Ionescu, Emanuel ; Papendorf, Benjamin ; Kleebe, Hans-Joachim ; Poli, Fabrizia ; Müller, Klaus ; Riedel, Ralf (2010):
Polymer-Derived Silicon Oxycarbide/Hafnia Ceramic Nanocomposites. Part I: Phase and Microstructure Evolution During the Ceramization Process.
In: Journal of the American Ceramic Society, 93 (6), pp. 1774-1782. Wiley, ISSN 0002-7820,
DOI: 10.1111/j.1551-2916.2010.03765.x,
[Article]

Abstract

Polymer-derived SiOC/HfO2 ceramic nanocomposites were prepared via chemical modification of a commercially available polysilsesquioxane by hafnium tetra (n-butoxide). The ceramization process of the starting materials was investigated using thermal analysis and in situ Fourier-transformed infrared spectroscopy and mass spectrometry. Furthermore, solid-state NMR, elemental analysis, powder X-ray diffraction, and electron microscopy investigations were performed on ceramic materials pyrolyzed at different temperatures ranging from 800° to 1300°C, in order to obtain information about the structural changes and phase evolution thereof. The hafnium alkoxide-modified precursor was shown to convert into an amorphous single-phase SixHfyOzCw ceramic at temperatures up to 800°C. By increasing the temperature to 1000°C, amorphous hafnia begins to precipitate throughout the silicon oxycarbide matrix; thus, monodisperse hafnia particles with a diameter of <5 nm are present in the ceramic, indicating a homogeneous nucleation of HfO2. At temperatures ranging from 1100° to 1300°C, crystallization of the hafnia nanoprecipitates as well as phase separation of the SiOC matrix occur. The chemical modification of the preceramic precursor with hafnium alkoxide can be considered as a promising method for the preparation of SiOC/HfO2 nanocomposites with well-dispersed hafnia nanoparticles.

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