Chrome–magnesite bricks: which statement is reliably true for this class compared with silica bricks when considering performance at high temperature under load?

Introduction / Context:
Chrome–magnesite (magnesia–chrome family) refractories are widely used in steelmaking and other basic environments. Two key selection metrics are refractoriness under load (RUL) and softening behavior at temperature. The question asks for a correct general statement compared with silica bricks.

Given Data / Assumptions:

• Silica bricks show excellent PCE but comparatively lower RUL because of viscous deformation near service temperatures.
• Magnesia-containing bricks generally demonstrate superior RUL at high temperature under load.
• Nomenclature distinctions (chrome–magnesite vs. magnesite–chrome) depend on relative chromite/magnesia percentages and vary by source.

Concept / Approach:
RUL gauges the ability to bear load at elevated temperature without excessive deformation. Magnesia–chrome compositions typically exhibit higher RUL than silica bricks because periclase-containing matrices retain rigidity and creep resistance at high temperatures. Therefore, the most reliable comparison among the choices is that chrome–magnesite bricks have higher RUL than silica bricks.

Step-by-Step Solution:
Compare high-temperature load-bearing behavior of silica vs. magnesia–chrome.Note silica’s good PCE but relatively poorer RUL.Conclude that chrome–magnesite → higher RUL than silica.

Verification / Alternative check:
Textbook tables of RUL values place magnesia–chrome and high-alumina bricks above silica bricks for load-bearing at high temperature.

Why Other Options Are Wrong:
Acidic in nature: chrome–magnesite is commonly classed as basic or near-neutral, not acidic.Neutral in nature: classification varies with composition; “always neutral” is too absolute.Made by 30% chromite and 70% periclase: a specific mix describes a magnesite–chrome variant; not a universal definition for “chrome–magnesite.”Lower softening point than fireclay bricks: generally incorrect; magnesia–chrome withstands higher temperatures.

Common Pitfalls:
Confusing PCE (no load) with RUL (with load).Overgeneralizing chemical classification without considering composition window.

Final Answer:
Having higher RUL than silica bricks