| Autor: |
Don Seykens, J. Ben H. Jansen, Roland J. M. J. Vogels, Paul A. Buining, John W. Geus, J. Theo Kloprogge |
| Rok vydání: |
1995 |
| Předmět: |
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| Zdroj: |
Journal of Non-Crystalline Solids. 191:38-44 |
| ISSN: |
0022-3093 |
| Popis: |
The aging of the aluminum tridecamer in acidified aluminum sec-butoxide is studied with 27Al nuclear magnetic resonance. At 20°C the tridecamer content passes through a maximum of 19.7% after 133 h of aging to decline subsequently to a final content of approximately 12%. At 90°C the tridecamer disappears within 21 h of aging due to clustering. After 91 h colloidal gibbsite forms, while the pH drops continuously from 4.3 to 3.5. Simultaneously the monomer concentration increases to approximately 6.6%. The increase is possibly due to liberation of the central fourfold-coordinated Al from the tridecamer that rearranges to hexameric rings, and to dissolution of some gibbsite in the acid solution. The hexameric rings are considered to be the precursor for the crystallization of gibbsite and boehmite. Increase of the preparation temperature from 20°C to 80°C has no effect on the amount of tridecamer, although at 90°C the amount increases from approximately 9% to 14.1%. An increase of the preparation temperature leads to changes in the second-order quadrupole effects, which results in a line sharpening from 19.5 to 9.8 Hz for the central fourfold-coordinated Al signal of the tridecamer at 63.3 ppm. © 1995 Elsevier Science B.V. All rights reserved. |
| Databáze: |
OpenAIRE |
| Externí odkaz: |
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Full Text from ScienceDirect