The roll of the carbonate size and morphology (amorphous or crystalline) in an overbased detergent on the surface rheology in a tribometer was invesigated. From XPS analysis of the wear scars produced in the Reichert test, it appears that OBCaS (amorph) and OBCaS (cryst) both form thin layers of CaCO3 on top of a thicker layer of CaO (from CaCO3 decomposition) on the surface of the test piece. Additionally, we examined the morphology of the Ca and S films using Auger Electron Spectroscopy (AES). In the presence of sulfurized olefin, additional AES analysis reveals that a layer of both S and Ca cover the surface, where the Ca is more prevalent and evenly coated and the S is mottled and lower in concentration. From AES analysis of selected regions, the surface either possessed high S or high Ca concentrations, but never both together. We have shown that crystalline overbased sulfonate detergents product possesses excellent Reichert test results over the conventional amorphous overbased materials, and subsequent X-Ray Photoelectron Spectroscopy (XPS) analysis revealed that thicker Ca and S films were observed on test specimen containing crystalline OB sulfonate compared to amorphous OB sulfonate.
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