Spectromicroscopy of tribological films from engine oil additives. Part I.Films from ZDDP's

Antiwear films formed from pure neutral alkyl- and aryl-ZDDP's, and a comme rcial ZDDP, have been studied with high resolution synchrotron-based photoe mission spectromicroscopy with a new instrument, MEPHISTO. Good P L-edge XA NES spectra have been taken on areas between 12 and 400 mu m(2), and good i mages of phosphates and ZDDP have been obtained at similar to 1 mu m resolu tion on both smooth and rough steel. These spectra, and corresponding image s, show immediately that both the chemistry and the morphology of the alkyl and aryl films are very different. The alkyl film contains a range of smal ler and larger protective polyphosphate pads from a few to similar to 25 mu m(2) in area. We have shown that the chemistry of small and large pads are different. The large pads contain very long chain polyphosphate; while the smaller pads contain short chain polyphosphate. The aryl films contain ort ho- or pyro-phosphates, are much thinner and more uniform, with obviously m ore streaking from initial wear, and no obvious protective pad formation. A ntiwear films generated from the commercial ZDDP, rubbed in base oil, show that the long chain polyphosphate is converted to ortho- or pyro-phosphate, but the amount and distribution of phosphate does not change noticeably. T he antiwear films are remarkably stable physically.