Service limitation of chrome–magnesite bricks: identify the furnace where chrome–magnesite refractories are generally not preferred due to chemical incompatibility and attack by the molten charge or fluxes.

Introduction / Context:
Chrome–magnesite refractories couple magnesia with chromite phases and perform well with basic steelmaking slags. However, lining selection must consider the specific molten metal environment; certain metals, notably aluminium, can reduce or wet oxide phases and cause rapid degradation.

Given Data / Assumptions:

• Application choices include basic oxygen steelmaking, steel-melting wear zones, and aluminium melting.
• Molten aluminium exhibits strong reducing behavior and problematic wetting with many oxides.
• We prioritize chemical compatibility over mere hot strength.

Concept / Approach:
In steelmaking with basic slags, chrome–magnesite shows good corrosion resistance and structural performance. In contrast, molten aluminium and its fluxes can aggressively attack and penetrate chromite- or magnesia-containing oxides, making chrome–magnesite unsuitable for aluminium melting furnaces. As a result, aluminium practice relies more on alumina-graphite, silicon carbide, and other specially formulated low-wetting linings.

Step-by-Step Solution:
Match refractory chemistry to process chemistry.Recognize aluminium’s reducing/wetting tendencies toward many oxides.Conclude that aluminium melting furnaces are the exception.

Verification / Alternative check:
Industry references for non-ferrous metallurgy list chrome–magnesite as generally unsuitable for molten aluminium contact zones, confirming the choice.

Why Other Options Are Wrong:
LD converter / steel-melting wear zones: common basic applications for chrome–magnesite.“All of them” cannot be true because it works well in (a) and (c).Tundish backup: distractor; practice varies but does not overturn the aluminium exception.

Common Pitfalls:
Assuming good steelmaking performance implies suitability for non-ferrous service.Ignoring metal wetting and reduction reactions in selection.

Final Answer:
Aluminium melting furnaces