In high temperature furnaces and kilns, refractory bricks are mainly used for which purpose?

Introduction / Context:
Refractory bricks are special construction materials that can withstand very high temperatures without melting or losing strength. This question tests your understanding of why these bricks are used to line furnaces, kilns, and fireplaces, especially in metallurgy and industrial heating processes. Knowing their main purpose helps you connect basic physics of heat flow with practical engineering design.

Given Data / Assumptions:

• Refractory bricks are installed in high temperature furnaces and kilns.
• They have high melting points and low thermal conductivity compared with ordinary bricks.
• The question asks for the main purpose of using them in furnace walls.

Concept / Approach:
The key idea is heat transfer. In a furnace, we want the inside to reach and maintain very high temperatures, while the outer structure and surroundings should not overheat. Materials that conduct heat easily allow heat to escape, wasting fuel and making the outside dangerously hot. Refractory bricks are designed to resist heat and to act as insulators. Their low thermal conductivity slows the flow of heat from the hot interior to the cooler outside, reducing heat loss and improving fuel efficiency. Although some refractories also reflect radiant heat back into the chamber, the primary design goal in most basic questions is to decrease heat flow through the walls, thereby conserving energy and protecting the structure.

Step-by-Step Solution:

Verification / Alternative check:
Engineering references on furnace design describe refractory linings as thermal barriers that protect metal shells and reduce fuel consumption. They emphasise properties such as high refractoriness, chemical stability, and low thermal conductivity. The design objective is to keep the working chamber hot while the outer surface remains much cooler. This confirms that the dominant purpose is insulation and reduction of heat flow, not increasing heat transfer. Therefore option B agrees with standard textbook explanations of refractory brick use.

Why Other Options Are Wrong:

To increase the rate of heat flow so that the furnace walls become hotter is wrong because engineers try to minimise heat loss through walls, not increase it.

To provide a decorative outer finish without affecting heat transfer is incorrect because refractory bricks are chosen for functional thermal properties, not for decoration.

To conduct electricity from heating elements is wrong because refractory materials are usually electrical insulators, not conductors.

Common Pitfalls:
Students sometimes assume that any material used near a heat source must be there to spread heat more effectively. In reality, refractories serve mainly to contain heat, not to distribute it outward. Another mistake is to focus only on the high melting point and forget that low thermal conductivity is equally important. Remember: in furnaces, refractory bricks are used to conserve energy and protect structural components by decreasing heat flow and reducing heat loss through the furnace walls.