The reaction of the oil additive tricresylphosphate on steel: The solution to an enduring 100-year-old mystery

Tricresyl Phosphate (TCP) is an exceptional additive for improving tribological efficacy. In this paper, we propose a comprehensive reaction mechanism based on the transient states in the reaction, using Raman spectra collected during the reaction, along with general and optical observations. Based on nanomechanical testing, we also clarify the mechanical mechanism by which the TCP-derived tribofilms protect a steel surface. The TCP reaction is catalyzed on the steel surface, forming an amorphous carbon (a-C) network. Initially, this network is heavily sp2-bonded, 2-bonded, but it later evolves into a more sp3-bonded 3-bonded network. The reaction begins with radical formations, causing the loss of C-H - H bonds. This leads to the forming of a carbon network that cross-links the TCP's ' s benzene rings. Due to the presence of steel, the reaction can occur at temperatures as low as 75 degrees C. The thermal mechanism of TCP's ' s action and its resulting tribological efficacy have been extensively studied. The key takeaway from this mechanistic approach is that TCP's ' s success as an additive comes from its ability to cross-link between aromatic rings at low temperatures on steel to form extended sp2-rich 2-rich a-C networks. These carbon networks protect the steel surface due to their viscoelastic properties. Our research provides a comprehensive understanding of TCP's ' s reaction mechanism and tribological efficacy, offering valuable insights for further studies and practical applications.