Oxidation of Polymer-Derived HfSiCNO up to 1600℃

摘要

Oxidation behavior of HfSiCNO ceramics for Hf/Si ratio of 0.09 at 1400℃-1600℃ in ambient air is reported. Quantitative X-ray analysis of oxidized powders shows crystallization of the amorphous phase into tetragonal hafnia, hafnon, and cristobalite (carbides, seen in inert atmosphere heat treatments are absent). Cross-sectional SEM shows the oxide overgrowth on the particles to contain precipitates of hafnia/ hafnon, while the interior of the particles is decorated with nanoscale grains of hafnia in a necklace-like formation. The oxidation kinetics of these materials, determined both from weight-change measurements and from direct observation of oxide overgrowth, are shown to be comparable to the oxidation of SiC single crystals. Oxidation of SiC-SiC minicomposites (straight fiber bundles infiltrated with a SiC matrix), coated with thin films of HfSiCNO prepared by dip-coating was studied. The overgrowth thicknesses for oxidation time of 1000 h at 1600℃ are compared for uncoated, SiCN(O)-coated, and HfSiCNO-coated minicomposites.