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Decomposition-Coarsening Model of SiOC/HfO2 Ceramic Nanocomposites Upon Isothermal Anneal at 1300°C

Kleebe, Hans-Joachim and Nonnenmacher, Katharina and Ionescu, Emanuel and Riedel, Ralf and Soraru, G. D. (2012):
Decomposition-Coarsening Model of SiOC/HfO2 Ceramic Nanocomposites Upon Isothermal Anneal at 1300°C.
In: Journal of the American Ceramic Society, 95 (7), Wiley, pp. 2290-2297, ISSN 00027820,
[Online-Edition: http://dx.doi.org/10.1111/j.1551-2916.2012.05227.x],
[Article]

Abstract

Pronounced variations of the crystallite size of hafnia (HfO2) precipitates in silicon oxycarbide (SiOC)–HfO2 ceramic nanocomposites were studied by TEM upon annealing bulk samples at 1300°C for times ranging from 1 to 200 h. TEM investigations revealed homogeneous nucleation and crystallization of hafnia in the amorphous, Hf-bearing SiOC matrix upon pyrolysis at 1300°C. Unexpectedly, high-temperature anneal resulted in a pronounced coarsening of the hafnia crystallites at internal surfaces, due to a decrease of the C content at surface-near regions. Based on the crystallite size, the diffusion coefficient of Hf was calculated via the Lifshitz-Slyozov-Wagner (LSW) theory for Ostwald ripening for both the bulk and internal surface regions. The diffusion coefficient of hafnium, DHf, in the C-depleted surface areas was 10−18 m2/s, whereas DHf of the SiOC bulk was three orders of magnitude lower with 10−21 m²/s. The present work underlines that the polymer-derived ceramics are in fact prone to phase separation and local chemical changes upon high-temperature treatment and are not as stable as commonly considered.

Item Type: Article
Erschienen: 2012
Creators: Kleebe, Hans-Joachim and Nonnenmacher, Katharina and Ionescu, Emanuel and Riedel, Ralf and Soraru, G. D.
Title: Decomposition-Coarsening Model of SiOC/HfO2 Ceramic Nanocomposites Upon Isothermal Anneal at 1300°C
Language: English
Abstract:

Pronounced variations of the crystallite size of hafnia (HfO2) precipitates in silicon oxycarbide (SiOC)–HfO2 ceramic nanocomposites were studied by TEM upon annealing bulk samples at 1300°C for times ranging from 1 to 200 h. TEM investigations revealed homogeneous nucleation and crystallization of hafnia in the amorphous, Hf-bearing SiOC matrix upon pyrolysis at 1300°C. Unexpectedly, high-temperature anneal resulted in a pronounced coarsening of the hafnia crystallites at internal surfaces, due to a decrease of the C content at surface-near regions. Based on the crystallite size, the diffusion coefficient of Hf was calculated via the Lifshitz-Slyozov-Wagner (LSW) theory for Ostwald ripening for both the bulk and internal surface regions. The diffusion coefficient of hafnium, DHf, in the C-depleted surface areas was 10−18 m2/s, whereas DHf of the SiOC bulk was three orders of magnitude lower with 10−21 m²/s. The present work underlines that the polymer-derived ceramics are in fact prone to phase separation and local chemical changes upon high-temperature treatment and are not as stable as commonly considered.

Journal or Publication Title: Journal of the American Ceramic Society
Volume: 95
Number: 7
Publisher: Wiley
Divisions: 11 Department of Materials and Earth Sciences > Earth Science > Geo-Material-Science
11 Department of Materials and Earth Sciences > Material Science > Dispersive Solids
11 Department of Materials and Earth Sciences > Earth Science
11 Department of Materials and Earth Sciences > Material Science
11 Department of Materials and Earth Sciences
Date Deposited: 21 Mar 2013 09:00
Official URL: http://dx.doi.org/10.1111/j.1551-2916.2012.05227.x
Identification Number: doi:10.1111/j.1551-2916.2012.05227.x
Funders: The research was funded by the Deutsche Forschungsgemeinschaft (DFG) (Priority Program SPP 1181), and by the Ministry of Higher Education, Research and Arts in Hesse, Germany (Excellence Center AdRIA: Adaptronik – Research, Innovation, Application).
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