is a lubricant additive
that prevents sliding metal surfaces from seizing under conditions of
extreme pressure (EP). At the high local temperatures associated with
metal-to-metal contact, an EP additive combines chemically with the
metal to form a surface film that prevents the welding of opposing
asperities, and the consequent
scoring that is destructive to sliding surfaces
under high loads. Reactive compounds of sulfur,
chlorine, or phosphorus are used to form these inorganic films.