Blast-furnace hearth carbon blocks: which property chiefly helps avoid “skull” formation (adherent frozen metal/slag) when the hearth cools?

Introduction / Context:
Carbon blocks are used in blast-furnace hearths for their chemical compatibility and thermal properties. When the furnace cools, skulls (adherent frozen layers) can form. The question asks which property of carbon blocks helps prevent this adhesion.

Given Data / Assumptions:

• Molten iron/slag contact the hearth lining.
• Cooling may cause solidification at the interface.
• Adhesion depends on wetting behavior.

Concept / Approach:
Non-wetting behavior reduces adhesion of melts to the lining. Carbon exhibits low wettability by molten iron and many slags, so frozen layers detach more readily and are less likely to bond strongly. While high thermal conductivity is beneficial for heat flow and temperature control, it does not by itself ensure non-adherence.

Step-by-Step Solution:
Identify skull formation as an adhesion/wetting issue.Recall carbon’s low wettability to iron/slag.Select non-wetting characteristics as the key property.

Verification / Alternative check:
Operational notes highlight carbon’s non-wetting property as a reason for its use in hearth zones exposed to hot metal.

Why Other Options Are Wrong:
High thermal conductivity/density/low porosity: beneficial for other reasons but not the primary anti-skull mechanism.Electrical resistivity: not directly related.

Common Pitfalls:
Confusing heat flow control with adhesion control; both matter but address different failure modes.

Final Answer:
Non-wetting characteristics toward molten iron/slag