2023-05-07

Aluminum Oxide – Alpha Phase

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Aluminum oxide (also known as alumina) is one of the most widely used of all industrial materials. It is a highly versatile oxide ceramic with excellent electrical and thermal properties. It can exist in a number of crystalline phases which all revert to the stable hexagonal alpha phase at elevated temperatures. This is the most commonly utilized form of alumina for structural applications. It is the strongest and stiffest of all oxide ceramics, has superior refractoriness and good dielectric properties.

The alpha alumina crystal structure can be described as having a face-centered cubic structure with oxygen stacking in a pattern known as ABCABC. This structure is very dense and non-porous. Alpha alumina also has trivalent aluminum cations filling the octahedral positions and occupying 2/3rds of the tetrahedral sites, resulting in a high level of occupancy. This structure is the primary product produced during the Hall-Heroult refining process of aluminium metal.

It is slow to dissolve in aqueous alkali solutions and in non-polar organic solvents. It is insoluble in water, but soluble in dilute hydrochloric acid. It is an amphoteric compound, reacting with both acids and bases. It has a low affinity for water, with only a few molecules binding to it at room temperature.

This white powder is a key ingredient in the production of advanced oxide ceramics and other materials. Its unique combination of reactivity and high heat transfer capabilities makes it a popular core and filler material for nanocomposites. It is also being investigated as a catalyst support due to its unique structure, low friction, and biocompatibility.

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