Polymer-derived porous ceramics from novel silicon-based preceramic/sucrose systems

Porous Si/C/O/(N) ceramic bodies were developed by the direct consolidation of novel liquid silicon-based preceramic polymer/porogen (methacryloxypropyl silsesquioxane/sucrose) systems, burnout, and N-2 pyrolysis (1300-1500. degrees C), and they were characterized via open porosity, volumetric shrinkage, and mass loss measurements. The evolution of phases as temperature increased was analyzed using XRD, TGA-mass spectrometry tests, and Si-29 NMR. The free carbon phase was characterized via Raman spectroscopy, and its content was determined using a carbon analyzer. Porous microstructures were analyzed by SEM/EDS and Hg-porosimetry, and by measuring the N-2 adsorption/desorption and specific surface area. The final ceramics exhibited a hierarchical porosity composed of large irregular pores that grew with temperature, together with a lower volume of meso- and micropores. ss-SiC whiskers and faceted hexagonal crystals of alpha-Si3N4 were observed inside of cavities. The presence of meso- and micropores explained the high specific surface area achieved in the material pyrolyzed at 1500 degrees C.