Lubricant Properties and Testing

The term lubricant generally suggests oil or grease simply because they are the most common lubricants in use; but they are not exclusive and, in fact, any fluid can be used as a lubricant in the right circumstances. In modern applications a very wide range of fluids are used as lubricants. Air or gas bearings are now quite common, there are numerous examples of the use of water as a lubricant and there is an increasing use of process fluids, one rather exotic example being the use of liquid sodium as a lubricant in nuclear reactors. In some situations solid lubricants are used but the main emphasis in this chapter is on fluid lubricants.