Silica content for coke-oven silica bricks: the typical SiO2 percentage in silica refractories used for coke-oven walls is approximately what value?

Introduction / Context:
Coke-oven walls operate at high temperatures and require bricks with excellent creep resistance and volume stability. Silica bricks, made with high-purity quartzites, are standard for this duty. Their performance depends strongly on the SiO2 content and mineralogical transformations during service.

Given Data / Assumptions:

• We refer to silica bricks specifically for coke-oven walls.
• Typical industry specifications demand very high SiO2 content.

Concept / Approach:
High-purity silica bricks for coke-oven applications commonly exceed 94–96% SiO2. Such purity ensures desirable transformation behavior and minimal deleterious impurities that could lower softening temperature or increase creep. Therefore, the representative value among the options is about 95%.

Step-by-Step Solution:

Verification / Alternative check:
Vendor specifications and coke-oven design manuals list SiO2 typically ≥ 94–96% with low alkali and alumina impurities, supporting the 95% benchmark.

Why Other Options Are Wrong:

• 45–80%: too low for coke-oven grade silica bricks; such compositions align more with fireclay or mixed aluminosilicates.
• 60–70%: mid-range aluminosilicates, not high-purity silica.

Common Pitfalls:
Confusing “silica brick” with generic “silicate” materials; overlooking that small impurity levels can drastically affect creep and spalling resistance in cyclic service.

Final Answer:
95%