Solid lubricants are materials which depsite being in the solid phase, are able to reduce friction between two surfaces sliding against each other without the need for a liquid medium,
The two main solid lubricants are graphite and molybdenum disulphide.
Graphite: It is the most widely used of all solid lubricants.
It is very soapy to touch, non-inflamable and not oxidized in air below 375 °C
In the absence of aor, it can be used upto very much higher temperatures.
Graphite is used either in powdered form or as suspension.
When graphite is dispersed in oil, it is called 'oilddag' and when dispersed in water, it is called 'aquadag'
Molybdenum disulphide:
It posses very low coefficient of friction and is stable in air upto 400 °C
Its fine powder may be sprinkled on surfaces sliding at high velocities, when it fills low spots in metal surfaces, forming its film.