Semi-silica bricks compared with silica bricks: which statements about fusion point and thermal-shock (spalling) resistance are correct?

Introduction / Context:
Semi-silica bricks are engineered to balance refractoriness with improved shock resistance compared with high-silica bricks. This question tests recognition of those trade-offs.

Given Data / Assumptions:

• Silica bricks have very high refractoriness but poor shock resistance.
• Semi-silica incorporates more alumina-bearing phases (e.g., mullite) improving spalling resistance.

Concept / Approach:
As alumina increases relative to pure silica, softening temperature can reduce slightly (lower fusion point than pure silica). However, shock resistance typically improves, giving semi-silica an advantage in cycled environments.

Step-by-Step Solution:
Compare fusion points: semi-silica < silica.Compare shock resistance: semi-silica > silica.Select “Both (a) and (b).”

Verification / Alternative check:
Material datasheets show semi-silica with better thermal shock indices than silica bricks.

Why Other Options Are Wrong:
“Neither” contradicts well-known property trends.

Common Pitfalls:
Equating highest refractoriness with best all-around performance; cyclic service needs shock resistance.

Final Answer:
Both (a) and (b)