Effect of density on silica refractories: as bulk density of silica bricks increases, how do slag-corrosion resistance and thermal spalling resistance change?

Introduction / Context:
Bulk density and porosity are fundamental microstructural parameters controlling how refractories behave in service. For silica bricks used in high-temperature structures, density affects both chemical corrosion by slags and resistance to thermal shock or spalling.

Given Data / Assumptions:

• We compare silica bricks of different bulk densities (implying different porosities).
• Slag attack refers to chemical corrosion and infiltration.
• Spalling resistance refers to the ability to withstand thermal-shock-induced cracking.

Concept / Approach:
Higher bulk density generally means lower open porosity and a more continuous solid network. Lower porosity reduces slag infiltration and dissolutive attack, improving corrosion resistance. However, lower porosity also reduces the ability to accommodate thermal strains and to blunt crack propagation, which can lower thermal-shock/spalling resistance. Conversely, more porous (lower-density) bricks often show better thermal shock tolerance but worse slag resistance due to easier penetration pathways.

Step-by-Step Solution:
Link density ↑ → porosity ↓.Porosity ↓ → fewer infiltration paths → slag resistance ↑.Porosity ↓ → less strain accommodation and crack deflection → spalling resistance ↓.Therefore, both “slag resistance increases” and “spalling resistance reduces” are true as density increases.

Verification / Alternative check:
Property charts for silica bricks show corrosion resistance improving with density, while thermal-shock tests (quench cycles to failure) typically favour more porous grades.

Why Other Options Are Wrong:
Choosing only (a) or only (b) captures half the trend; selecting neither contradicts well-understood porosity effects.

Common Pitfalls:
Assuming “denser is always better” without trade-offs; overlooking that application dictates whether corrosion or thermal shock is the dominant design constraint.

Final Answer:
Both (a) and (b).