Mullite Refractory Brick for Blast Furnace, Stoves & Cycled Kiln Zones

Mullite brick is chosen when thermal cycling, not chemical attack, is what destroys the lining. Converting the alumina-silica matrix to mullite gives the brick a markedly lower thermal expansion coefficient than corundum, so it moves less with each temperature swing — and linings that move less, spall less.

Why Expansion Is the Hidden Killer

Every time a furnace heats up and cools down, the lining expands and contracts. If adjacent courses or the brick surface and interior move by different amounts, stress builds, microcracks form, and eventually pieces of the hot face come away. That is spalling, and it ends more ceramic, kiln and cycled-zone campaigns than corrosion does.

Mullite addresses this at the material level. Lower expansion means lower stress per cycle, which means more cycles before cracking. Combined with good hot strength — cold crushing strength ≥80 MPa with RUL to 1700 °C on XZK-ML70-B — the brick holds together in service that would destroy a higher-purity, more brittle material.

Reading the Grades

• XZK-ML70-B — 70% Al₂O₃, Fe₂O₃ ≤0.2%, bulk density 2.65 g/cm³, RUL 1700 °C. The premium pressed grade for high-temperature, cycled, loaded zones and where iron contamination matters.
• XZK-ML70-A — 70% Al₂O₃, Fe₂O₃ ≤1.2%, RUL 1620 °C. General-duty pressed grade.
• XZK-ML65-C — 65% Al₂O₃, cast large block format, RUL 1600 °C. Fewer joints for large flat areas such as kiln car tops.

Where Mullite Sits Relative to Its Neighbours

• vs corundum-mullite — mullite has better cycling behaviour; corundum-mullite resists slag better and is denser. Cycling favours mullite; slag and temperature favour corundum-mullite.
• vs high-alumina — mullite has lower expansion and higher RUL; high-alumina costs less. Use mullite where cycling or load justifies it.
• vs basic refractories — mullite is alumina-based and is attacked by strongly basic slags. For BOF and ladle slag lines, use MgO-C, AMC or spinel grades.

Manufacturing and Documentation

XZK mullite bricks are pressed or cast from controlled alumina-silica raw materials and fired to develop the mullite phase. Bulk density and porosity per ASTM C830, crushing strength per ASTM C133, RUL per ISO 1893 and chemistry per GB/T 6900 are tested per batch, with a Certificate of Analysis on every shipment. Complex shapes for kiln cars, burner surrounds and crowns are produced to drawing with machined faces where required.

Where This Grade Sits in the Lining System

Corundum and high-alumina grades earn their place on hot strength and creep resistance, and those properties only pay back if the surrounding zones survive as long as they do. Putting the strongest brick into the harshest zone and leaving the rest to habit is how most of the refractory budget is actually lost.

XZK supplies mullite brick as one zone of a zoned package rather than as a standalone item: the grades normally zoned alongside it — among them corundum mullite brick — are documented on the corundum and high-alumina refractories page, and the vessel-level architecture — where each zone starts and ends, and which mechanism actually limits the campaign — is set out on the blast furnace and hot blast stove pages.

The MMK Magnitogorsk No.10 BF and 375 t ladle programme reference documents how this class of material performed in full service, with the measured campaign figures rather than datasheet values.