The key difference between alumina and corundum is that alumina is the name of the group of compounds having the chemical formula Al2O3, whereas corundum is the naturally occurring mineral of aluminum oxide compound.
Alumina and corundum are important inorganic chemical compounds. These compounds contain aluminum oxide in their composition.
What is Alumina?
Alumina is the oxide of aluminium with the formula Al2O3. It is a white colour crystalline solid. Since aluminium is too reactive, we cannot find it naturally in free form (very rarely, we can find free Al). In nature, aluminium is covered with an oxide layer, and this surface aluminium oxide layer protects it from corrosion.
Moreover, the molecular weight of alumina is about 102 g mol-1. Its melting point and boiling points are very high, which are over 2000°C. In addition, this compound is water-insoluble but very hygroscopic. Although alumina cannot conduct electricity, it is a thermal conductor. Since aluminium is an amphoteric element, aluminium oxide is also an amphoteric oxide.
Alumina occurs commonly in the form of corundum, which is a crystalline mineral. It is useful in producing aluminum metal by the Hall process. In this process, alumina is dissolved in molten cryolite, and the resulting salt is electrolyzed. After that, we can obtain pure aluminium metal.
Moreover, we can use this compound as an abrasive due to its hardness and strength. It is also useful as a catalyst to enhance chemical reaction rates. In addition, it is useful as a water absorber to purify gases and filler for plastics.
What is Corundum?
Corundum is the mineral form of aluminum oxide. It is a crystalline form of Al2O3. It contains traces of iron, titanium, vanadium, and chromium. We can describe it as a rock-forming mineral. Naturally, it is a transparent material. However, it can have different colors based on the presence of transition metals as impurities in the crystalline structure.
Moreover, corundum contains two primary gem varieties known as ruby and sapphire. Typically, rubies are red because there is chromium, while sapphires appear in a range of colors based on the type of transition metal present in the mineral.
Corundum is an oxide mineral in the hematite group. It has a trigonal crystal system and a hexagonal scalenohedral crystal class. The crystal habit can be given as steep bipyramidal, tabular, prismatic, etc. The twinning is polysynthetic twinning, which is common. It has no cleavage that parts in 3 directions. Further, corundum is a brittle material, and its fracture is conchoidal. The hardness, according to the Mohs scale, is 9. It has an adamantine luster, and the streak color is colorless.
What is the Difference Between Alumina and Corundum?
Alumina and corundum are related chemical compounds consisting of aluminum. The key difference between alumina and corundum is that alumina is the name of the group of compounds having the chemical formula Al2O3, whereas corundum is the naturally occurring mineral of aluminum oxide compound.
The following table summarizes the difference between alumina and corundum.
Summary – Alumina vs Corundum
Alumina is a white colour crystalline solid, while corundum is the mineral form of aluminum oxide and a crystalline form of Al2O3. The key difference between alumina and corundum is that alumina is the name of the group of compounds having the chemical formula Al2O3, whereas corundum is the naturally occurring mineral of aluminum oxide compound.
1. “Alumina.” Encyclopædia Britannica, Encyclopædia Britannica, Inc., 28 Nov. 2018.