Al2O3nH2O

Al2O3nH2O is a general way to denote hydrated forms of aluminum oxide, consisting of aluminum oxide with water molecules incorporated into the solid structure or present as hydroxyl groups. The exact composition varies with preparation method and conditions, so the value of n can range from zero (anhydrous Al2O3) to several depending on the hydration level. As a result, Al2O3nH2O represents a family of aluminum oxide hydrates rather than a single fixed compound.

Several well-known hydrated aluminum oxides are described by this family. Boehmite, with the formula AlO(OH), and diaspore, AlOOH, are often treated as aluminum oxide hydrates and can be viewed as derived from Al2O3·H2O in the sense of containing oxide and hydroxide components. Aluminum hydroxide, Al(OH)3, is another common hydrated form encountered in precipitation and gels. In practice, commercial and scientific references may write these materials as Al2O3·nH2O to emphasize their relationship to alumina and their varying hydration state.

Properties and transformations of Al2O3nH2O depend on temperature, pH, and history of processing. Upon heating (calcination), hydrated forms lose water and convert to anhydrous or crystalline alumina (Al2O3) through intermediate phases such as hydrated aluminas and gamma- or other polymorphs of alumina. The hydrated forms are typically amorphous or poorly crystalline and can act as precursors in the synthesis of catalysts, adsorbents, and ceramic materials. They also appear in water treatment contexts as precursors to alumina-based flocculants and sensible desiccants.

Overall, Al2O3nH2O describes a versatile family of aluminum oxide hydrates with widespread industrial relevance as precursors to alumina and as functional materials in catalysis, adsorption, and polishing applications.