Aluminium Oxide or alumina (Al2O3) is one of the most versatile of refractory ceramic oxides and finds use in a wide range of applications. Alumina refractories are the part of alumina- silica group of refractories. Different from fire clay refractories, high Alumina refractories normally have Al2O3 content of more than 45%.
The raw material base for these refractories are different than the fire clay bricks. For the production of high Al2O3 refractories, both natural raw materials (such as kyanite, sillimanite, andalusite, and bauxite etc.) as well as synthetic materials (sintered mullite, fused mullite, calcined alumina, sintered corundum, and fused corundum etc,) are used.
Alumina (Al2O3) has the physical stability such as melting temperature, hardness, resistance to abrasion, and high mechanical strength. The material has the same chemical composition but have a different crystal structure which is α- Al2O3, β-Al2O3 and γ- Al2O3. The melting point, refractoriness, corrosion resistance and strength of alumina refractories increase with the increase in the Al2O3 content.
Based on the content of alumina, high alumina refractory is classified into 50%, 60%, 70%, 80%, 85%, 90% and 99%.
Refractories with 90 % and 99 % Al2O3 are among the highest strength and erosion resistant refractories. They can be used for temperatures greater than 1800℃。The most widely used alumina refractory with more than 90% Al2O3 content used in glass furnaces is Fused cast Alumina Block and Alumina Bubble block. There are three types of Fused cast Alumina Block: α Alumina, β Alumina and α-β Alumina. Fused cast Alumina Block α Alumina is an ideal product for the lower temperature zones of the glass melting furnaces due to its high density, superior corrosion resistance and low blister potential. β Alumina is the best material for molter crown, port crown, and feeder channel due to its high resistance to alkali vapor and excellent thermal shock resistance. α-β Alumina is widely used in working tank, feeder channels, superstructures and lipstone due to its excellent corrosion resistance against molten glass and no contamination to molten glass under 1350 ℃. Alumina Bubble block has low bulk density, excellent insulating properties and high hot strengths. These features make it an excellent insulating material that can withstand exceptionally high temperatures. It is always used as back-up insulation behind other refractories.
High alumina refractory with about 70% Al2O3 contains mullite as a major phase. It is made of bauxite. It can be used for temperatures greater than 1750℃. Mullite brick and high alumina brick belong to this group. Mullite brick is characterized by good high temperature resistance and good thermal shock resistance, which comes into being mullite through calcine with clay, high alumina materials and ceramics. It is mainly used in fibrous glass furnace. High alumina brick is made of high-quality bauxite clicker. It features high chemical corrosion resistance and high refractoriness. It is usually used in hot areas in glass melting tanks without glass contact.
Refractories containing 50 % and 60 % Al2O3 exhibit improved refractoriness over fireclay products. High alumina insulating brick is a new type of lightweight insulating material which contains approximately 48% alumina, mullite and glass phase or corundum. It has advantages such as high porosity, small volume density, good insulation effect, high mechanical intensity, small thermal conductivity and long service life. It is widely used in insulating layers of glass furnaces. Sillimanite brick is a kind of refractoriness which made by sillimanite and other minerals. And silimanite can be transformed to be mullite under more 1500℃ high temperature. It is mainly used in rider arches, forehearth and bushing for fiber glass furnaces.
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