Now, the common fused cast refractories, according to the chemical composition, include Al2O3-SiO2 fused cast refractories, fused cast alumina refractories, fused cast AZS refractories, fused cast high zirconia refractories and Cr2O3 fused cast refractories. 

1) Al2O3-SiO2 fused cast refractories

Al2O3-SiO2 fused cast refractories are made of bauxite as the main raw material with a crystallization organization with mullite and corundum as the main body. It was used in the glass furnaces early, but now it has been replaced by other refractories and seldom used in glass furnaces. However, it has good wear resistance due to its dense and strong structure. It is suitable to the rails of the steel furnaces and hearths of the soaking zone. 

 

2) Fused cast alumina refractories

According to the crystallographic analysis, the fused cast alumina refractories can be divided into α-alumina block, α-βalumina block and β-alumina block. 

 

α- fused cast alumina block consists of more than 99%α-alumina. It has dense and strong organization and high hardness. It has excellent stability at high temperature. It is usually used in the ling of the firing zone in high-temperature tunnel kilns and burners. 

 

α-β- fused cast alumina block consists of about 50% α-alumina and β-alumina. The two crystals are intertwined with each other and form a dense structure. It has excellent resistance to acids and alkalis. At high temperature (>1350℃), it has better corrosion resistance better than AZS, but below 1350℃, they have the same corrosion resistance. Since it contains no impurities (Fe2O3, TiO2, etc.) and only a small amount of matrix glass phase, it has a low potential of bubbling and pollution. Therefore, it is used in the low temperature parts of glass furnaces, such as the refining zone, feeder channel and forehearth. 

 

β- fused cast alumina block consists of almost 100%β-alumina. It has large plate-like β- alumina crystalline structure. Its crystals are intertwined and thin. It has high porosity and low strength. It has high spalling resistance and especially high corrosion resistance to alkali vapor, so it is used in the upper structure of dry glass tank kilns. 

 

3) Fused cast AZS refractories

Fused cast AZS has a dense structure formed with intertwined corundum and baddeleyite crystals with 20% viscous glass phase filled in the gaps. Since it has good corrosion resistance to alkalis, it is used in the parts in direct contact with glass liquid, the upper structure and regenerators. It is the most widely used fused cast refractories. 
 

According to the ZrO2 content, fused cast AZS blocks can be divided into 33# AZS block, 36# AZS block and 41# AZS block. AZS refractories undergo a crystalline transformation between monoclinic and tetragonal crystals at 1150℃ when the temperature rises and at 900℃ when the temperature drops, accompanied with volume shrinkage and expansion. But, the volume shrinkage can be absorbed by the matrix glass phase. Therefore, even large block can be manufactured without cracks. 

 

4) Fused cast high zirconia refractories

Fused cast high zirconia block is composed by more than 90% baddeleyite and a small amount of glass phase. Since it has high content of ZrO2 and low content of glass phase, it has good corrosion resistance and low potential of bubbling. Moreover, compared to AZS, it is composed of only ZrO2 without Al2O3, so it does not form a reaction layer when in contact with molten glass and maintain a clear interface. Therefore, it has a low potential of pollution due to the generation of alumina striae. Therefore, zirconia has recently achieved good results in the production of high quality glass. 
 

5) Cr2O3 fused cast refractories

Cr2O3 fused cast refractories include fused cast magnesia chrome refractories, fused cast chrome alumina refractories and AZSC (Al2O3-ZrO2-SiO2-Cr2O3). Fused cast magnesia chrome refractories are mainly used in the steel furnaces and the other two are used in the glass furnaces. 

 

Fused cast chrome alumina refractories are composed of intertwined Cr2O3-Al2O3 solid solution and spinel crystals which results in a compact structure. It has excellent corrosion resistance to molten glass. However, although Cr2O3 has good corrosion resistance, it can color the glass liquid. So, it is limited to the production of colored glass and glass fiber.