Atmosphere compatibility: which refractory brick type should NOT be used in an oxidising atmosphere because it degrades by oxidation?

Introduction / Context:Furnace atmospheres can be oxidising, neutral, or reducing. Refractory selection must consider chemical stability under the prevailing oxygen potential. Carbon-containing bricks excel in reducing or neutral conditions but will react unfavourably when exposed to oxygen at high temperature.

Given Data / Assumptions:

• Candidates include tar-bonded dolomite (contains carbon binder), carbon bricks, silica bricks, and fireclay bricks.
• Oxidising atmosphere implies significant O2 or oxidising species present.
• Service temperatures are high enough to promote rapid oxidation reactions.

Concept / Approach:Carbon bricks and carbon-rich linings oxidise to gaseous CO/CO2 in the presence of oxygen, causing rapid mass loss, porosity increase, and structural failure. While tar-bonded dolomite contains carbon in the binder, the most clearly unsuitable category in a strongly oxidising zone is pure carbon brick. Silica and fireclay are stable in oxidising conditions, though each has its own limits regarding thermal shock and slag chemistry.

Step-by-Step Solution:Identify oxidation-prone composition: carbon bricks.Relate oxidation to weight loss and strength loss.Conclude that carbon bricks should not be used in oxidising atmospheres.

Verification / Alternative check:Industrial practice restricts carbon-containing refractories to reducing zones (blast furnace hearths, ladles with protective slag/cover, certain non-ferrous operations).

Why Other Options Are Wrong:Tar dolomite: some oxidation sensitivity exists, but the question targets the clearly unsuitable class—carbon bricks.Silica/Fireclay: acceptable in oxidising atmospheres within their temperature/slag limits.

Common Pitfalls:Equating any presence of carbon binder with pure carbon bricks; not differentiating between mild and strongly oxidising conditions.

Final Answer:Carbon