Dehydration process and structural development of cordierite ceramic precursors derived from FTIR spectroscopic investigations
- Autor(en)
- Dietmar Voll, Anton Beran
- Abstrakt
Cordierite precursors were prepared by a solgel process using tetraethoxysilane, aluminum sec.-butoxide, and Mg metal flakes as starting materials. The precursors were treated by 15-h heating steps in intervals of 100 °C from 200 to 900 °C; they show a continuous decrease in the analytical water content with increasing preheating temperatures. The presence of H2O and (Si,Al)-OH combination modes in the FTIR powder spectra prove the presence of both H2O molecules and OH groups as structural components, with invariable OH concentrations up to preheating temperatures of 500 °C. The deconvolution of the absorptions in the (H2O,OH)-stretching vibrational region into four bands centred at 3584, 3415, 3216 and 3047 cm-1 reveals nonbridging and bridging H2O molecules and OH groups. The precursor powders remain X-ray amorphous up to preheating temperatures of 800 °C. Above this temperature the precursors crystallize to œ-cordierite; at 1000 °C the structure transforms to a-cordierite. Close similarities exist in the pattern of the 1400-400 cm-1 lattice vibrational region for precursors preheated up to 600 °C. Striking differences are evident at preheating temperatures of 800 °C, where the spectrum of the precursor powder corresponds to that of conventional cordierite glass. Bands centred in the "as-prepared" precursor at 1137 and 1020 cm-1 are assigned to Si-O-stretching vibrations. A weak absorption at 872 cm-1 is assigned to stretching modes of AlO4 tetrahedral units and the same assignment holds for a band at 783 cm-1 which appears in precursors preheated at 600 °C. With increasing temperatures, these bands show a significant shift to higher wavenumbers and the Al-O stretching modes display a strong increase in their intensities. (Si,Al)-O-(Si,Al)-bending modes occur at 710 cm-1 and the band at 572 cm-1 is assigned to stretching vibrations of AlO6 octahedral units. A strong band around 440 cm-1 is essentially attributed to Mg-O-stretching vibrations. The strongly increasing intensity of the 872 and 783 cm-1 bands demonstrates a clear preference of Al for a fourfold-coordinated structural position in the precursors preheated at high temperatures. The observed band shift is a strong indication for increasing tetrahedral network condensation along with changes in the Si-O and Al-O distances to tetrahedra dimensions similar to those occurring in crystalline cordierite. These structural changes are correlated to the dehydration process starting essentially above 500 °C, clearly demonstrating the inhibiting role of H2O molecules and especially of OH groups.
- Organisation(en)
- Institut für Mineralogie und Kristallographie
- Externe Organisation(en)
- Universität Wien
- Journal
- Physics and Chemistry of Minerals
- Band
- 29
- Seiten
- 544-551
- Anzahl der Seiten
- 8
- ISSN
- 0342-1791
- Publikationsdatum
- 2002
- Peer-reviewed
- Ja
- ÖFOS 2012
- 1051 Geologie, Mineralogie
- Link zum Portal
- https://ucrisportal.univie.ac.at/de/publications/07d95c45-900e-46f3-8ea8-b230ea491d09