Chemical resistance of magnesite bricks: they exhibit poor resistance when attacked by which type of slag?

Introduction / Context:
Refractory selection hinges on matching brick chemistry to slag chemistry. Basic bricks like magnesite perform best against basic slags, but not against acidic ones. The question asks you to identify the mismatch scenario for MgO bricks.

Given Data / Assumptions:

• Magnesite bricks are MgO-rich (basic).
• Acid slags are rich in SiO2.
• Chemical dissolution is the failure mechanism of interest.

Concept / Approach:
In contact with acid slags, MgO can form low-melting silicates, accelerating wear. Conversely, with basic, CaO-rich slags, MgO is compatible and used intentionally. Therefore, magnesite’s poor resistance is to acid (silica-rich) slags.

Step-by-Step Solution:
Classify slag: acid vs basic.Match brick chemistry: MgO is basic; compatible with basic slag, incompatible with acid slag.Select “Acid slag (silica-rich).”

Verification / Alternative check:
Steelmaking practice uses MgO where slags are basic, avoiding acid environments.

Why Other Options Are Wrong:
Basic/lime slags: usual application for MgO bricks.Neutral phosphate only/None: do not reflect standard compatibility.

Common Pitfalls:
Overlooking that slag chemistry dominates refractory corrosion behavior.

Final Answer:
Acid slag (silica-rich)