Friction systems reach high temperatures during braking because they transform kinetic energy into heat. High temperatures jointly with oxygen induce the reactivity of susceptible materials towards oxidation such as the phenolic resin and metal sulphides. The decomposition of the phenolic resin contributes to the decrease and instability of the coefficient of friction and increases the wear of the pad. Thus, the determination of the oxidation reactions is a key point in knowing the depth at which reactivity can take place and understanding the friction behaviour. This study is focused on determining the reactivity through the brake pads pad (NAO Cu-Free formulation) using the oxidation conditions of metal sulphides as a marker. The reactivity characterization through the brake was done using EPMA/WDS and raman techniques, after SAE J2522 and J2707 tests. The results illustrate that there is oxidation underneath the brake pad surface during braking due to the oxygen presence and the high temperatures reached. Depending on the testing schedule the temperature profiles and concentration of oxygen on the pad are different and consequently also is the tribochemistry. In pads tested according to SAE J2707, the tribochemistry is observed in deeper sections than in pads tested according to SAE J2522. The results of this study will help to determine how far from the surface tribochemistry takes place and to understand the behaviour of friction materials.

Rimsa Metal Technology S.A: Mrs. Gabriela Macías Benalcázar, Dr. Carlos Lorenzana