Figure shows the change in the total number of C-O and P-O bonds with sliding time for an intermediate temperature (500 K) and pressure (3 GPa). For the Fe 3 O 4 (001) surfaces, bonds with surface oxygen atoms are included in the analysis. Solid lines represent the total change in the number of bonds compared to the TCP molecules, dotted lines show the contribution from bonds in TCP that are broken, and dashed lines show new bonds that are formed. For all the surfaces, approximately five times as many P-O bonds are broken than C-O bonds, suggesting that P-O cleavage dominates over C-O cleavage. This is expected based on previous MD simulations and experiments of the thermal decomposition of TCP for triaryl phosphates. Conversely, in previous NEMD simulations of trialkyl phosphates confined between α-Fe(110) surfaces, approximately twice as many C-O bonds were broken than P-O bonds. The decomposition mechanism is therefore affected by the much stronger C-O bonds in triaryl phosphates relative to those in trialkyl phosphates. Moreover, unlike triaryl phosphates, some alkyl intermediates formed by C-O cleavage in trialkyl phosphates, such as butyl chains, can readily undergo β -hydride elimination reactions on ferrous sur- faces to produce gaseous olefins. In Figure , the number of C-O and P-O bonds broken for the α-Fe(110) and Fe 3 C(010) surfaces is similar, but fewer bonds are broken for the Fe 3 O 4 (001) surfaces.