Carbon refractories: which statement about carbon (graphite) refractory blocks is correct in typical ironmaking service?

Introduction / Context:
Carbon and graphite refractories have unique properties: very high thermal conductivity, excellent thermal-shock resistance, and chemical inertness in reducing atmospheres. They are widely used in areas like blast-furnace hearths where erosion by hot metal occurs and resistance to wetting by iron is beneficial.

Given Data / Assumptions:

• Molten iron contact, high temperatures, reducing conditions in the hearth.
• Carbon blocks may be impregnated (e.g., with pitch) to reduce permeability.
• Acid/base classification in refractories refers to oxide chemistry, which does not directly apply to carbon.

Concept / Approach:
Molten iron does not readily wet graphite; this helps minimize metal penetration. Carbon refractories are often termed “neutral” because they are not oxides and do not fit classical acid/base slag classifications. Their excellent thermal-shock resistance and high conductivity make them ideal for hearths where thermal gradients and metal contact are severe.

Step-by-Step Solution:
Evaluate wetting: graphite is generally non-wetted by molten iron—so (a) is false.Assess application: carbon blocks line blast-furnace hearths—(b) is true.Check acidity: carbon is not an acidic oxide refractory—(c) is false.Hence, only statement (b) is correct.

Verification / Alternative check:
Ironmaking texts specify carbon/graphite hearth linings to reduce hot-metal/slag attack and enhance campaign life, confirming (b).

Why Other Options Are Wrong:

• (a) Opposite of practice; non-wetting is a key advantage.
• (c) Misclassification; carbon is considered neutral.
• (d) Aggregates false statements.
• (e) Describes basic CaO-based refractories, not carbon blocks.

Common Pitfalls:
Applying oxide acidity/basicity labels to carbon; assuming metals always wet carbon surfaces.

Final Answer:
They are used in the hearth of blast furnaces