High Alumina Series is generally supposed to be aluminium silicate product with high content of Al2O3 (48%). It is batched according with a certain proportion of both aggregate and powder, and produced with high temperature combustion of more than 1350-1560ºC.
In China, there are 4 kinds of high alumina products being commonly defined, according to different contents of Al2O3:
Super alumina brick (A2204)-Al2O3 standard content: ≥80%;
First class high alumina brick (A2203)-Al2O3 standard content: 75% ;
Second class high alumina brick (A2202)-Al2O3 standard content: 65%;
Third class high alumina brick (A2201)-Al2O3 standard content: 55%.
After proper adjustments of components based on the request of use, the series can also be divided into high alumina bricks, low-creep high-alumina bricks, high refractoriness under load alumina bricks, phosphate bonded high-alumina bricks, low-expansion high-alumina bricks and other segment types.
The series is mainly used in flues, regenerator, outside wall and other parts of glass furnace. And it can also be applied to the lining of metallurgy blast furnace, hot blast furnace, top of electric furnace , blast furnace, reverberatory furnace and rotary furnace.
High alumina series has good refractoriness, high refractoriness under load and its slag resistance is obviously improved with an increasing content of Al2O3. More specifically, high alumina product has following properties:
High alumina product is supposed to be a high-grade refractory material. Its refractoriness (1750-1790ºC) is higher than that of clay products and semi-silica products. Refractoriness is mainly influenced by contents, types and quantities of Al2O3. With an increasing of Al2O3 content as well as a decreasing of impurities content, the refractoriness will be improved.
5.2 Refractoriness Under Load
Because of a high content of Al2O3 with lower impurities in the series, the quantity of vitreum which can be easily melted is quite low. Therefore, its refractoriness under load is higher than that of clay series. However, its temperature of refractories under load is still lower than that of silicon series due to a lack of network structure formed by mullite crystallization.
5.3. Thermal Conductivity
Thermal conductivity of high alumina product is better than that of clay product. Because, in high alumina series, the quantity of glass phase which owns a lower thermal conductivity is very low. Besides, the increase of quantities of mullite and corundum crystal which owns good thermal conductivity obviously improves the capacity of heat transmission of high alumina series.
5.4 Thermal Shock Resistance
Thermal shock resistance of high alumina series is between that of clay and silicon. The times of water cooling cycle at 850ºC can reach to 35. The main reason is thermal expansibility of corundum is higher than mullite and no crystal can be transformed. So far, in order to improve the thermal shock resistance, it should change and improve particle structure of products, reduce content of fine powder and increase critical size as well as particle size distribution of clinkers.
5.5. Slag Resistance
High alumina series contains a good proportion of Al2O3 and is very close to neutral refractory materials. It can resist the corrosion of acid slag as well as alkaline slag. Due to the content of SiO2, the resistance of alkali slag is a little weaker than that of acid slag. In addition, slag resistance of high alumina product is related to product stability in the slag. Generally speaking, products which are processed by high pressure molding and high temperature combustion will own lower porosity and higher slag resistance.
Physical and Chemical Indicators