Carbon (graphite) refractories: which property combination is characteristically very high, explaining their use in high-temperature, reducing atmospheres and in zones needing rapid heat flow?

Introduction / Context:
Carbon refractories (graphite and carbon blocks) are widely used in ironmaking and steelmaking where reducing atmospheres and contact with slags or molten metal demand exceptional thermal and chemical performance. This question asks which property combination is characteristically very high and central to their industrial usefulness.

Given Data / Assumptions:

• Service occurs at high temperature in largely reducing conditions (limited oxygen).
• Candidate properties include refractoriness (resistance to softening), thermal conductivity, wetting, and porosity.
• We focus on intrinsic material behavior of dense carbon/graphite bricks and blocks.

Concept / Approach:
Graphite has an exceptionally high sublimation temperature and maintains strength at elevated temperatures in low-oxygen environments, which translates to very high refractoriness in service. Simultaneously, carbon and graphite possess high thermal conductivity, enabling rapid heat flow and temperature equalization that can reduce local thermal gradients. These two properties—refractoriness and thermal conductivity—together explain why carbon linings are selected for hearths, tap holes, and other hot-face regions under reducing conditions.

Step-by-Step Solution:
Identify the properties that control performance in reducing atmospheres.Recall that carbon/graphite resists softening up to extremely high temperatures → high refractoriness.Recall that graphite conducts heat very effectively → high thermal conductivity.Combine findings → the correct choice is both high refractoriness and high thermal conductivity.

Verification / Alternative check:
Industrial data sheets for carbon blocks show very high thermal conductivity (relative to oxide refractories) and excellent hot strength when oxygen is limited. Field applications (blast furnace hearths, ladle bottoms in specific designs) corroborate these traits.

Why Other Options Are Wrong:
Wetting characteristics: carbon is often selected because many slags and metals wet it poorly; “very high wetting” is not a desirable trait.Porosity: can be tailored, but “very high porosity” is not characteristic of dense carbon blocks.

Common Pitfalls:
Assuming carbon is suitable in oxidizing atmospheres; oxidation rapidly damages carbon.Confusing electrical conductivity (also high) with thermal conductivity; both are high for graphite, but the question emphasizes thermal performance.

Final Answer:
Both (b) and (c)