Definition check: in refractory engineering, “spalling” refers to which failure phenomenon?

Introduction / Context:
Spalling is a major cause of premature refractory failure, especially in units that cycle frequently or face steep temperature gradients. Correctly defining spalling helps diagnose root causes and choose preventive measures.

Given Data / Assumptions:

• Thermal cycling or local hot spots are present.
• Material exhibits cracking, flaking, or shelling.
• Definition sought, not a test method.

Concept / Approach:
Spalling is the cracking and detachment of surface layers caused by thermal stresses arising from non-uniform expansion or sudden temperature changes. It is distinct from softening, chemical corrosion, or creep. Materials with low thermal expansion, controlled porosity, and microcrack networks resist spalling better.

Step-by-Step Solution:
Relate thermal gradients to internal stresses.Connect stresses to crack initiation at flaws/pores.Define the observed outcome: flaking/fracture of the hot face.

Verification / Alternative check:
Thermal shock tests (quench cycling) quantify spalling resistance and correlate with service outcomes.

Why Other Options Are Wrong:
Softening is a separate rheological response.Load resistance and chemical resistance are different property domains.

Common Pitfalls:
Equating any crack with chemical attack; spalling is a mechanical/thermal phenomenon.

Final Answer:
Fracture or flaking due to uneven expansion at high temperature (thermal shock)