PARAMAGNETIC SPECIES IN I C ENGINE TOP RING ZONE LUBRICANT SAMPLES/

Samples of formulated lubricant have been obtained from the top piston ring zone of a standard operating petrol test engine, the Petter W-1. ESR spectra of samples frozen immediately and also those allowed to s tand at room temperature show a range of paramagnetic features, some o f which interconvert with change in temperature and sample history. Th e ESR spectra of any organic radicals are absent but a 'radical' centr e is identified as arising from amorphous carbon. In contrast, various metal centres are identified, Fe-III high-spin centres decaying to lo w-spin Fe-III centres. C-II and Mn centres are also identified with hy perfine coupling to N-14 and to Cu-II. It is argued that the hyperfine interactions from ligands to these centres may result from decomposit ion products of the additive pack components, for example N-14 hyperfi ne interaction to the Cu-II from the nitrogen-functionalized dispersan t and sulphur-centred ligands generated by the decomposition of the zi nc dialkyl dithiophoshate antioxidant/anti-wear additives. (C) 1997 El sevier Science Ltd.