Polymer-Derived Silicon Oxycarbide/Hafnia Ceramic Nanocomposites. Part I: Phase and Microstructure Evolution During the Ceramization Process
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.
Document Type: Research Article
Affiliations: 1: Technische Universität Darmstadt, Institut für Materialwissenschaft, Petersenstrasse 23, D-64287 Darmstadt, Germany 2: Technische Universität Darmstadt, Institut für Angewandte Geowissenschaften, Schnittspahnstrasse 9, D-64287 Darmstadt, Germany 3: Universität Stuttgart, Institut für Physikalische Chemie, Pfaffenwaldring 55, D-70569 Stuttgart, Deutschland, Germany
Publication date: June 1, 2010