A lubricant is an organic substance used to reduce friction between two surfaces that are in contact with each other; it is done by ultimately reducing friction and the heat generated when the two surfaces move.
Gas Lubricants include (Air, Nitrogen, and Helium) that is often used in Gas- lubricated bearings though air is the most commonly employed.
Liquid oil lubrication- where Low viscosity oils have low fluid friction losses and hence results in low heat generation. The liquid can easily carry away heat.
They have high boiling point and Low freezing point also have high resistance to oxidation and wear. They also comes with non-corrosive properties.
Lithium Greases are semi sold lubricants they are black or yellow sticky mass which is used in the bearings for lubrication purpose.
It has unique properties which includes Resistance to water & can withstand harsh conditions, Important additives, Thickener and more.
Graphite, hexagonal boron nitride, molybdenum disulfide and tungsten disulfide are examples of solid lubricants.
Some retain their lubricity to very high temperatures. The use of some such materials is sometimes restricted by their poor resistance to oxidation.