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What is white fused alumina ?
Corundum, or alpha alumina, is the most thermodynamically stable form of alumina. In fact the term corundum is generally applied when the alpha alumina has been produced by a fusion process. The alumina source is melted, typically in an electric-arc furnace, then slow-cooled, with the objective of forming an alumina single crystal on a macroscopic scale. Corundum is divided into three main groups:
- White corundum or white fused alumina (WFA) - “pure” alumina, including globular or bubble alumina
- Brown corundum or brown fused alumina (BFA) - aluminas with 1.5% or 3% TiO2, including semi-friable(TiO2 1.5%)
- Solid solutions with corundum matrices for example, zirconia alumina corundum (10, 25 or 42% of ZrO2) and aluminium oxynitrides (AlON).
In nature, corundum is the hardest mineral after diamond (9 on Mohs scale). Moreover, chemically inert with friability depending on its preparation, it has always been a multipurpose abrasive and remains the most commonly used today.
Also, it is used as an aggregate in refractories for its high temperature mechanical resistance, its dimensional stability, its chemical inertness and its electric resistivity. Moreover, it can be used as filler when an electric resistivity or a high friction coefficient is required.
Typically, alumina based raw materials are melted in a triphased electric arc furnace. For white fused alumina the raw material is pure calcined alumina. At Arc Fused Alumina our teams have all the know how to deal with all the parameters of the furnace to control the quality of the production :
- Adapt the chemical composition of the melt to the specifications of the targeted product;
- Adapt the electrical adjustments (power, voltage) to the targeted product and to the composition of the melt;
- Seek chemical and electrical stability of the furnace
- Adapt the flow and the spatial distribution of the products in the furnace to the injected electric power;
White corundum is more angular than brown corundum, it works faster and creates less heating. It is often used as a free abrasive (glass polishing). Its applications are vitrified grinding wheels, precision milling, rectification, sharpening of cutting tools, surfacing and fine rectification, where the heating of the part must be avoided (thermo-sensitive steel and alloys) and refractories.
Single crystals: They have numerous sharp edges guaranteeing a good bond with the matrix. They are very tough and difficult to blunt. Applications: plunge cut grinding.
Bubble alumina: Used to create porosity in high performance vitrified grinding wheel abrasives, agglomerated abrasives and high performance alumina refractories.