why does aluminium oxide have a high melting point?
Aluminum has a very high melting point when compared to other metals like copper, iron and brass. In its pure form, it melts at approximately 660 degrees Celsius or 1220 degrees Fahrenheit.
The reason for this is that the bond between the aluminium and oxygen in molten aluminium oxide is not a purely ionic bond but a complex one. That means that there is a higher electronegativity difference between the two elements and that it is easier to force oxygen to give its electrons back to aluminium by using an electric potential.
This is one of the reasons that aluminum oxide is used as a chemically inert filler for bricks, plastics and heavy clayware. It is also an abrasive material that is used in sandpaper and as a replacement for industrial diamonds.
Aluminium oxide is also a good ceramic material that has many important applications in the manufacture of adsorbents and catalysts. It has excellent resistance to both acid and alkali substances and is also very hard and wear-resistant.
In addition, aluminium oxide has a good electrical conductivity for a ceramic material (30Wm-1K-130Wm-1K-1). This is why it is used as an insulator in power electronics.
In order to produce a small pool of molten aluminium, it must be heated until it reaches a temperature where the aluminium can ignite and burn. This is done by placing the molten aluminium in contact with a small quantity of water and steam at a temperature of over 660 degrees Celsius. The water and steam tend to vaporise quickly and this creates a reaction with the aluminium which subsequently causes it to burn.