Al 2 O 3 is an electrical insulator but has a relatively high thermal conductivity (30 Wm−1K−1) for a ceramic material. Aluminium oxide is insoluble in water.

It is an amphoteric substance, which reacts with both acids and bases. It occurs as solid and appears white. It is odourless and insoluble in water.

Aluminum oxide is a white odorless crystalline powder. Water insoluble.

So, aluminium oxide is an ionic compound. Still, it is insoluble in water.

The most abundant aluminum compounds are aluminum oxide and aluminum hydroxide, and these are water insoluble. Aluminum oxide may be present in water both in alkalic form (2Al 2 O 3 (s) + 6H + (aq) -> Al 3+ (aq) + 3H 2 O (l)) and in acidic form (2Al 2 O 3 (s) + 2OH - (aq) -> AlO 2- (aq) + H 2 O (l)).