Ablation resistance of precursor derived Si-Hf-C-N(O) ceramics

Polymer derived Si-Hf-C-N(O) foams were produced by the pyrolysis of polysilazane containing varying amounts of hafnium tetra n-butoxide. X-ray tomography was used to determine the cell size distribution. The ablation resistance of the foams was studied by subjecting it to different oxyacetylene flame temperatures. After ablation, fragmentation was not observed and the mass ablation rate was found to be minimal for the foams produced from highest vol% of hafnium tetra n-butoxide. The foams remained X-ray amorphous after ablation and the presence of HfO and SiO bonds were confirmed using ATR spectroscopy. For comparison, a reasonably dense spark plasma sintered pellet was also ablated and the evolution of monoclinic hafnia was confirmed using X-ray diffraction. The microstructural characterization exhibited three different zones on the ablated surface for sintered sample and the ablation mechanisms were understood using thermodynamic calculations.