Abstract
A number of unused and used heavy duty (H. D.) oils were investigated by the electron microscope. Plain oils containing no additives and an oil containing an anti-wear additive were also investigated. No support was found for the suggestion that unused oils containing H.D. detergent additives are colloidal suspensions, as the micrographs were perfectly clear and no particles were found to be present. Two types of particle were found to be present in used H.D. and plain oils. One type of particle was of the order of 0·05 micron (500A***) and tended to arrange itself in chain structures. The other type was very much larger up to several microns in diameter. The two types of particle may have different origins.
It is concluded that the electron microscope is unlikely to provide a very useful means for the inspection of unused H.D. oils and the authors express doubts regarding the validity of an explanation of their successful use based solely on their deflocculating or dispersant action.
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