Question

Why is graphite a lubricant, and diamond is not?

Answer 1

Hint: Allotropy is the property of an element that allows it to exist in multiple physical states. Carbon is one of the few elements that can have different allotropic forms due to its capacity to have variable oxidation states or coordination numbers. Diamond, graphite, and fullerene are the three allotropes of carbon that we have learned about. Because of their diverse structures, they have varied properties.

Complete answer:
Graphite is used as a lubricant in fast-moving elements of equipment because of its softness and non-volatility. It's used to lubricate equipment parts that operate at high temperatures. Diamond, on the other hand, is a very hard substance and so cannot be used as a lubricant.
Graphite and diamond both have strong $C - C$.These bonds are seen in three dimensions in diamond. These bonds are only found in two dimensions in graphite. Weak bonds hold the individual layers together, allowing them to move over one another and provide lubrication. The carbon-carbon bonds in diamond, on the other hand, are permanently fixed, giving it great hardness and high melting temperatures.

Note:
It is important to keep in mind that graphite is more thermodynamically stable than diamond. Despite the fact that diamond to graphite conversion is thermodynamically advantageous, it does not occur due to high activation energy requirements. The reverse process (graphite to diamond) is thermodynamically unfavourable, although it can be carried out at a pressure of \[50,000 - 60,000{\text{ }}atm\] and a temperature of \[1873K\].