Development of Dense Filler-Free Polymer-Derived SiOC Ceramics by Field-Assisted Sintering

Large samples of dense polymer-derived ceramics in an Si-O-C system were prepared without using any filler particles or catalysts. For this purpose a commercial polymethylsilsesquioxane powder was first pyrolyzed at 900 degrees C and then rapidly hot-pressed at temperatures between 1400 degrees and 1600 degrees C. Density, hardness, and flexural strength of the samples were measured as a function of hot-pressing temperature. No carbothermic reaction between SiO2 and C was observed, but nanocrystals of beta-SiC were found in all the samples referring to a phase separation of the originally amorphous microstructure.