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), pp. 2290-2297. Wiley, ISSN 00027820,
[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 |
| Journal 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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