Summary
Changes in specific surface area, interpreted in conjunction withX-ray powder diffraction and electron microscopy, have been used to follow the formation of pseudoboehmite and bayerite from amorphous aluminium hydroxide. Precipitates, essentially free from foreign ions, were prepared by the hydrolysis of aluminium s-butoxide and ageing in water, aqueous ethanol and aqueous glycerol was studied. A comparison of rates of crystallization in these media provides evidence for the idea that pseudoboehmite is formed by an inter- and intra-particle condensation involving hydroxyl groups while bayerite is formed by a dissolution and recrystallization process. Possible rate determining factors in these mechanisms are considered and the role of particle aggregation-cementation, the degree of which depends on the nature of the solvent, is discussed.
Zusammenfassung
Änderungen in der spezifischen Oberfläche interpretiert in Verbindung mit Röntgenbeugung und elektronenmikroskopischen Aufnahmen wurden angewendet, um die Bildung von Pseudoböhmit und Bayerit aus amorphem Aluminiumhydroxid zu verfolgen. Die ausgefällten Produkte, im wesentlichen frei von Fremdionen, wurden durch Hydrolyse von Aluminium-s-butoxid und Alterung in Wasser, wäßrigem Äthanol und wäßrigem Glycerin untersucht. Ein Vergleich der Kristallisationsgeschwindigkeiten in diesen Medien legt nahe, daß Pseudoböhmit durch eine inter- und intra-Teilchenkondensation durch Hydroxylgruppen gebildet wird, während Bayerit durch Lösungs-und Rekristallisationsprozesse entsteht. Mögliche geschwindigkeitsbestimmende Faktoren dieser Mechanismen werden betrachtet, und die Rolle der Partikel-verklebung, deren Ausmaß von der Natur des Lösungsmittels abhängt, wird diskutiert.
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Bye, G.C., Robinson, J.G. Crystallization processes in aluminium hydroxide gels. Kolloid-Z.u.Z.Polymere 198, 53–60 (1964). https://doi.org/10.1007/BF01499454
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DOI: https://doi.org/10.1007/BF01499454