Evolution of crystalline aluminates from hybrid gel-derived precursors studied by XRD and multinuclear solid state MAS NMR IV: Calcium dialuminate, CaAl4O7 and calcium hexaluminate, CaAl12O19
UNSPECIFIED. (2000) Evolution of crystalline aluminates from hybrid gel-derived precursors studied by XRD and multinuclear solid state MAS NMR IV: Calcium dialuminate, CaAl4O7 and calcium hexaluminate, CaAl12O19. THERMOCHIMICA ACTA, 363 (1-2). pp. 181-188. ISSN 0040-6031Full text not available from this repository.
X-ray amorphous calcium aluminate gels of dialuminate and hexaluminate composition were prepared, the former by two methods, and their thermal crystallisation was monitored by thermal analysis, X-ray powder diffraction and Al-27 MAS NMR. Both gel compositions lose a large amount of solvent and organic by-products below 600 degreesC, forming amorphous precursors with Al-27 NMR spectra containing resonances corresponding to tetrahedral and octahedral sites, and another site with a peak at 36-39 ppm. The dialuminate gel crystallises abruptly at 900 degreesC to the essentially phase-purr compound containing Al predominantly in two distorted tetrahedral environments. The hexaluminate gel crystallises exothermically at 900 degreesC to gamma -alumina spinel, containing only tetrahedral and octahedral Al. The magnetoplumbite structure of the hexaluminate phase appears in an exothermic reaction at 1160 degreesC, this phase-pure reaction product containing Al atoms in one tetrahedral and two distinguishable octahedral sites. The first Ca-43 MAS NMR spectra of the crystalline dialuminate and hexaluminate are also reported. (C) 2000 Elsevier Science B,V. All rights reserved.
|Item Type:||Journal Article|
|Subjects:||Q Science > QD Chemistry|
|Journal or Publication Title:||THERMOCHIMICA ACTA|
|Publisher:||ELSEVIER SCIENCE BV|
|Official Date:||27 November 2000|
|Number of Pages:||8|
|Page Range:||pp. 181-188|
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