Alumina and Alumina Refractories...

Alumina and Alumina Refractories Alumina (Al2O3) refractories are the part of alumina- silica (SiO2) group of refractories and belongs to the SiO2 -Al2O3 phase equilibrium system as shown in diagram at Fig 1. They differs from fire clay refractories in term of Al2O3 content and normally have Al2O3 content of more than 45 %. The raw material base for these refractories are different than the fire clay bricks. Fig 1 SiO2 – Al2O3 phase diagram As seen in the diagram, refractoriness increases with the increase in the Al2O3 content. The eutectic at 1595 deg C has a composition of 94.5 % SiO2 and 5.5 % Al2O3. As the Al2O3 content is increased, the melting point of the refractory increases to a maximum of 2054 deg C which is the melting point of pure corundum. The only stable compound in the system is mullite, which has a defective space lattice and decomposes into corundum and liquid phase at around 1840 deg C. The classification of Al2O3-SiO2 refractories as per the Al2O3–SiO2 phase equilibrium diagram is given in Tab 1. Tab 1 Classification of Al2O3-SiO2 refractories as per the Al2O3–SiO2 phase equilibrium diagram Range of Al2O3  Phases as per common terminology General performance of refractories in conditions of the absence of slag corrosion or alkali attack Al2O3 less than 50 % Fireclay (Chamotte); Phases on phase diagram are mullite and glass; can contain free SiO2 Normally made from 100 % fireclay, Highest quality grades (super duty bricks) usable to about 1600 deg C,  Usually contain 38 % to 42 % Al2O3 and are based on fireclay minerals Al2O3 50 % or 60 % Sillimanite, andalusite, or kyanite; Phases on phase diagram are mullite as major phase and glass as minor phase; can contain free SiO2 These...