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Any aggregate can potentially be used to form monolithic refractory materials. The type of materials used, which are often alumina-based cements or naturally-occurring aggregates, are often chosen based on their stability in high temperatures, their corrosion resistance and their mechanical strength.
Types of Refractory Aggregates
The following is a list of some of the more common aggregates used in refractory processes:
Bauxite
Bauxite is an ore that usually consists mostly of Boehmite or Gibbsite. In refractory applications, the bauxite is calcined in a rotary kiln, which produces a material made of corundum, mullite and a glassy phase.
Calcined and Sintered Alumina
Calcined aluminas have low levels of impurities when they are processed using the Bayer method. These aluminas are very stable, even at high temperatures, and are produced from bauxite
Fused Alumina
Upon producing fused alumina electronically in an arc furnace, the manufacturer will then cool this fused product into ingots, which are crushed and then classified. There are actually two different types of fused alumina: Brown, which is manufactured from bauxite, and White, which is formed using calcined alumina. White fused alumina has fewer impurities. These two types of fused aluminas tend to be present in refractories that are exposed to extremely severe conditions.
Fused Bubble Alumina
Fused bubble alumina is used for high temperature insulating in monolithic refractories. This type of alumina is made using a stream of high pressure air that is blown into molten alumina, forming bubbles in the material. The incomplete bubbles are separated at the end of this process.
Chamotte
Made from clay, chamotte is sintered to the point of no further shrinkage. The process involves the extrusion then firing of raw claw into a tunnel or rotary kiln. Mullite is the main phase of chamotte at high temperatures.
Vermiculite
Vermiculite is a clay mineral that is somewhat similar to mica and has a three layered structure. When it is heated to around 350 degrees Celsius, vermiculite begins to shrink. At higher temperatures, the combined water is released, causing exfoliation and a swelling of up to 10-20 times the original volume. The exfoliated material is not very strong, but it has a low thermal conductivity and makes ideal insulating material, such as that used for castables.
TFL, Incorporated
For a range of refractory products and services, visit the professionals at TFL, Inc. We pride ourselves on customer service, and are famous for helping our clients solve their refractory problems by using both technical know-how and engineering experience. Industries such as power generation, steel, lumber, minerals processing and furnaces turn to TFL, Inc. for all of their refractory needs and alumina-based cements. Call us today at 281-590-8500.
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