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A strong synergism between overbased sulphonate (OBS) and zinc dialkyldithiophosphate (ZDDP) in a proven diesel engine oil formulation has been reported in an earlier communication.1 In continuation of these studies, the effect of different types of dispersant, of varying nitrogen content, and an antioxidant, on a synergistic combination of OBS‐ZDDP has been investigated. Both detergency and dispersancy of the optimised formulation were improved with high nitrogen‐content dispersants, which also increased strongly the wear tendencies. The antioxidant, though it improved detergency, did not show any positive effect on antiwear performance. Detailed IR and 31p‐NMR spectroscopic analyses on interactive additive pairs, namely, ZDDP‐PIBS and ZDDP‐antioxidant, indicated the formation of association complexes and hydrogen bonding respectively.

Transformation characteristics of a Cu-27Ni-2Cr alloy were studied on ageing in the temperature range of 773 to 1073 K, by means of X-ray diffraction and transmission electron microscopy. It was concluded from morphological features that the alloy undergoes spinodal decomposition and the coherent spinodal was estimated to be 946 K. Yield stress increment on ageing was found to follow monotonically the strain amplitude and to be independent of the wavelength of composition modulation.

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