Polysilahydrocarbons as Lubricants for Aerospace Application (269)

Liquid lubricants suitable for successful application in mechanical devices operating in outer space are required to have unique properties. They must have extremely low vapor pressure and at the same time should have low-temperature liquid properties. While increasing molecular weights tends to reduce vapor pressure, it also tends to increase melting point. Thus, a combination of desired properties is not easily achieved. Polysilahydrocarbons have been considered as potential candidates, but it is not easy to obtain them without impurities that are difficult to remove, and which can outgas in the ultra high vacuum of space resulting in contamination of sensitive components onboard a spacecraft.

The University of Dayton Research Institute, in conjunction with the Air Force Materials and Manufacturing Directorate, has developed polysilahydrocarbons that can be obtained without the impurities which can lead to outgassing. While the reactions developed take several days to complete, the products obtained in high purity are high molecular weight materials with excellent low-temperature liquid properties. For instance, a polysilahydrocarbon containing 97 carbon atoms, has a kinematic viscosity of 34,910 cSt. at –40°C, and 15.2 cSt. at 100°C. It has a volatilization onset temperature (T0) of 336°C at 0.24 mm Hg, and the temperature at which half the fluid weight is lost (T1/2) is 350°C at 0.24 mm Hg. In comparison, a currently-used material where the major component contains 65 carbon atoms shows a kinematic viscosity of 77870 cSt. at -40°C, 14.4 cSt. at 100°C, T0 of 278oC and T1/2 of 294°C at 0.24 mm Hg.

The materials developed are suitable for any application requiring a liquid of high molecular weight, low volatility, and good antiwear properties. The properties of these polysilahydrocarbons can be tailored by varying the substituent alkyl groups. The methods of preparation are simple and provide high-purity products in high yield.

U.S. Patent Application 09/385,397 filed August 30, 1999.

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