Fireclay (alumino-silicate) refractories: which combined statement correctly summarizes their behavior toward basic slags, salts/bases, and dimensional change on firing?

Introduction / Context:
Fireclay bricks are widely used due to their cost-effectiveness and balanced performance, yet their chemical compatibility has limits. Understanding interaction with slags, salts, and bases is essential for correct placement in furnaces and kilns.

Given Data / Assumptions:

• Fireclay refractories are silica–alumina materials with moderate Al2O3.
• Basic slags are CaO-rich; acidic slags are SiO2-rich.
• Firing induces densification and typical linear shrinkage.

Concept / Approach:
Fireclay withstands acidic environments better than basic. In basic slags (or with lime/magnesia), reactions form low-melting aluminates/silicates, reducing service life. Salts such as chlorides and sulphates can flux and form fusible phases. During manufacturing firing, sintering densifies the body and produces measurable shrinkage; excessive shrinkage is controlled by formulation and firing schedule.

Step-by-Step Solution:
Assess slag compatibility: basic slags attack fireclay → statement (a) is correct.Consider chemical reactivity: salts/bases can form fusible compounds → (b) is correct.Evaluate firing behavior: densification causes shrinkage → (c) is correct.Therefore the combined choice (d) is correct.

Verification / Alternative check:
Placement guides recommend fireclay for acidic zones and warn against basic slag exposure; standard shrinkage-on-firing data are reported in product datasheets.

Why Other Options Are Wrong:
Single statements (a), (b), (c) are each true but incomplete.None of the above contradicts well-known behavior.

Common Pitfalls:
Using fireclay in CaO-rich environments; mixing up firing shrinkage with thermal expansion in service.

Final Answer:
All of the above: (a), (b) and (c)