Volatility and Wear Characteristics of a Variety of Liquid Lubricants for Space Applications

Abstract

The vapor pressures and wear characteristics are critical properties for liquid lubricants to assure long-term reliability and performance in space applications. Vapor pressures, obtained using a Knudsen cell technique, and wear properties, obtained using a vacuum four-ball apparatus, were measured for a series of unformulated liquid lubricants. These included: two multiply alkylated cyclopentanes (MACs) (X-1000 and X-2000), two linear perfluoropolyalkylethers (PFPAEs) (Z-25 and 815Z), and four silahydrocarbons (a tri-, a tetra- and two pentas). Vapor pressures were measured at three elevated temperatures (423, 448 and 498K) and extrapolated to room temperature 298K. The lowest 298K vapor pressure of 5.7 × 10−10 Pa, was obtained with the PFPAE fluid (815Z) and the highest value with the low molecular weight MAC (X-1000) at 3.6 × 10−7 Pa. In addition, vacuum wear rates were determined for some of the lubricants. The lowest wear rates (approximately 3 × 10−11 mm3 lmm) were observed for three of the silahydrocarbons while the highest wear rates (approximately 2 × 10−9 mm3 lmm) were observed with the two PFPAE fluids (Z-25 and 815Z). The MAC (X-2000) yielded a wear rate of about 10−10 mm lmm. The results indicated that the silahydrocarbon class of liquid lubricants offers the better potential for space applications. Presented at the 55th Annual Meeting Nashville, Tennessee May 7–11, 2000