In recent years, the mechanochemical aspects of ZDDP tribofilm formation have attracted widespread attention. Atomic force microscopy (AFM) experiments showed that ZDDP tribofilm formation rate increases exponentially with temperature and stress. This discovery indicated that ZDDP tribofilm formation is a stress-augmented, thermally activated (SATA) process. The rate constant, k, for a SATA process can be given by a modified form of the Arrhenius equation, which was originally proposed by Evans and Polanyi, but is now usually known as the Bell model: 𝑘 = 𝐴 exp (-