To reduce thermal-spalling tendency, a refractory should preferably possess which combination of thermal properties?

Introduction / Context:
Thermal spalling arises from steep temperature gradients and differential expansion. Material properties that reduce temperature gradients or strain amplitude improve resistance to cracking and flaking under thermal shock.

Given Data / Assumptions:

• Thermal diffusivity = k / (rho * Cp), where k is conductivity and Cp is specific heat.
• Lower coefficient of thermal expansion reduces stress for a given gradient.

Concept / Approach:
Higher diffusivity spreads heat faster, lowering internal gradients. Lower Cp also increases diffusivity for a given k and density. Low thermal expansion reduces strain per degree of temperature change. Together, these traits decrease the driving forces for spalling.

Step-by-Step Solution:
Target properties that minimize gradients and thermal strain.Recognize diffusivity ↑ and expansion ↓ both help.Select “All (a), (b) and (c).”

Verification / Alternative check:
Thermal shock indices in textbooks correlate improved resistance with lower expansion and higher diffusivity.

Why Other Options Are Wrong:
Single-property answers omit synergistic effects; high porosity alone is not a universal cure.

Common Pitfalls:
Confusing conductivity with diffusivity; diffusivity explicitly includes Cp and density.

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