What is the difference between corundum bricks and mullite bricks?

How to distinguish between corundum bricks and mullite bricks when selecting bricks for high-temperature kilns? After reading this article, you’ll avoid making mistakes when choosing bricks in the future.

1.Composition and Crystals

Corundum bricks are purer, while mullite bricks are more “composite”.

The former type of brick has an Al₂O₃ content of ≥90%. Its main crystalline phase is corundum, and its crystal structure is dense and uniform.

The Al₂O₃ content of the latter type of brick is generally between 65% and 75%. Its main crystalline phase is mullite, and it contains a small amount of glass phase.

2.Performance Comparison

(1)Refractoriness

Corundum bricks are ≥1800 ℃, and mullite bricks are about 1700 ℃. The temperature difference between the two is about 100 ℃, and corundum is preferred for the ultra-high temperature range.

(2)Thermal shock resistance

Mullite crystals have a low coefficient of thermal expansion and interlocked grains, which can buffer stress.

Corundum refractory bricks have a high coefficient of thermal expansion and are prone to cracking when subjected to rapid cooling or heating.

(3)Resistance to erosion

Corundum bricks have high purity and a lower dissolution rate for high-alkali, high-iron oxide slag than mullite bricks.

However, in an atmosphere containing SiO₂, a mullite protective layer can be re-formed on the surface of mullite bricks, making them even more stable.

(4)Thermal conductivity

The former is around 3.0 W/(m·K), while the latter is around 1.8 W/(m·K). For applications requiring high insulation, the latter is more energy-efficient.

3.Price and Selection

First, lock in the temperature, then calculate the thermal shock, and finally look at the price.

The raw material for corundum bricks is mainly fused white corundum, and the price per ton is about 1.5 to 2 times that of mullite bricks. For the same volume, the weight is 15% higher.

Therefore, for parts with temperatures ≤1700 ℃ and frequent hot and cold cycles, such as ceramic firing kilns, hot blast stoves, and the transition zone of cement rotary kilns, mullite bricks can balance lifespan and cost.

In areas with temperatures ≥1750 ℃ ​​or strong alkaline corrosion, such as glass kiln arches or steel ladle slag lines, corundum bricks can be used directly to reduce kiln shutdowns for maintenance.

By accurately measuring the operating data and comparing it with the parameters mentioned above, you can choose the right one from the two options in one go.

Of course, choosing the right type of refractory brick requires an assessment of the overall budget. Therefore, a reliable refractory supplier is also crucial.

Henan Ruitai Lianxin Refractory Materials Co., Ltd. has been focusing on refractory materials for 20 years. It can not only provide customers with high-quality refractory bricks that meet the required standards, but also provide the most suitable kiln operating conditions solutions. Choosing Ruitai Lianxin is choosing strength.