Ceramic bearings for vacuum condition

In the vacuum of space, outgassing materials condense on optical components such as lenses, solar cells and navigation sensors. In the semiconductor industry, contamination from material outgassing can damage multi-million dollar wafers.

Bearing components of interest in a vacuum environment are cages and lubricants. Bearings used in these environments must be ultra clean. Surfaces must be cleaned with solvents and in some cases baked to remove volatile residues that can outgas.

Lubrication: Proper lubrication is critical to extending bearing life. For rolling bearings, oil and grease lubricants are most effective, especially at critical speeds and above where a film of the carrier fluid is formed. In addition to damaging nearby components, degassing can reduce the effectiveness of oil or grease. Fortunately, lubricant technology has evolved and low outgassing and low vapor pressure oils and greases have been developed. These lubricants are usually produced using base oils such as synthetic hydrocarbons or PFPE. The vapor pressure of these fluids at 25°C is about 4.7 × 10 to 12 torr.

The degassing rate increases at higher temperatures due to increased vapor pressure and chemical reaction rate. Therefore, in a vacuum environment, solid lubricants may be required at higher temperatures. Typical solid lubricants for vacuum applications include gold, silver, molybdenum disulfide (MoS2) and polytetrafluoroethylene (PTFE).