Ultraporous monoliths of alumina prepared at room temperature by aluminium oxidation

The oxidation of aluminium through a mercury film usually leads to unorganized filaments or fibrous powders of hydrated alumina. Here, we show that the addition of a small amount of silver in the mercury considerably modifies the growth process, and that large sized monoliths can be obtained through a new process. Regular growth can be maintained at a typical rate of 2.1 μm s−1 (∼0.75 cm/h) for several hours. The samples consist of tangled nanometric fibres and have an open porosity of 99%. The influence of various parameters has been studied and optimal conditions for regular growth have been determined. Anhydrous alumina monoliths with a nanometric microstructure and a high-specific area are obtained after thermal treatments that remove water.