Properties of Mullite Brick

The properties of mullite brick is up to the properties of mullite. It has high refractoriness, high softening temperature under load, high creep resistance at high temperature, excellent thermal shock resistance, good slag corrosion resistance and high shear modulus. Mullite brick finds wide use in the high-temperature hot stove, large-scale blast furnace hearth and bottom, steelmaking furnace roof, ceramic lining of industrial kilns, kiln tools and the lining of glass furnaces and cement kilns. 

Mullite brick are mainly made in two ways: sintered mullite brick and fused mullite brick. The sintered mullite brick is made of mullite as raw materials and has good corrosion resistance and thermal shock resistance. 

 

Fused mullite brick is made of fused mullet. It is mainly used in the glass furnace. it has high mechanical strength and deformation temperature under load. It has high bulk density, low porosity, and high crystalline phase content. There are no abnormal phenomena in the thermal expansion curve. However, at high temperature, when in contact with a large number of alkali substances, mullite is unstable and easily decomposed, which reduces the stability of these refractory to a certain extent.

 

In addition, fused mullite with different purity can produce fused mullite brick with different properties. Even if the purity of fused mulltie is the same, they can have different properties with different fusing process. 

 

In general, sintered mullite brick has better high temperature flexural strength than fused mulltie brick, because there are small but well grown crystal networks in the former. The later has larger crystals and good volume stability and creep resistance. Furthermore, fused mullite brick has better corrosion resistance than sintered mullite brick with the same chemical composition. 

 

Mullite brick should not be in contact with alkaline substances above 1450℃, otherwise mullite will decompose. In a reducing atmosphere of more than 1370%, mullite will decompose and some SiO2 will be gasified and leave the brick. When the temperature is higher than 1650 ℃, if not in a reducing atmosphere but at a lower partial pressure of oxygen, mullite will decompose. From this, the combustion temperature will directly affect the firing of mullite brick. 

 

Although mullite brick is more expensive than high alumina brick, it has wide application due to its superior performance.