Alumina content comparison: among the listed refractory materials, which typically contains the highest percentage of Al2O3?

Introduction / Context:
Alumina (Al2O3) content is a key indicator of a refractory’s thermal shock resistance, refractoriness, and slag compatibility. Higher Al2O3 generally correlates with improved hot strength and corrosion resistance in acidic or neutral environments. Comparing common materials helps in quick selection for furnace linings and high-temperature equipment.

Given Data / Assumptions:

• Typical compositions: firebrick (≈ 30–45% Al2O3), aluminous (high-alumina) firebrick (≈ 45–60% Al2O3 for the common grades), sillimanite (Al2SiO5, theoretical ≈ 61–62% Al2O3), magnesite (MgO-based, negligible Al2O3), silica brick (high SiO2, trace Al2O3).
• We compare typical grades, not specialty 80–90% alumina or fused-cast products.

Concept / Approach:
Sillimanite (Al2SiO5) naturally provides a high alumina fraction by stoichiometry. Standard “aluminous firebrick” grades increase alumina over fireclay but commonly remain below sillimanite unless explicitly specified as very-high-alumina products. Magnesite and silica bricks are not alumina-rich by design.

Step-by-Step Solution:

Verification / Alternative check:
Handbook tables for standard fireclay, high-alumina bricks, and sillimanite bricks confirm these typical ranges, with sillimanite often topping basic catalogued alumina contents among these options.

Why Other Options Are Wrong:

• Firebrick: moderate Al2O3; lower than sillimanite.
• Aluminous firebrick: higher than firebrick but typically not exceeding sillimanite in standard grades.
• Magnesite and silica bricks: not alumina-based.

Common Pitfalls:
Assuming “aluminous” always implies the highest alumina regardless of grade; overlooking that specialty 80–90% alumina bricks exist but are not implied here.

Final Answer:
Sillimanite