Polymer-Derived Silicon Oxycarbide/Hafnia Ceramic Nanocomposites. Part II: Stability Toward Decomposition and Microstructure Evolution at T≫1000°C
Abstract:This study presents first investigations on the high-temperature stability and microstructure evolution of SiOC/HfO2 ceramic nanocomposites. Polymer-derived SiOC/HfO2 ceramic nanocomposites have been prepared via chemical modification of a commercially available polysilsesquioxane by hafnium tetra (n-butoxide). The modified polysilsesquioxane-based materials were cross-linked and subsequently pyrolyzed at 1100°C in argon atmosphere to obtain SiOC/HfO2 ceramic nanocomposites. Annealing experiments at temperatures between 1300° and 1600°C were performed and the annealed materials were investigated with respect to chemical composition and microstructure. The ceramic nanocomposites presented here were found to exhibit a remarkably improved thermal stability up to 1600°C in comparison with hafnia-free silicon oxycarbide. Chemical analysis, X-ray diffraction, FTIR, and Raman spectroscopy as well as electron microscopy (SEM, TEM) studies revealed that the excellent thermal stability of the SiOC/HfO2 nanocomposites is a consequence of the in situ formation of hafnon (HfSiO4), which represents a concurrent reaction to the carbothermal decomposition of the SiOC matrix. Thus, by the annealing of SiOC/HfO2 materials at 1600°C, novel HfSiO4/SiC/C ceramic nanocomposites can be generated. The results presented emphasize the potential of these materials for application at high temperatures.
Document Type: Research Article
Affiliations: 1: Technische Universität Darmstadt, Institut für Materialwissenschaft, D-64287 Darmstadt, Germany 2: Technische Universität Darmstadt, Institut für Angewandte Geowissenschaften, D-74287 Darmstadt, Germany
Publication date: June 1, 2010