Cordierite mullite refractory slab adopts coordinate (with granularity of 1~0.5mm, 0.5~0.2mm, 0.088 mm) and mullite clinker (M60, 1~0.5 mm) as primary raw material, added with 25%(w) powder mixture composed of under burnt MgO powder, α-Al2O3 micro powder and additives(knar clay and KOH). The weight ratios of cordierite and mullite are prepared on the basis of 40:35, 42.5:32.5 and 45:30. After mixing, molding, the green body is sintered at 1300℃, 1350℃, 1400℃ for 3h, respectively. The samples of cordierite mullite refractory slab is tested for the room temperature and high temperature physical performances, meanwhile, XRD,SEM and EDS analysis are also carried out. The test result suggests that refractory slab has the best performance indexes when raw material’s cordierite mullite weight ratio is 45:30, and sintered at 1350℃. Its principle crystalline phase is coordinate and mullite, and he microscope structure is homogeneous, large quantity of coordinate crystal grains and mullite crystal grains are formed, the connection bridges between aggregates develops very well, material have relatively high modulus of rupture.
Cordierite mullite refractory slab and the preparation method. Aggregates of coordinate mullite refractory slab include: mullite grain, fireclay, matrix includes talc powder, kyanite, andalusite, magnesium powder, alumina powder. The prepared matrix and aggregates are fully grinded in wheel grinder, then after screening, ageing in enclosed atmosphere and molding by hydraulic pressing machine, the green body is dried in airtight condition and quickly sintered in high temperature kiln. This production method is simple and with easy workability, refractory slab has excellent thermal shock resistance, high modulus of rupture at room temperature and high temperature, significant energy saving effect during application, and can thoroughly solve the defect of contamination. The energy consumption is decreased and rate of finished products is increased. This refractory slab is the ideal refractory kiln furniture product as well as furnace body structural material, it is widely used in domestic ceramics, sanitary ceramics, building ceramics, industrial ceramics, technical ceramics, glass ceramics, magnetic materials, powder material calcining, metallurgy and so on.
Refractory slab is the key kiln furniture applied in domestic ceramics, sanitary ceramics and other ceramics industries, the shape of refractory slabs are mainly thin board type, with large surface area and relatively low thickness. During using, refractory slab has the function of supporting the green body that is to be sintered. It is delivered into kiln along with the green body, as it contact with flame directly, and the sintering temperature is so high that the requirement on refractory slab is very high.
First, refractory slab should have very good high temperature modulus of rupture, high refractoriness under load temperature, won’t bend or deform during supporting large weight of sintered products.
Second, refractory slab should have excellent thermal shock resistance, during the process of recycling using, won’t crack or damage under quick cooling and quick heating temperature change.
Third, refractory slab should have nice oxidization resistance, won’t react with products during sintering, or contaminate the sintered ceramic products.
Forth, refractory slab should have low expansion coefficient, small reheating linear change rate and good volume stability.
Fifth, to meet the requirement of energy saving and emission reduction, refractory slab should adapt to quick sintering tempo, i.e., have good quick cooling resistance and quick heating resistance. Meanwhile, to reduce the ratio of kiln furniture energy consumption, refractory slab need to have high modulus of rupture at high temperatue.
Currently, kiln furniture materials mainly are fireclay and mullite based, the service life is only tens or several tens of times. Only a little quantity of re-crystallization refractory slab kiln furniture is used. Re-crystallization refractory slab has good high temperature physical performance, such as high thermal conductivity, low thermal expansion coefficient and won’t have plastic deformation at 1700℃, its working temperature is far higher than other kiln furniture, but itself is a new type of black ceramic material, is easy to react with ceramic products and pollute them, what’s more, the production cost is high, production is very difficult, so it is very hard to be applied in large scale. Fireclay and mullite base kiln furniture mainly adopts fireclay and mullite, their main defects are short service life, easy to expand or even deform.
The weight percent of coordinate mullite refractory slab raw materials are: 35~40% of mullite grain, 20~27% of fireclay, 12~18% of talc powder, 7~10% of kyanite, 5~9% of andalusite, 4~9% of magnesium powder, 2~7% of alumina powder.
The procedures of making cordierite mullite refractory slab
1. Matrix preparation: 12~18% of talc powder, 7~10% of kyanite, 5~9% of andalusite, 4~9% of magnesium powder, 2~7% of alumina powder.
2. aggregate preparation: 35~40% of mullite granule, 20~27% of fireclay.
3. The prepared matrix and aggregate are adequately grinded in wheel grinder with proper quantity of water, the milling time should be no less than 30h.
4. Screening and selecting.
5. Material Enclosed ageing, the time should be equal or higher than 20h.
6. Molded to green body by hydraulic pressing machine.
7. Dried at airtight condition, adopting dry racket as supporter, the moisture is 30~50%, temperature is about 80~130℃, the drying time is between 12~24h.
8. Kiln loading as soon as drying is finished, ensure the green body is perpendicular to the supporting board, i.e., beam or silicon carbide slab. The flatness can be measured by plumb and leveling instruments, and the green body should be separated by holding strip every 6cm, and then new green body can be loaded.
9.High temperature sintering. The sintering temperature should be higher than 1370℃, and the sustaining time of highest temperature should be longer than 10h.
