Among the following refractory brick types, which one contains the minimum percentage of silica (SiO2)? Choose the material that is lowest in SiO2 by typical composition ranges used in industry.

Introduction / Context:
This question checks basic materials knowledge for refractories by asking which listed brick type has the lowest percentage of silica (SiO2). Recognizing typical composition bands helps in selecting the right lining against acid/basic slags, thermal shock, and structural demands.

Given Data / Assumptions:

• “Firebrick” refers to standard fireclay bricks, commonly ~50–60% SiO2.
• “Semi-silica” contains substantial SiO2, though less than pure silica bricks.
• Sillimanite (Al2SiO5) transforms to mullite + silica; still SiO2-bearing.
• Aluminous firebrick (high-alumina brick) has elevated Al2O3 and comparatively lower SiO2.

Concept / Approach:
Among the choices, aluminous (high-alumina) firebricks are formulated to raise Al2O3 (often >45% and up to 90%+ in special grades) while reducing SiO2. Fireclay and semi-silica products contain significantly more SiO2. Sillimanite-based bricks also generate mullite but still originate from an alumino-silicate feed with notable silica content.

Step-by-Step Solution:
List typical SiO2 levels: silica > semi-silica > fireclay ≫ high-alumina.Identify that aluminous firebrick minimizes SiO2 by design.Select the option with the lowest silica fraction: aluminous firebrick.

Verification / Alternative check:
Supplier datasheets consistently show SiO2 lowest in high-alumina refractories compared with fireclay or semi-silica grades.

Why Other Options Are Wrong:
Firebrick: typically ~50–60% SiO2.Sillimanite/Semi-silica: inherently silica-rich relative to high-alumina.High-silica brick: intentionally high SiO2.

Common Pitfalls:
Confusing “acid” vs “basic” classification with absolute silica content; the lowest SiO2 here is the high-alumina choice.

Final Answer:
Aluminous firebrick