Q1: Which of the following is not a suitable solid lubricant ?

ANS:D - None of these

1. Talc: Talc is a naturally occurring mineral composed of hydrated magnesium silicate. It is known for its softness and lubricating properties. Talc has a layered structure similar to graphite, which allows for some reduction in friction when used as a lubricant. However, talc is not as effective as other solid lubricants like graphite and molybdenum disulfide. It is commonly used in applications where a low level of lubrication is sufficient, such as in talcum powder, cosmetics, and as a filler material in various products.
2. Molybdenum disulfide: Molybdenum disulfide (MoS2) is a solid lubricant widely used in various industrial applications. It consists of layers of molybdenum atoms sandwiched between layers of sulfur atoms. These layers can slide over each other with minimal resistance, providing excellent lubricating properties even under high temperatures and pressures. Molybdenum disulfide is used in applications where extreme conditions require high-performance lubrication, such as in automotive components, aerospace equipment, and industrial machinery.
3. Graphite: Graphite is another commonly used solid lubricant with a layered crystal structure similar to molybdenum disulfide. It consists of carbon atoms arranged in tightly packed layers that can slide over each other easily, resulting in low friction and excellent lubricating properties. Graphite exhibits good lubrication even at high temperatures and in harsh environments. It is widely used in various industrial applications, including as a lubricant for machinery, locks, bearings, and electrical contacts.

In summary, while all three materials have lubricating properties to some extent, talc is generally considered to be less effective compared to molybdenum disulfide and graphite, especially in demanding industrial applications requiring high-performance lubrication. Molybdenum disulfide and graphite are preferred choices for such applications due to their superior lubricating properties and stability under extreme conditions.