The characterisation of aluminium hydroxide gels by nitrogen adsorption
| Autor: | G. C. Bye, K. S. W. Sing, J. G. Robinson |
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| Rok vydání: | 2007 |
| Předmět: | |
| Zdroj: | Journal of Applied Chemistry. 17:138-142 |
| ISSN: | 1934-998X 0021-8871 |
| Popis: | Aluminium hydroxide gels with a range of textures have been prepared by the hydrolysis of aluminium s- butoxide with water, aqueous ethanol and aqueous glycerol. Crystallisation was permitted to take place to varying extents by ageing of precipitates in their mother liquors at room temperature. Adsorption isotherms on the outgassed gels were of Types II and IV of the Brunauer classification. An examination of the data by plotting reduced isotherms (V/Vmversus P/Po) revealed the existence of reversible capillary condensation on some of the hydroxides, although the isotherms were of Type II. The Lippens de Boer t method has been found useful in locating the onset of capillary condensation in an adsorption isotherm, but the t-plot can be misleading with samples that have a spread of pore dimensions extending into both the micro- and transitional-pore regions. This situation appears to arise in pseudoboehmites aged for extended periods so that cementation is extensive. The principal factors influencing the texture of the gels appear to be the extent of crystallisation and the amount of inter-particle cementation. Thus amorphous material prepared in water was found to be porous whereas that precipitated in glycerol, which apparently protects the surface of the primary particles, was non-porous (or macro-porous). Transitional pore systems with the best definition were obtained with pseudoboehmites, especially with those formed by ageing in aqueous ethanol. In water, the ready conversion of pseudoboehmite to low-area, non-porous, bayerite is a complicating factor. |
| Databáze: | OpenAIRE |
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