Do You Know What is Fused Mullite Brick?

Mullite brick is a silica-aluminum system refractory product with mullite as the main crystal phase. Because the main crystalline phase of mullite brick is mullite, the refractory degree of mullite is about 1850C. If the softening temperature is high, the high-temperature creep rate is low, the thermal shock resistance is good, and the acid corrosion resistance.
 

The fused morocco brick uses high alumina bauxite as raw material, and different bauxite is mixed into mullite slag (3Al2O3.2SO2, the mass percentage is AlO372%, S028%). It melts at around 2300C, is cast into the sand mold at 1850C, and is then annealed to eliminate stress. The main crystal phases are mullite and corundum, and the glass phase is filled between the crystal phases.
 

Its resistance to liquid glass erosion is stronger than sintered refractories, but not as good as other fused refractory materials. Adding a small amount (7% ~ 8.5%) of zirconia can make the mullite crystals smaller and the brick structure denser. The mullite amount can be increased to 60% ~ 70%, which relatively reduces the content of the glass phase and reduces Cracks in the product. Fused mullite bricks have low thermal expansion coefficient, good thermal shock resistance, and strong resistance to the erosion of glass liquid.

In the manufacture of fused mullite bricks, corundum crystals are first precipitated during cooling, and then mullite crystals are precipitated. The remaining small amounts of SO2, Al2O3 ~ Fe2O3, CaO, MgO, Na2O, etc. finally become a glass phase. The glass phase accounts for 25% of the brick. It contains many low-melting substances, so its corrosion resistance is worse than other fused bricks. Air bubbles and reducing substances are also present in the glass phase, which contaminates the glass liquid during use.
 

Mullite bricks should not be in contact with alkaline substances above 1450C, otherwise mullite will be decomposed. In a reducing atmosphere above 1370C, mullite will also decompose, and part of S02 becomes gaseous so leaving the brick body. At temperatures above 1650 ° C, mullite will decompose, even at a lower oxygen partial pressure, instead of a reducing atmosphere.