Thermal expansion of refractory bricks: up to 1000 °C, which brick type exhibits very low linear thermal expansion (≤ 0.5%)?

Introduction / Context:
Dimensional stability with temperature is critical for tight-tolerance linings and interlocking brickwork. Excessive thermal expansion leads to spalling, joint closure, and structural stress. Knowing typical expansion ranges for common brick chemistries informs design of expansion joints and choice of anchors.

Given Data / Assumptions:

• Temperature reference: up to about 1000 °C.
• We compare common bricks: fireclay, silica, magnesite, and corundum (high-alumina).

Concept / Approach:
Fireclay bricks generally show relatively low linear expansion to 1000 °C, often around 0.4–0.6%, depending on formulation and firing. Silica bricks display higher and more complex expansion due to polymorphic transformations of silica; magnesite bricks exhibit higher expansion typical of basic refractories; corundum (high-Al2O3) expansions are moderate to higher than fireclay in this range. Therefore, among the choices, fireclay provides the lowest expansion up to 1000 °C and fits the ≤ 0.5% criterion frequently cited in handbooks for selected grades.

Step-by-Step Solution:

Verification / Alternative check:
Manufacturer datasheets show fireclay grades with 0.4–0.6% expansion at 1000 °C; silica bricks often exceed 1% with distinct transformation peaks, confirming the selection.

Why Other Options Are Wrong:

• Silica brick: larger expansion and transformation-induced changes.
• Magnesite brick: typically higher expansion than fireclay.
• Corundum brick: may be near or above 0.6–0.8% depending on grade.
• Chrome brick: also higher than fireclay in this range.

Common Pitfalls:
Applying single values universally; actual expansion depends on specific composition, porosity, and firing—always consult datasheets.

Final Answer:
Fireclay brick