Effect of bulk density: compared to lower-density products, high-density refractory bricks generally exhibit lower values of which service property?

Introduction / Context:
Refractory selection involves trade-offs among density, strength, conductivity, and thermal-shock behavior. High bulk density typically improves strength and reduces open porosity, but it can impair resistance to thermal shock (spalling) because thermal stresses rise with higher elastic modulus and expansion acting over lower compliance.

Given Data / Assumptions:

• Comparing bricks within a similar composition family.
• Service involves thermal cycling or temperature gradients.
• All other factors equal (microstructure aside).

Concept / Approach:
Thermal-shock resistance tends to improve with lower modulus, higher porosity (to blunt crack tips), and lower thermal expansion; higher density often means fewer pores and higher stiffness, which elevates thermal stresses for a given temperature swing, leading to lower spalling resistance. Conversely, high density often boosts slag resistance and strength by reducing permeability.

Step-by-Step Solution:
Link density ↑ → porosity ↓ and modulus ↑.Higher modulus + similar expansion → larger thermal stresses.Hence thermal-shock/spalling resistance generally ↓.Select “Spalling resistance” as the property that tends to be lower.

Verification / Alternative check:
Design charts relating thermal-shock parameter (R or R′) to modulus/strength/conductivity show why denser, stiffer products often fare worse in rapid cycling.

Why Other Options Are Wrong:

• Thermal conductivity: often increases with density (not lower).
• Fusion point: mostly composition-controlled.
• Slag penetration resistance: typically improves with density/low porosity.
• Hot strength: denser products often stronger.

Common Pitfalls:
Assuming “denser is always better”—it depends on the failure mode; for thermal shock, compliance helps.

Final Answer:
Spalling resistance (thermal-shock resistance)