| Item |
Cordierite Mullite |
| Al2o3 |
39 |
| SiO2 |
48 |
| MgO |
7.0 |
| Bulk Density(g/cm3) |
1.85 |
| Show Porosity(%) |
28 |
| 20℃ Flexural strength (Mpa) |
11.2 |
| 1250℃Flexural strength (Mpa) |
8.7 |
| 200-1000℃Expansion coefficient |
0.79 |
| 20℃Specific heat（KJ/Kg. K） |
1.0 |
| The highest working temperature |
1300℃ |
Cordierite is the special grade raw material for the production of high-performance thermal shock resistant refractory products, with the addition of cordierite(MgO：13.8％、Al2O3：34.8％、SiO2：51.4％), its content will be high in the final products. Cordierite refractories have high mechanical strength, low thermal expansion coefficient, their modulus of rupture is as high as 95Mpa, linear expansion coefficient is about 2.0×10-6℃-1 between 20~800℃. Cordierite bricks are mainly used as a refractory slab, regenerator slabs, base plate, porous plate, push plate, supporting bricks, and so on. High thermal shock resistant cordierite refractories are usually produced by α-Al2O3 talc, Suzhou clay, while regular thermal shock resistant cordierite bricks are made by talc, chamotte and bauxite.
Mullite is the general name of aluminum silicate series minerals. Mullite is a chemically stable binary compound of Al2O3-SiO2 series compounds. Except for the mullite (3Al2O3·2SiO2) phase, mullite refractories with lower Al2O3 content also have a little amount of glass phase and cristobalite, those with higher alumina content also have a little corundum phase.
What is cordierite mullite brick?
Cordierite mullite brick adopts sintered mullite, andalusite, tabular corundum, and cordierite as the main raw material, added with ultra-micro powder to reinforce the matrix. The processing procedures of cordierite mullite bricks are mixing, molding, drying, and sintering, As the sintering temperature zone of cordierite, is very sharp, sintering temperature control is the key factor for its quality. Mullite cordierite bricks produced by this craft not only have excellent thermal shock resistance(after 100 times of 1100℃ water cooling test, there is no crack) but also have excellent high-temperature performances( refractoriness under load is higher than 1500℃). Mullite cordierite bricks are popularly used in the ceramic industry such as kiln vehicle surface, porous push plate, roller kiln gasket, sagger, and so on, as well as the ceramic combustor of hot blast furnaces.
The raw material composition of thermal shock resistant cordierite mullite bricks is between Al2O3-MgO-SiO2 ternary series cinoenstatite and cordierite, the sintering range is very narrow. The raw material consisted of Kaolin and 10~30% of talc has a sintering scope of 90~240℃. When talc content is 40%~70%, the sintering scope drastically drops to 10~30℃. The green body composed of 30%~40% talc, 30~40% of plastic clay, and about 20% of calcined Al2O3 can produce porous refractory products with excellent thermal shock resistance. When sintered at 1380℃~1410℃, products with 60% of cordierite can be obtained. To get as much cordierite as possible, and to avoid cordierite discomposing into mullite and glass phase during high-temperature sintering, the raw material can be proportionally mixed, molded, and sintered at 1350℃ to pre-synthesize cordierite, and then ground to powder, molded again, and finally sintered at 1400℃. The produced cordierite bricks have an expansion coefficient of 1.4×10-6℃-1.
Cordierite mullite bricks have good thermal shock resistance, small thermal expansion coefficient. Between 20~100℃, the linear expansion coefficient of porous cordierite products is only (1～1.2)×10-6·℃-1, at 20～200℃, the linear expansion coefficient is（1～1.5)×10-6℃-1, while it is 2.0×10-6℃-1 between 20~800℃. Since the forming temperature range of cordierite is very narrow, under burned products don’t have enough cordierite, while over burnt cordierite decomposes into mullite and glass phase again. So, adopting high alumina cordierite mullite-based raw materials can not only enlarge cordierite forming temperature range, but also avoid cordierite decomposition in high temperature, as well as the enhancement of quality.
Cordierite mullite bricks have better performance than fireclay cordierite products. According to the forming properties of cordierite, the sintering temperature should not raise too quickly at the range of 900~1200℃, so crystal water can be evaporated and talc can be better decomposed. Cordierite is formed at 1200~1300℃, so the sintering time at this temperature should be promised to obtain more cordierite, temperature ascending speed should be slow and stable at this temperature zone.
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