Difference Between Aluminum Oxide and Silicon Carbide

Main Difference – Aluminum Oxide vs Silicon Carbide

Aluminum oxide is also known as alumina. It is an oxide of aluminum. It is naturally occurring as either corundum or bauxite. Silicon carbide is a semi-conductor material. It is an inorganic compound. It is very rare on earth crust but is common in space as stardust. The main difference between aluminum oxide and silicon carbide is that aluminum oxide is an electrical insulator whereas silicon carbide is a semi-conductor.

Key Areas Covered

1. What is Aluminum Oxide
– Definition, Chemical and Physical Properties, Chemical Structure
2. What is Silicon Carbide
– Definition, Chemical and Physical Properties
3. What is the Difference Between Aluminum Oxide and Silicon Carbide
– Comparison of Key Differences

Key Terms: Alumina, Aluminum Oxide, Amphoteric, Bauxite, Carborundum, Corundum, Electrical Insulator, Silicon Carbide, Sublimation

What is Aluminum Oxide

Aluminum oxide is an inorganic compound having the chemical formula Al₂O₃. This is also known as alumina. The molar mass of this compound is 101.96 g/mol. It is an oxide of aluminum. This compound occurs in nature mainly as corundum or bauxite.

The melting point of aluminum oxide is 2072°C, and the boiling point is 2977°C. The compound appears as a white crystalline powder which is odorless. It is insoluble in water. Aluminum oxide is used as a starting material for smelting aluminum metal. Aluminum oxide can react with acids as well as bases since it has amphoteric properties. In corundum, the chemical structure of aluminum oxide is hexagonal.

Main Difference - Aluminum Oxide vs Silicon Carbide

Figure 1: Active Aluminum Oxide

Alumina is one of the most cost-effective materials that is used in the production of ceramic.

Properties of Aluminum Oxide

Hardness
Good thermal conductivity
High strength and stiffness
Electrical insulation
Insoluble in water
High chemical resistance

Aluminum oxide can exist in different crystalline phases. The most stable form is the hexagonal crystalline structure. This structure is known as the alpha phase of aluminum oxide. It is the strongest structure of alumina.

What is Silicon Carbide

Silicon carbide is an inorganic compound having the chemical formula CSi. It is composed of one carbon atom and a silicon atom per molecule. The molar mass of this compound is 40.10 g/mol. It appears as a yellow to green crystals. Silicon carbide is also known as Carborundum.

The melting point of silicon carbide is 2,830 °C, and it has no boiling point since it sublimes. Sublimation is the phase transition of a substance directly from the solid to the gas phase. Therefore, there is no liquid phase for silicon carbide. The melting point actually refers to the sublimation temperature.

Difference Between Aluminum Oxide and Silicon Carbide

Figure 2: Silicon Carbide

Naturally occurring silicon carbide is found only in minute quantities in corundum deposits. Hence, most silicon carbides used in the world is synthetic. Although it is rare on earth, silicon carbide is common in space as stardust found on carbon-rich stars.

Silicon carbide has a number of crystalline forms. It shows polymorphism. The most common structure among them is alpha silicon carbide form. It has a hexagonal crystal structure. Although silicon carbide has a dark color, pure silicon carbide is colorless. The dark color is a result of the presence of iron impurities and the silicon dioxide layer on the surface of this compound. Silicon carbide is a semi-conductor.

Definition

Aluminum Oxide: Aluminum oxide is an inorganic compound having the chemical formula Al₂O₃.

Silicon Carbide: Silicon carbide is an inorganic compound having the chemical formula CSi.

Molar Mass

Aluminum Oxide: The molar mass of aluminum oxide is 101.96 g/mol.

Silicon Carbide: The molar mass of Silicon carbide is 40.10 g/mol.

Other Names

Aluminum Oxide: Aluminum oxide is also known as alumina.

Silicon Carbide: Silicon carbide is also known as Carborundum.

Electrical Conductivity

Aluminum Oxide: Aluminum oxide is an electrical insulator.

Silicon Carbide: Silicon carbide is a semi-conductor.

Appearance

Aluminum Oxide: Aluminum oxide is a white crystalline powder.

Silicon Carbide: Silicon carbide yellow to green crystals.

Melting and Boiling Point

Aluminum Oxide: The melting point of aluminum oxide is 2072°C, and the boiling point is 2977°C.

Silicon Carbide: The melting point of silicon carbide is 2,830 °C, and it has no boiling point since it sublimes. Thus the melting point is actually the sublimation temperature of silicon carbide.

Conclusion

Both aluminum oxide and silicon carbide are inorganic compounds. Although aluminum oxide is naturally occurring on earth crust, silicon carbide is rarely found. The main difference between aluminum oxide and silicon carbide is that aluminum oxide is an electrical insulator whereas silicon carbide is a semi-conductor.

Image Courtesy:

1. “Active Al2O3” By GOKLuLe 盧樂 – Own work (CC BY-SA 3.0) via Commons Wikimedia
2. “Silicon carbide – mesh 60” By W.carter – Own work (CC0) via Commons Wikimedia

References:

1. “Structure/Chemical Properties.” Aluminum Oxide (Al2O3), Available here.
2. “Alumina.” Encyclopædia Britannica, Encyclopædia Britannica, inc., 26 Jan. 2016, Available here.
3. “Aluminum Oxide, Al2O3 Ceramic Properties.” Aluminum Oxide | Al2O3 Material Properties, Available here.
4. “Silicon carbide.” Encyclopædia Britannica, Encyclopædia Britannica, inc., 28 Aug. 2008, Available here.