Chemical Reactivity and Load Carrying Capacity of Lubricating Oils Containing Organic Phosphorus Compounds

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Abstract
The work described in this paper is a study of the high temperature corrosion reaction of iron in oils containing phosphorus compounds such as the phosphite, phosphate, thiosulphate, acid phosphate and acid phosphite, by using the hot-wire method. The neutral type esters show very little chemical reactivity towards iron in marked contrast to the very high reactivity of the acid type esters and thiophosphite. X-ray analysis revealed basic iron phosphate, 2FeFe4(PO4)(OH)5, and iron sulfide as the main reaction products for the neutral type and acid type esters and thiophosphite, respectively. The surface polishing action, peculiarly attributed to phosphorus compounds, could not be confirmed in the present work. The results from X-ray analysis seem to support the iron phosphate lubrication mechanism of phosphorus type EP additives. Some considerations are given for the correlations between the chemical reactivity, load carrying capacity and anti-wear property of oils containing phosphorus compounds. As to the lubrication characteristics of chloride, sulfide, phosphide and phosphate films, some postulations are made.