---
title: "Solid lubricants and their use"
subject: "Engineering Chemistry"
chapter: 8
key: "semester_2/engineering_chemistry:solid-lubricants"
source: https://www.bctengineer.com/q/semester_2/engineering_chemistry/solid-lubricants
site: BCT Engineering
---

# Solid lubricants and their use

Engineering Chemistry · Chapter 8: Lubricants and Paints

- Asked in: 2073 Magh, 2 marks; 2070 Magh, 2 marks (asked 2 times)
- Video: [Solid Lubricant - Lubricants - Engineering Chemistry 1](https://www.youtube.com/watch?v=mzgsKCDCh4k) — Ekeeda
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_2/engineering_chemistry/solid-lubricants
- Whole chapter: https://www.bctengineer.com/md/semester_2/engineering_chemistry/chapter-8

## Question

What are solid lubricants? Under what condition, they are used.

## Short answer

Solid lubricants like graphite and MoS₂ have layered structures that shear easily. They are used at very high temperatures, under extreme loads and slow speeds, in vacuum, or where oil would contaminate products or collect dust.

## Answer

**Solid lubricants** are solids with a layered structure that slide easily over each other, such as graphite, molybdenum disulfide (MoS₂), talc and soapstone. They are used where oils and greases fail:
- at very high temperatures (graphite up to about 450 °C in air) where oil burns or evaporates;
- under extremely heavy loads and very slow speeds where an oil film would be squeezed out;
- in vacuum or at very low temperature;
- where oil would contaminate the product (food, textile, paper machines) or collect dust;
- as an additive or dry film on parts that cannot be lubricated often.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. Why do solid lubricants such as graphite and MoS2 reduce friction?
   A. Their layered structure lets layers slide over each other
   B. They melt to form a fluid film
   C. They react chemically with the metal
   D. They evaporate and cool the surface
   Answer: A. Solid lubricants have layers that slide easily over each other. (Key point: Why solids lubricate)

2. Why is graphite preferred to oil at very high temperature?
   A. Graphite becomes liquid at high temperature
   B. Oil becomes harder at high temperature
   C. Oil burns or evaporates, while graphite stays effective up to about 450 °C
   D. Graphite has lower melting point than oil
   Answer: C. Oil burns or evaporates at high temperature; graphite works up to about 450 °C in air. (Key point: High temperature)

3. In which situation is a solid lubricant the best choice?
   A. Where oil would contaminate the product, such as in food or textile machines
   B. Where machines run at high speed with light load
   C. Where frequent oil changes are easy
   D. Where a liquid film is needed to carry away heat
   Answer: A. Solid lubricants are used where oil would contaminate (food, textile, paper), in vacuum, at heavy loads and very high temperature. (Key point: Conditions of use)

## Related in Engineering Chemistry

- [Lubricant functions; solid lubricants](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Alubricant-functions-solid) — Engineering Chemistry, chapter 8
- [Lubricants and their classification](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Alubricants-classification) — Engineering Chemistry, chapter 8
- [Lubricant functions; grease and solid lubricant use](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Alubricant-functions-grease-solid) — Engineering Chemistry, chapter 8

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