Formation of iron-doped mullite (Al 4+2 xSi 2−2 xO 10− x) by temperature- and time-resolved X-ray powder diffraction and EXAFS, and by 27Al MAS NMR spectroscopy

• Published in: Polyhedron 1999-02, Vol.18 (7), p.1083-1087
• Main Authors: Berry, Frank J, Bilsborrow, Robert L, Dent, Andrew J, Mortimer, Michael, Ponton, Clive B, Purser, Beatrice J, Whittle, Karl R
• Format: Article
• Language: English
• Subjects: Combined XRD/EXAFS; MAS NMR; Mullite
• ISSN: 0277-5387
• DOI: 10.1016/S0277-5387(98)00398-2

Temperature- and time-resolved X-ray powder diffraction and Fe K-edge EXAFS have been recorded simultaneously using synchrotron radiation during the calcination of a gel prepared by hydrothermally processing a mixture of aluminium-, silicon- and iron-acetates. The results, which are supported by 27Al MAS NMR studies, show that iron is initially accommodated in the octahedral sites of a poorly crystalline pseudoboehmite-type structure (γ-AlOOH· n H 2O). At ca. 400°C the material becomes amorphous and a small particle highly defective γ-Al 2O 3-type structure develops as the temperature is increased. No evidence for a discrete crystalline silicon-containing phase is observed. The first evidence of the formation of mullite (Al 2 oct (Al 2+2 x tet Si 2−2 x tet ) O 10− x ) in which iron is accommodated in the octahedral sites is observed on reaching 1050°C. The phase develops as a function of time at this temperature.