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/HfO 2 ceramic nanocomposites. Polymer‐derived SiOC/HfO 2 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/HfO 2 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/HfO 2 nanocomposites is a consequence of the in situ formation of hafnon (HfSiO 4 ), which represents a concurrent reaction to the carbothermal decomposition of the SiOC matrix. Thus, by the annealing of SiOC/HfO 2 materials at 1600°C, novel HfSiO 4 /SiC/C ceramic nanocomposites can be generated. The results presented emphasize the potential of these materials for application at high temperatures.