Calcination products of gibbsite studied by X-ray diffraction, XPS and solid-state NMR
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Date
2014-03-20
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Abstract
The changes caused by heat treatment of gibbsite powder at 300–1473 K were studied using the X-ray
diffraction (XRD), X-ray photoemission (XPS) spectra and 27Al magic angle spinning nuclear magnetic
resonance spectroscopy (27Al MAS NMR). XRD analysis indicates that the transformation sequence
involves the formation of κ-Al2O3 as an intermediate phase between χ- and α-Al2O3. The crystallite size
of χ-Al2O3 is as small as 10 nm. XPS analysis indicates that the ratio of aluminium atoms to oxygen atoms
in χ-Al2O3 and κ-Al2O3 increases, whereas the expected ratio is observed in α-Al2O3. The percentage of
AlO4 units in the transition aluminas follows the same behaviour as the ratio of Al/O.