Safe storage of refractories: which refractory product specifically requires a controlled atmosphere (both temperature and humidity) during storage to prevent hydration and deterioration before use?

Introduction / Context:
Refractory materials often contain phases that react unfavorably with atmospheric moisture and carbon dioxide during storage. Some products, especially basic refractories containing free CaO/MgO or special binders, can hydrate, swell, crack, or otherwise degrade if not stored correctly. This question tests recognition of the refractory type that must be stored under controlled temperature and humidity to ensure performance at installation.

Given Data / Assumptions:

• Choices include acidic (fireclay), high-alumina (mullite), and basic refractories (magnesite, dolomite).
• “Controlled atmosphere” implies dry, temperature-stable, and usually covered or sealed storage.
• Primary degradation mechanisms are hydration and oxidation of binders.

Concept / Approach:
Tar-bonded dolomite bricks contain doloma (CaO·MgO) with a tar/pitch binder. Free lime (CaO) and periclase (MgO) are highly reactive to moisture and carbon dioxide (forming hydroxides and carbonates), leading to disruptive volume changes. The tar binder can oxidize if stored hot or in poorly ventilated, humid conditions. Hence, these bricks require strictly controlled storage. By contrast, fireclay and mullite bricks are comparatively stable in ambient conditions, while magnesite bricks also require dry storage but are generally less sensitive than tar-bonded dolomite to humidity and binder oxidation issues.

Step-by-Step Solution:
Identify basic bricks prone to hydration: dolomite (CaO·MgO) and magnesite (MgO).Note binder sensitivity: tar-bonded systems are additionally vulnerable to oxidation and moisture ingress.Infer highest storage sensitivity: tar-bonded dolomite demands controlled humidity and temperature.Select the option that aligns with these risks.

Verification / Alternative check:
Field guidance for steel plants and refractory vendors specifies sealed packaging, desiccants, and temperature limits for tar-bonded dolomite bricks to prevent pre-hydration and loss of strength prior to ramming or laying.

Why Other Options Are Wrong:
Fireclay bricks: relatively inert to ambient humidity; standard dry storage suffices.Mullite bricks: chemically stable alumina–silicate; do not require controlled humidity.Magnesite bricks: need dry storage, but tar-bonded dolomite is more critically sensitive.High-alumina castables: supplied sealed; while moisture control matters, they do not mandate controlled atmosphere like tar-bonded dolomite bricks.

Common Pitfalls:
Assuming all basic bricks need identical storage care; tar-bonded dolomite is the most sensitive.Confusing transport waterproofing with genuine humidity and temperature control.

Final Answer:
Tar-bonded dolomite bricks