Vacuum Tribology—Present Status and Challenges

Present status and challenges in vacuum tribology are briefly reviewed. For vacuum applications, lubricats which have low vapor pressure and good tribological performance are required. Solid lubricants have beeen widely adopted for vacuum applications due to their low vapor pressure. One big drawback of solid lubrication is limited life. To achieve long life, a method to supply lubricant during operation is desired. Synthetic liquid lubricants having low vapor pressure have been also used in vacuum due to its better tribological performance than solid lubricant. However, operational temperature of liquid lubricants is limited: liquid lubricants freeze at low temperature, and outgassing and/or vaporization become noticeable at high temperatures. Outgassing from the lubricants causes not only lubricant loss but also contamination of vacuum sysytem. The future challenges in vacuum tribology include lubricant supply system during operation, solid lubricant which can be used both in vacuum and humid air, new liquid lubricant with lower vapor pressure, and low vapor pressure additives for liquid lubricant.