Samples of ruby, a red variant of corundum.
| IUPAC name
| Systematic IUPAC name
| Other names
|Molar mass||101.96 g/mol|
|Melting point||2,072 °C (3,762 °F; 2,345 K)|
|Boiling point||2,977 °C (5,391 °F; 3,250 K)|
|Solubility|| Reacts with halogenic acids and alkali|
Insoluble in organic solvents
|Vapor pressure||~0 mmHg|
Std enthalpy of
|Safety data sheet||Sigma-Aldrich|
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Aluminium oxide or alumina is the chemical compound of aluminium and oxygen, with chemical formula Al2O3. It's the most common and stable form of the aluminium oxides. Aluminium oxide occurs naturally in it's crystalline alpha phase as mineral corundum.
Aluminium oxide will react with sodium hydroxide to form sodium aluminate.
Aluminium oxide is a white solid compound, insoluble in water and solvent, but will dissolve in non-oxidizing acids. It is odorless and it's very hard (9 Mohs scale). It's an electrical insulator.
Aluminium oxide is often present in sandpapers, you can also buy it from mineral collectors as corundum or gemstones like ruby or sapphire. Certain smartphones have colorless transparent protective sheet of synthetic corundum.
Heating elements also contain alumina powder which acts as an insulator for the resistance wiring.
Aluminium oxide is a product of thermite reaction:
- M2O3 + 2 Al → Al2O3 + 2 M
This reaction also gives various aluminates, and separating the alumina from the slag is complicated and may not worth it.
A much better and simpler method involves the dehydration of aluminium hydroxide, which can be obtained by precipitating an aluminium salt with sodium or potassium hydroxide.
- Al(NO3)3 + 3 NaOH → Al(OH)3 + 3 NaNO3
Another route involves adding an acid to sodium aluminate, forming sodium salt of said acid and aluminium oxide/hydroxide. Excess NaOH can be added after the addition of the acid to prevent the formation of aluminium salts. Sodium aluminate itself is obtained from the reaction of sodium hydroxide and aluminium metal.
- NaOH + Al → NaAlO2 + H2O + H2
- NaAlO2 + H+ + NaOH → Na+ + Al(OH)3
Aluminium oxide can be obtained by calcinating aluminium hydroxide between 500-850 ºC:
- 2 Al(OH)3 → Al2O3 + 3 H2O
- Make aluminium salts
No special handling is necessary, though it's recommonded to avoid inhaling in in powdered form. Aluminium oxide isn't flamable or explosive.
Storage in closed bottles is adequate.
Aluminium oxide could be safely dumped with normal trash or spilled out in a soil.