Alumina is commonly termed as aluminum oxide which synthetically produces aluminum oxide. It is a chemical compound comprising of oxygen and aluminum. It is a colorless crystalline substance that is found naturally in the variety of forms namely sapphire and ruby. They are mostly used in a production of aluminum metal.


Aluminum Oxide is composed of bauxite. It is an aluminum oxide that is mixed with other elements and oxides of iron and silicon. It also comprises of clay. So bauxite can either be soft or hard as that of a rock. They are characterized with pink, white, red or combination of these.

Structure of Alumina

Aluminum Oxide occurs in several other forms. Among them the most common and naturally occurring crystalline form of alumina is Corundum. Example: Rubies and Sapphire. Rubies are dark red in color and sapphire consists of the particular amount of impurities namely titanium and iron are of different colors.

Oxygen atom forms a slightly distorted hexagonal slight packing in the lattice of corundum. It is found as a mineral in gneisses and some other marbles. They are also found in nepheline syenite intrusives.

Properties of Alumina

  • Alumina possesses good thermal conductivity. At elevated temperature, it can withstand alkali attacks and a strong acid.
  • It consists of excellent dielectric properties. It is a wear resistant.
  • Metallic Aluminium is highly reactive with atmospheric oxygen.
  • It exhibits high stiffness and strength.
  • It is available at a purity range from 94%.

Applications of Aluminium Oxides

  • They are widely used in Electronic Substrates, Thread and Wire Guides, Seal Rings, Ballistic armor, Thermometry Sensors, Grinding Media, Furnace Liner Tubes, High Voltage Insulators, Laboratory Instrumentary Tubes.
  • Various formulation of glass consists of aluminum oxide as an ingredient. It is used in purification that is the removal of water from gas streams. They are employed in high-performance applications.
  • It is a favored filler for plastic. It is sometimes present in cosmetics such as nail polish, lipstick and blush.
  • They are broadly used as an abrasive. Various sandpaper makes use of aluminum oxide crystals.
  • They are employed in the manufacturing of titles where they are attached inside the pulverized fuel lines to protect high wearing areas.

Practise This Question

A bulb and a capacitor are connected in series to a source of alternating current. If its frequency is increased, while keeping the voltage of the source constant, then