Magnesite (MgO) refractories: which service limitation is typically the most critical—especially for cyclic or abrasive duties in steelmaking and cement/lime plants?

Introduction / Context:
Magnesite (MgO) refractories are classic basic bricks valued for their chemical compatibility with basic slags. However, not all properties are equally strong. This question asks you to identify the typical weak points that limit magnesite brick life in high-temperature furnaces and kilns.

Given Data / Assumptions:

• Base composition is MgO-rich brick.
• Service involves hot abrasion and thermal cycling.
• Basic slag compatibility is generally good for MgO.

Concept / Approach:
While magnesite excels against basic slags, it is comparatively vulnerable to rapid temperature swings (thermal shock) and to mechanical wear by dust-laden, high-velocity flows. Both mechanisms—thermal spalling and abrasion—commonly shorten lining life in rotary kilns, tundish covers, and steelmaking vessels where temperature fluctuations and scouring are significant.

Step-by-Step Solution:
Rule out chemical mismatch with basic slags: MgO is the preferred basic refractory.Identify thermal shock as a known limitation for many dense basic bricks.Add abrasion/erosion as a second frequent failure mode in high-gas-speed or particle-laden streams.Conclude that both thermal shock and abrasion are critical limitations.

Verification / Alternative check:
Field failure analyses and vendor datasheets often cite spalling and erosion as leading causes of MgO brick replacement in cyclic or abrasive services.

Why Other Options Are Wrong:
Attack by basic slag: MgO is resistant; not the primary weakness.Oxidation by air at low temperature: not a typical limiting factor for MgO bricks.

Common Pitfalls:
Assuming chemical compatibility alone guarantees long life; mechanical and thermal shock factors are equally decisive.

Final Answer:
Both (b) and (c)