Aluminum oxide is a common building block in electronics. It is widely used as a metal for making wires in semiconductor chips and transistors because of its low cost and good electrical conductivity.
why does aluminium oxide conduct electricity when molten?
Generally speaking, metals are good conductors because they have free electrons. Those electrons are dislocated from the rest of the atom and can be transported to electrodes where they can be discharged as current.
However, a number of oxides have different properties. These vary according to the nature of the bonds involved, ion sizes and charge ratios.
Lithium oxide, for example, has very high specific conductivity because its ions are relatively small and arranged in close-packed structures. On the other hand, magnesium oxide does not have this particular property because its ions are much larger and more complex.
In this case, the reason that molten aluminium oxide has higher specific conductivity than magnesium oxide is because the difference in electronegativity between the metal and the oxygen is lower. This means that the bond between the metal and the oxygen will be more ionic rather than covalent, which in turn will increase its conductivity.
Consequently, designing processes for low energy smelting requires an accurate knowledge of not only the total conductivity but also the partial conductivity of molten alumina as a function of temperature and composition. Unfortunately, experimental data on this behavior are quite scarce for many of the molten oxides.