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Aluminum K‐Edge Absorption (XANES) Studies of Noncrystalline Mullite Precursors
Author(s) -
Küper Gerhild,
Peitz Bettina,
Winter Ines,
Hormes Josef,
Schneider Hartmut,
Schmücker Martin,
Voll Dietmar,
Hoffbauer Wilfried
Publication year - 1996
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/j.1151-2916.1996.tb07952.x
Subject(s) - mullite , xanes , crystallization , materials science , silicate , analytical chemistry (journal) , absorption (acoustics) , aluminium , absorption spectroscopy , absorption edge , spectral line , x ray absorption spectroscopy , chemistry , band gap , optics , ceramic , physics , optoelectronics , astronomy , metallurgy , composite material , organic chemistry , chromatography
Noncrystalline aluminum silicate precursors MP1 and MP3 with different ratios of Al in tetrahedral ( [4] A1), pentahedral ( [5] A1), and octahedral ( [6] A1) position were prepared from aluminum sec‐butylate and tetraethoxysilane (Al/Si ratio: 3/1) making use of a slow and rapid hydrolysis process, respectively. The MP2 precursor was synthesized from aluminum sec‐butylate and silicon tetrachloride (Al/Si ratio: 4/1) by rapid hydrolysis. All aluminum silicate gels were heat‐treated to temperatures just prior to crystallization to mullite and γ‐Al 2 O 3 , respectively (MP1 and MP3: 800°C; MP2: 300°C). Al K near‐edge absorption spectra (XANES) of the mullite precursors and of several suitable crystalline reference materials were measured using monochromatic synchrotron radiation. The reference XANES spectra yielded a linear correlation between the energy position of the first inflection point of the white lines and the frequency of sixfold‐coordinated Al ( [6] A1) in the samples. A similar though less straightforward correlation seems to hold also for the white line intensities. From these findings, the actual [61] A1 frequencies for the mullite precursors under investigation were derived to be <10% (MP1), =30% (MP3), and =60% (MP2). The [6] A1 frequency distribution in the mullite precursors displays a trend similar to that determined by 27 A1 NMR spectroscopy.