Thermo-Oxidative Stability of Polymer-Derived Si-B-C Ceramics

Si-B-C ceramics with different elemental compositions and microstructures were prepared by the pyrolysis of an o-carborane-containing poly(silylene-arylacetylene) (CB-PSA) thermoset at 1000 degrees C, 1200 degrees C, 1300 degrees C, and 1450 degrees C. The thermo-oxidative stability of the ceramics was investigated by tracing the weight loss of ceramics during the isothermal oxidation at 800 degrees C, 1000 degrees C, and 1200 degrees C under dry oxygen. The chemical bonding states of the ceramics before oxidation and the elemental compositions of the ceramics after oxidation were analyzed by X-ray photoelectron spectroscopy (XPS). The surface morphologies of the ceramics after oxidation were recorded using scanning electron microscopy (SEM). The results show that the Si-B-C ceramic prepared at 1450 degrees C produces an integral borosilicate film on the surface of the ceramics when oxidized at both 1000 degrees C and 1200 degrees C and exhibits better oxidation resistance than the other Si-B-C ceramics prepared at 1000 degrees C, 1200 degrees C, and 1300 degrees C. Oxidation temperatures, elemental compositions, and crystallites of the Si-B-C ceramics are found to influence the formation of the borosilicate films which plays an important role in the thermo-oxidative stability of the ceramics.