Synthesis and structural characterization of non-crystalline mullite precursors

verfasst von: H. Schneider, D. Voll, B. Saruhan, J. Sanz, G. Schrader, C. Rüscher, A. Mosset
Abstract: Two different types of non-crystalline mullite precursor with identical bulk composition (72 wt% Al₂O₃, 28 wt% SiO₂) were prepared from tetraethoxysilane and silicon chloride, respectively, and aluminium sec-butozide, by using different methods of hydrolysis. The precursors, designated as type I and III, display different crystallization processes above ≈ 900°C: type I precursors directly form mullite, while type III precursors yield crystallization of transient γ-alumina. Infrared (IR) spectroscopy, large angle X-ray scattering (LAXS) and ²⁷Al nuclear magnetic resonance spectroscopic studies, and ²⁹Si nuclear magnetic resonance (NMR) literature data give evidence for a high degree of structural mixing in type I precursors and for a beginning of segregation into Al₂O₃-rich domains in type III precursors prior to crystallization (≤ 900°C). Both precursors are composed of (SiO) tetrahedra and of (AlO) octahedra, tetrahedra and pentahedra although pentahedra are dominant in type I while octahedra occur more frequently in type III precursors. The driving force for mullitization (type I) and γ-alumina formation (type III) taking place at the same temperature is believed to be the instability of pentahedrally coordinated Al above ≈ 900°C. The sudden disappearance of Al pentahedra probably depends on the formation of reactive network centers during dehydroxylation. This hypothesis is derived from the observation that dehydroxylation and condensation strongly take place in a similar temperature range prior to crystallization.
Organisationseinheit(en): Institut für Mineralogie
Externe Organisation(en): Deutsches Zentrum für Luft- und Raumfahrt e.V. (DLR)
Spanish National Research Council (CSIC)
CEMES Centre d'Elaboration de Materiaux et d'Etudes Structurales
Typ: Artikel
Journal: Journal of non-crystalline solids
Band: 178
Seiten: 262-271
Anzahl der Seiten: 10
ISSN: 0022-3093
Publikationsdatum: 03.11.1994
Publikationsstatus: Veröffentlicht
Peer-reviewed: Ja
ASJC Scopus Sachgebiete: Elektronische, optische und magnetische Materialien, Keramische und Verbundwerkstoffe, Physik der kondensierten Materie, Werkstoffchemie
Elektronische Version(en): https://doi.org/10.1016/0022-3093(94)90295-X (Zugang: Geschlossen)

BibTeX

@article{43d294807bbc41a497ac016ebd6fc04a,
title = "Synthesis and structural characterization of non-crystalline mullite precursors",
abstract = "Two different types of non-crystalline mullite precursor with identical bulk composition (72 wt% Al2O3, 28 wt% SiO2) were prepared from tetraethoxysilane and silicon chloride, respectively, and aluminium sec-butozide, by using different methods of hydrolysis. The precursors, designated as type I and III, display different crystallization processes above ≈ 900°C: type I precursors directly form mullite, while type III precursors yield crystallization of transient γ-alumina. Infrared (IR) spectroscopy, large angle X-ray scattering (LAXS) and 27Al nuclear magnetic resonance spectroscopic studies, and 29Si nuclear magnetic resonance (NMR) literature data give evidence for a high degree of structural mixing in type I precursors and for a beginning of segregation into Al2O3-rich domains in type III precursors prior to crystallization (≤ 900°C). Both precursors are composed of (SiO) tetrahedra and of (AlO) octahedra, tetrahedra and pentahedra although pentahedra are dominant in type I while octahedra occur more frequently in type III precursors. The driving force for mullitization (type I) and γ-alumina formation (type III) taking place at the same temperature is believed to be the instability of pentahedrally coordinated Al above ≈ 900°C. The sudden disappearance of Al pentahedra probably depends on the formation of reactive network centers during dehydroxylation. This hypothesis is derived from the observation that dehydroxylation and condensation strongly take place in a similar temperature range prior to crystallization.",
author = "H. Schneider and D. Voll and B. Saruhan and J. Sanz and G. Schrader and C. R{\"u}scher and A. Mosset",
note = "Funding Information: The authors wish to express their gratitude to Dr T. Rymon-Lipinski for carrying out the DTA studies. Thanks are also due to Dr S.H. Risbud for providing roller-quenched melt glasses. H.S. acknowledges the financial support of the Deutsche Forschungsgemeinschaft (DFG, Bonn, Germany).",
year = "1994",
month = nov,
day = "3",
doi = "10.1016/0022-3093(94)90295-X",
language = "English",
volume = "178",
pages = "262--271",
journal = "Journal of non-crystalline solids",
issn = "0022-3093",
publisher = "Elsevier",
number = "C",
}