Fused cast mullite bricks are aluminao-silicate series refractories, mainly composed of mullite crystalline phase. Since the principle crystalline phase of fused cast mullite brick is mullite, which has a refractoriness of about 1850°C, high refractoriness under load temperature, small high temperature creep rate, good thermal shock resistance is and acid corrosion resistance. Fused cast mullite bricks have excellent high temperature performances.
Fused cast mullite bricks are made from high alumina bauxite, different grades of bauxite are mixed proportionally to have identical components with mullite (3Al2O3·2SiO2, the mass percentage of Al2O3 is 72%, and that of SiO2 is 28%). The raw material is melted at about 2300 °C, casted in sand mold at 1850°C, and then annealed to eliminate stress. The main crystalline phase is mullite and corundum, with glass phase filled between the crystalline phases.
Fused cast mullite bricks have better molten glass corrosion resistance compared with sintered mullite bricks, but not so good as other fused refractories. So if a small amount of zirconia (7%~8.5%) can be added into the raw material, which can make the mullite crystal smaller, brick structure will be denser, mullite phase can reach to 60%~70%, correspondingly, glass phase content will decline, so there will be lower cracks in fused cast mullite bricks.
Fused Cast Mullite Bricks Properties
High refractoriness and refractoriness under load temperature.
Low thermal expansion coefficient.
Good thermal shock resistance and strong resistance to molten glass corrosion.
Fused cast mullite bricks physiochemical index
Item
Unit
Index
Al2O3
%
72~74
SiO2
%
24~26
Fe2O3
%
<0.8
True Specific Gravity
g/cm³
3.54
Apparent Porosity
%
8
Cold Crushing Strength
Mpa
350
Thermal Expansion at 1150℃
%
0.8
Thermal Conductivity at 500-1500 ℃
W/m.k
4.6
Fused Cast Mullite Bricks Application
When making fused cast mullite bricks, corundum crystal is first precipitated during the cooling, and then mullite crystal. A small amount of SiO2, Al2O3, Fe2O3, CaO, MgO, Na2O and other oxides finally form glass phase. The glass phase accounts for 25% of the bricks. It contains many low-melting substances, so the corrosion resistance is weaker than other fused bricks. Bubbles and reducing substances are also present in the glass phase, which can contaminate the glass during application.
Fused cast mullite bricks are mainly used for parts that need wear-resistant and high-temperature resistant materials, such as sliding-rail bricks of metallurgical Pusher-type heating furnace, walking-type heating furnace tapping platform (tapping spout) and garbage incinerator lining.
