Hot metal mixer (upper portion) linings: mullite bricks are selected primarily to resist which service actions?

Introduction / Context:
Hot metal mixers store and homogenize molten iron before steelmaking. The upper lining faces combined mechanical washing and chemical corrosion. Mullite bricks provide a balanced resistance profile for these challenges.

Given Data / Assumptions:

• The upper portion contacts splashing hot metal and overlying slag.
• Requirements include erosion resistance and chemical corrosion resistance.

Concept / Approach:
Mullite’s alumina-rich composition offers good hot strength and chemical durability against many slags, while microstructure design improves resistance to washing and abrasion. Therefore, mullite linings are chosen to address both dominant degradation modes in the upper mixer regions.

Step-by-Step Solution:
Identify service threats: washing + slag corrosion.Match mullite’s properties to those threats.Conclude that both effects are mitigated by mullite.

Verification / Alternative check:
Plant practice and vendor guidance align mullite with zones subject to combined erosion and corrosion.

Why Other Options Are Wrong:
Choosing only one mechanism underestimates the operational demands.

Common Pitfalls:
Overlooking mechanical erosion when focusing solely on chemical compatibility.

Final Answer:
Both (a) & (b)