COLLOIDAL ANTIWEAR ADDITIVES .2. TRIBOLOGICAL BEHAVIOR OF COLLOIDAL ADDITIVES IN MILD WEAR REGIME

The antiwear action of overbased calcium sulfonate detergents in engine oils is studied here by analysis of the wear particles generated during friction tests between two ferrous surfaces. These particles arise from the delamination of the reaction film formed on the rubbing surfaces. This paper deals with the structural and physiochemical changes that the colloidal particles in the contact region have undergone, and which lead to the build-up of the interfacial film. Transmission electron microscopy on the particles shows that the film is composed of calcite crystallites coming from the carbonate cores of the crystallized colloidal particles. Amorphous intergranular zones are responsible for the film ''cohesion''. Electron energy loss spectroscopy shows that the colloidal particles lose some fraction of their organic shell in the contact. The good antiwear properties of these additives is explained by the microgranular structure and the adherence of the surface film.