Study of the lubrication mechanism of overbased Ca sulfonate on additives containing S or P

The influence of the addition of overbased calcium sulfonate detergent (OBCaSu) on the antiwear properties of sulfuride olefin (SO) and tricresyl phosphate (TCP) was studied with wear tests and surface analyses. Wear tests were conducted on a four-ball wear test machine. The formation of a protective film on the worn surface was examined using scanning electron microscopy (SEM) and X-ray photoelectron spectrometry (XPS). Test results indicate that OBCaSu can improve the antiwear properties of SO and TCP. Surface analyses found that the lubricating mechanism of OBCaSu and TCP is different from that of OBCaSu and SO. In the case of the lubrication of OBCaSu plus SO, the improved antiwear property is caused by the formation of a surface deposition film containing CaCO₃ from the OBCaSu and the neutralization of OBCaSu, which could prevent excessive corrosion wear. In the case of the lubrication of OBCaSu plus TCP, calcium phosphate was formed and incorporated into the surface film, which possesses good antiwear characteristics.