Carbon (graphite) refractories: which statement correctly characterizes their behavior in metallurgical service?

Introduction / Context:
Carbon refractories—graphite blocks, carbon bricks, and carbon-based ramming masses—are ubiquitous in metallurgical vessels (blast furnaces, ladles, aluminum cells) due to their unique combination of properties. Correctly identifying what is true about them helps avoid costly material selection errors.

Given Data / Assumptions:

• Service often includes contact with liquid metals and slags at high temperatures.
• Ambient air may be present unless protected by inert or reducing atmospheres.
• Thermal and electrical transport properties of carbon are high compared with oxide ceramics.

Concept / Approach:
Carbon is generally not wetted by many molten metals and slags, which reduces chemical attack and penetration. This non-wetting characteristic, combined with high thermal conductivity and excellent thermal-shock resistance, explains its use in harsh, cyclic environments. However, carbon does oxidize in air at elevated temperatures; therefore, it requires protection from oxygen (e.g., by coatings or reducing atmospheres). It also does not exhibit low thermal/electrical conductivity—quite the opposite.

Step-by-Step Solution:
Evaluate each statement versus known properties.Confirm the true statement: poor wettability by slags/metals → reduced attack → correct.Mark false claims: “no oxidation,” “poor thermal-shock resistance,” and “extremely low conductivities.”Exclude storage myths: humid storage is not a requirement and may be harmful.

Verification / Alternative check:
Metallurgical literature documents carbon linings’ resistance to slag wetting and their need for oxidation protection (e.g., alumina coatings, controlled atmospheres), validating the chosen statement.

Why Other Options Are Wrong:
(a) False: carbon oxidizes in air at high temperature.(c) False: carbon exhibits excellent thermal-shock resistance.(d) False: carbon has high thermal/electrical conductivity.(e) False: no humid-storage requirement; moisture can cause issues.

Common Pitfalls:
Overlooking oxidation risk in air, leading to premature lining loss.Confusing non-wetting behavior with universal chemical inertness; some slags can still react under certain conditions.

Final Answer:
They are not attacked by many slags because carbon is poorly wetted by most molten metals and slags.