Yasuo Esaki

The antiwear property of zinc dialkyldithiophosphates in used engine oils

Abstract The change in the lubrication properties of vehicle engine oils with driving distance was studied by using a cross-pin type of lubricant tester and a Fourier transform IR spectrometer. The effect of the thermal decomposition of zinc dialkyldithiophosphates (ZnDTPs) on their antiwear property was also examined. The amount of the ZnDTP in engine oil decreased and the amounts of the decomposition products increased with increasing running distance but a good antiwear property was still observed. After 60 h of heating at 135°C, the ZnDTP in sample oils had decomposed into a precipitate and the antiwear property of the oil had deteriorated. With sample oils containing ZnDTP and a detergent or a dispersant, the decomposition products dissolved in the oil and the antiwear property was maintained even after 80 h of heating. The results suggest that the decomposition products of ZnDTPs have a good antiwear property and that the good antiwear property of the used engine oils was retained because of the solubilization of decomposition products into the oil with the aid of a dispersant or a detergent.

The Mechanism of Synergism Between Sulfur- and Phosphorus-Type EP Additives

A synergistic effect was observed for systems of phosphites and sulfur-type additives, while no interaction was observed for systems of phosphates and sulfur-type additives. The mechanism of synergism was studied by EPMA, FT-IR, GC-FPD, and MS. From a synergistic mixture, a new compound containing phosphorus and sulfur was detected. The new compound which was separated by distillation showed good antiwear properties comparable with the synergistic system and was identified as a thiophosphate. The synergism between the sulfur-type additive and phosphite may be caused by the formation of thiophosphate. The chemical reaction between them is discussed and a reaction formula is proposed. Presented as an American Society of Lubrication Engineers paper at the ASLE/ASME Tribology Conference in Atlanta, Georgia, October 8–10, 1985

Attenuated Total Reflection Surface-Enhanced Infrared Absorption Microspectroscopy for Identification of Small Thin Layers on Material Surfaces

Attenuated total reflection surface-enhanced infrared absorption microspectroscopy (micro-ATR-SEIRA) was developed for the identification of sub-mm size and nm-thick layers on material surfaces by using gold island films deposited on the surface of micro-ATR crystals. A thin layer of triphenyl phosphate (TPP) on a poly(tetrafluoroethylene) (PTFE) membrane filter was used to evaluate the enhancement of the absorption bands. Three types of crystals: diamond, silicon, and germanium, were evaluated. Diamond gave the greatest enhancement with a 12 nm thick gold island film. The enhancement factor was 200 times compared to bare diamond crystal, whereas it was 10 times for germanium crystal. This variation of enhancement factor according to crystal types was presumed to be due to the morphology of the gold films on the crystals. We also obtained an enhanced ATR map over an area of approximately 2 × 6 mm for a thin layer (approximately 1 nm thick) of di-2-ethylhexylphthalate on PTFE using gold-coated hexagonal silicon micro-ATR crystals. This micro-ATR-SEIRA technique has major potential for analyzing small and thin substances on material surfaces.

Change of ZnDTP in Engine Oils During Use

Modifications du dialkyldithiophosphate de zinc dans les huiles de moteur pendant le fonctionnement