useful probes of the quality and wear status of the graphite lubricant because they are sensitive to the structural disorder. It is found that wear of the graphite lubricant proceeds in two stages: transformation of crystalline to nanocrystalline graphite and subsequent amorphisation. Moreover, the intensity of the defect-related D ' peak is also used in order to obtain information about the nature of the defects.