The surface chemistry of chloroform as an extreme-pressure lubricant additive at high concentrations

Carbon tetrachloride is an extremely good extreme-pressure (EP) lubricant additive at low concentrations (< 3 wt% chlorine) since it can react to form a high-melting-point Fe3C antiseizure layer. In contrast, small hydrogen-containing additive molecules (CH2C12, CHC13) decompose to form FeC12 which melts at ,,~940 K and limits the maximum seizure load to N 3500 N as measured in a pin and v-block apparatus. However, both thermodynamic calculations and results of a Mfssbauer analysis of an iron foil heated in CHCI3 at 830 K indicate that iron carbide can be formed from chloroform. In addition, it is also found in that case that a plot of seizure load versus concentration, after initially forming a plateau, once again increases with higher additive concentrations (> 4 wt% chlorine) in accord with the idea that a higher melting point carbide film can be formed. It has been shown previously that asymptotes in the plot of removal rate versus applied load correspond to melting of the interracial anti-seizure film. When using 9.0 wt% chlorine from chloroform as the additive, a drastic increase in removal rate is found at an interfacial temperature of-~ 940 K corresponding to the melting of FeC12 and an additional asymptote is evident at ,-~ 1500 K due to the melting of Fe3C in accord with the thermodynamic and M6ssbauer results.