What is fused mullite brick?

Mullite bricks are refractory products made of mullite as the main phase. Because the main crystal phase of mullite brick is mullite, the fire resistance of mullite is about 1850C. High load softening temperature, low high temperature creep rate, good thermal shock resistance, and acid corrosion resistance.

 

The fused morocco brick uses high alumina bauxite as raw material, and different bauxite is mixed into mullite slag (3Al, 0, .2SO3, the mass percentage is Al: O, 72% 9 SO.28%). It melts around 2300C, is cast into the sand mold at 1850C, and 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% to 8.5%) of cobalt dioxide can make the mullite crystals smaller and the brick structure denser. The mullite amount can be increased to 60% to 70%, which relatively reduces the glass phase content 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.

When manufacturing fused mullite bricks, corundum crystals are first precipitated during cooling, and then mullite crystals are precipitated. The remaining small amounts of SO2, Al2O3, Fe203 ~ CaO, M2O, NazO, 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 the SO2 will become gaseous so leaving the brick body. At temperatures above 1650C, mullite will decompose even at lower oxygen partial pressures, rather than reducing atmospheres.