John O. Smith

Antioxidants for High-Temperature Lubricants

Recent changes in the design of aircraft engines have created a demand for lubricants that will perform satisfactorily under conditions far more rigorous than were ever experienced in the past. These increased demands cannot be met by conventional lubricants or by lubricants protected by conventional additives. Among synthetic lubricants being explored as functional fluids in this new area are the polyphenyl ethers. Polyphenyl ethers possess very good high-temperature properties. For example, bis(phenoxyphenoxy) benzenes are oxidatively stable to 500 F and thermally stable to 800 F. This paper summarizes the research aimed at improving the oxidative stability of polyphenyl ethers by the use of additives. It has been found that classic antioxidants such as amines and phenols are ineffective under extreme conditions. Chemical classes such as metal chelates, organometallics, and metal oxides inhibit oxidation of polyphenyl ethers at elevated temperatures. Presented as an American Society of Lubrication Engin...

Antiwear and Extreme Pressure Additives for High-Temperature Lubricants

New aircraft engines require new lubricants that will function under extreme conditions. Synthetic lubricants such as polyphenyl ethers are being explored as functional fluids in this new area. Although the thermal and oxidative properties of polyphenyl ethers are quite good, the lubricity properties are not outstanding. This paper summarizes research done in our laboratory on lubricity additives for polyphenyl ethers. A number of additives have been found to be effective. In general they contained a hetero atom (phosphorus, halogen, sulfur) incorporated into an organic structure. The trichloroacetoxy functional group in an organometallic structure gave compounds with very high extreme pressure (EP) weld points. Although no pattern has been established for antiwear additives, several additives were found that reduced wear. These were not limited to one chemical class. Some additives gave good EP weld points and also reduced wear, but no one compound was extremely effective in both areas. Contributed by th...