Corundum and alumina are chemically identical, both consisting of aluminum oxide (Al2O3), but their physical forms and crystal structures are significantly different, so they differ in practical applications and properties. Here is a detailed comparison of the two:
1. Chemical composition
– Alumina (Al2O₃): It is an oxide of aluminum with the chemical formula Al2O₃, which is widely found in nature or synthesized industrially.
– Corundum: It is the crystalline form of aluminum oxide (α-Al2O₃), which is the most stable crystal form of Al2O₃.
– Corundum: It is the crystalline form of aluminum oxide (α-Al2O₃), which is the most stable crystal form of Al2O₃.
corundum and alumina
2. Differences in structure and properties
| Characteristic | Corundum (α-Al₂O₃) | Other forms of alumina (such as γ-Al₂O₃) |
| Crystal structure | Hexagonal close-packed structure, highly ordered | Cubic or disordered structure, high porosity |
| hardness | Mohs hardness 9 (second only to diamond) | Low hardness (usually in powder or loose form) |
| Thermal stability | Very high (melting point 2054℃) | Lower, may be converted to α type at high temperature |
| Common forms | Natural minerals (such as ruby, sapphire) | Industrial synthetic powder, catalyst carrier, etc. |
3. Application fields
– Corundum:
– Gemstone: Ruby (Cr³⁺) and sapphire (Fe²⁺/Ti⁴⁺) when containing trace impurities.
– Industrial use: Abrasives (sandpaper, grinding wheels), refractory materials, precision instrument bearings.
– Gemstone: Ruby (Cr³⁺) and sapphire (Fe²⁺/Ti⁴⁺) when containing trace impurities.
– Industrial use: Abrasives (sandpaper, grinding wheels), refractory materials, precision instrument bearings.
– Alumina (non-corundum form):
– Catalyst carrier: γ-Al₂O₃ is used for catalytic reactions due to its high specific surface area.
– Adsorbent: Purify impurities in water or gas.
– Ceramics and fillers: Used in electronic components and composite materials.
– Catalyst carrier: γ-Al₂O₃ is used for catalytic reactions due to its high specific surface area.
– Adsorbent: Purify impurities in water or gas.
– Ceramics and fillers: Used in electronic components and composite materials.
4. Summary
– Connection: Corundum is a form of aluminum oxide, with the same chemical nature.
– Difference: Corundum refers specifically to α-Al₂O₃ crystals with high hardness and high stability, while aluminum oxide refers to all forms of Al₂O₃, including amorphous and other crystalline forms.
In simple terms: Corundum is the “diamond form” of aluminum oxide, while ordinary aluminum oxide may be the “graphite form” – the same composition, different structures lead to different performances.