SURFACE-CHEMISTRY AND EXTREME-PRESSURE LUBRICANT ADDITIVE PROPERTIES OF CHLOROFORM ON IRON

The growth kinetics and composition of films formed by the thermal dec omposition of chloroform are very similar to those for methylene chlor ide reported previously [P.V. Kotvis et al., Wear 147 (1991) 401; 153 (1992) 305; Appl. Surf. Sci. 40 (1989) 213; Langmuir 9 (1993) 467], bo th depositing films that consist of an iron halide and incorporating c arbon. Raman spectroscopy suggests that less carbon is incorporated in to the layer grown from chloroform, an effect that is proposed to refl ect the initial carbon: chlorine ratio in the precursor reactants. The tribological properties measured using a pin and V-block apparatus fr om the seizure load as a function of the additive concentration are ve ry similar in both cases, showing an initial increase in seizure load up to additive concentrations of approximately 2 wt% of chlorine and r emaining constant thereafter, the main difference being that the satur ation seizure load is higher when using chloroform than when methylene chloride is the additive. This effect is explained since the interfac ial coefficient of friction of films grown from chloroform are lower t han those from methylene chloride so that, for a particular applied lo ad, the interfacial temperature is lower in the former case. Since the seizure load in the plateau region (at high additive concentrations) corresponds to the load at which the interface reaches the melting poi nt of FeCl2, this temperature is attained at a higher load with CHCl3 than CH2Cl2. It is possible that the amount of carbon incorporated int o the iron halide anti-seizure film affects the resulting coefficient of friction.