Lubricating Performance of Organic Sulfides Under Repeated Rubbing Conditions

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Abstract
Repeated four-ball tests of squalane with or without organic sulfides have been carried out to investigate the relationship between the properties of surface film formed on the rubbing surfaces and the lubricating performance of several organic sulfides. With dibenzyl disulfide and dibenzyl monosulfide, friction was remarkably reduced and load-carrying capacity raised in the second run with the additive after the first run without the additive, presumably in which only an oxide film had been formed. In contrast, for diphenyl disulfide, the repetition of rubbing tests, each with additive, was effective. EPMA, XPS(ESCA) and electron diffraction techniques have been applied to examine surface films formed during rubbing process. It is confirmed that the formation of surface films with the optimum composition of oxide and sulfide has brought about the excellent lubricating performance of these organic sulfides.