Purpose of firing refractory bricks in manufacture: Why are refractory bricks fired after drying during manufacturing? Choose the most comprehensive reason.

Introduction / Context:
Refractory bricks are manufactured by mixing, shaping, drying, and firing. Firing is not merely to remove moisture; it is a critical step that transforms the raw mix into a strong, stable ceramic capable of high-temperature service.

Given Data / Assumptions:

• The brick has already been dried to remove free water.
• Firing temperatures are sufficient to promote phase development and sintering.
• We require the overall purpose of firing, not a single narrow effect.

Concept / Approach:
Firing performs three key roles: final removal of chemically bound water and organics, development of stable crystalline phases appropriate to the formulation (e.g., mullite in alumino-silicates), and sintering to create ceramic bonds between grains. These processes yield mechanical strength, thermal stability, and resistance to slag and spalling.

Step-by-Step Solution:
Consider dehydration: firing expels residual bound water and burn-out of binders.Consider phase development: temperature drives reactions to produce stable high-temperature minerals.Consider bonding: sintering creates ceramic necks/bonds, enhancing crushing strength and durability.Therefore, the comprehensive choice is “All (a), (b) and (c)”.

Verification / Alternative check:
Standard refractory processing texts describe these combined outcomes of firing, which are essential for service performance.

Why Other Options Are Wrong:
Each of (a), (b), and (c) alone is incomplete; the firing step achieves all simultaneously.

Common Pitfalls:

• Equating “firing” with “drying”; drying occurs earlier at much lower temperatures.
• Ignoring sintering’s impact on mechanical strength and permeability.

Final Answer:
All (a), (b) and (c)