Mullite brick is a kind of fire brick which uses synthesized mullite as raw material and the principle crystalline phase is mullite. When Al2O3 content is lower than mullite theoretical ratio, mullite brick contains small amount of periclase. When Al2O3 content is higher than theoretical proportion of mullite, there is a small amount of corundum. Mullite products have better high temperature creep property than high alumina bricks made from natural bauxite. Mullite bricks’ high temperature property is equivalent to silica based products and magnesia based products. Mullite fire bricks also have better acid slag resistance and weak basic slag corrosion resistance than magnesia products. There are two kinds of mullite refractory bricks: sintered mullite bricks and fused cast mullite bricks.
Mullite Bricks Characteristics
Good thermal shock resistance
Low high temperature creep rate
Good acid and weak alkaline slag corrosion resistance.
High refractoriness and mechanical strength.
Sintered mullite bricks
Sintered mullite bricks adopts synthesized mullite aggregates, and fines, or white corundum, quartz and pure clay powder mixture with the same chemical composition of mullite. The raw material is evenly mixed, then molded under high pressure and finally sintered at the temperature of 1550~1600℃.
Sintered mullite bricks physiochemical index
Item
Hot blast furnace mullite brick
Stopper head mullite brick
Blast furnace wall brick
Fused synthesized mullite brick
Al2O3 %
80.0
68.3
72.0
75.1
SiO2 %
18.2
—
—
20.1
Fe2O3 % ≤
0.76
0.84
1.7
3.35
Apparent porosity %
15.6-16.5
≤16.7
≤22
12-16
Cold compression strength/Mpa
197-267
≥77
≥49
210-250
Rupture under load/℃
≥1700
≥1600
≥1650
≥1700
Bulk density g/cm3
2.77-2.79
2.53
2.68
2.56-2.66
Fused cast mullite bricks
Fused cast mullite bricks’ main raw materials are high alumina bauxite or industrial alumina, clay or silica with proper ratio. The mixed material are melted in electric arc furnaces, casted into shape and then annealed to make the final mullite bricks. The main mineral ingredient of fused cast mullite bricks is mullite, which’s chemical composition is 3Al2O3·2SiO2.
Fused cast mullite bricks physiochemical property
Item
Hot blast furnace mullite brick
Al2O3 %
70.1-75.47
SiO2 %
19.32-21.6
Fe2O3 %
0.92-1.90
Apparent porosity % ≤
10
Cold crushing strength/Mpa
250-500
Rupture under load/℃
1700
Bulk density g/cm3
2.9-3.3
Refractoriness ℃
1730-1800
Thermal expansion rate %(20-1000 ℃)
0.60-0.65
Mullite Bricks Applications
Mullite bricks are mainly used in the inner lining of various parts of thermal kilns and furnaces for different industries, such as steel and iron industry, chemical industry, glass industry, ceramic industry and so on. For example, mullite bricks are widely used in hot blast furnace for iron making, used in glass kiln main body feeding channel, regenerative chamber, clarification tank wall. Mullite bricks are also used in rotary cement kiln and rotary lime kiln inner lining. The physiochemical index of mullite bricks are different for different applications.
