Amine Phosphates as Antiwear Additives in Neopentyl Polyol Esters

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Abstract
Dialkyl acid phosphates are effective antiwear agents in neopentyl polyol ester lubricants applied to 440C stainless steel sliding surfaces at low loads, but they promote ester deterioration. Various amine salts of three representative dialkyl phosphates were studied to determine if the adverse effect could be reduced without sacrificing antiwear properties. The amine phosphates were generally highly effective in the low load region in four-ball wear tests. They were at least as effective as the parent acid phosphates and appreciably more effective than tricresyl phosphate. Little effect of amine structure on performance was observed. At a higher load, both the acid phosphates and their amine salts had no beneficial effect on wear. The amine phosphates promoted significantly less deterioration of the base ester under four-ball test conditions (266F) than did the dialkyl phosphates. In oxidation-corrosion tests at 3253, however, they were corrosive to copper and adversely affected ester stability.