The activation of alumina

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Abstract
An investigation has been made of the physical transformations with occur when γ aluminium trihydrate (gibbsite) is dehydrated by heat treatment, and the effect such transformations have on the adsorption activity and porosity of the material. Dehydration proceeds according to the scheme: trihydrate → monohydrate → alumina, no dihydrate being formed. Between 225° and 500° positions of equilibrium are established between the monohydrate and alumina and the adsorption activity is directly related to the degree of conversion to γ alumina. At 500° and higher temperatures, the material is converted wholly to γ alumina. This, unlike the tri‐ and monohydrates cannot be completely defined as it is a transitional product in a heat‐controlled solid reaction, its state being at first highly disordered but rearranging to an orderly state as the reaction proceeds. The adsorption activity of the material is directly related to the state of disorder. The particle size distribution of the material is unaffected by the heat treatment which it receives, hence the porosity of the final product can be controlled by selection of the starting material. Aluminas covering a wide range of activities can be prepared by simple heat treatment of the hydrate.

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