MODELING OF DIMENSIONAL CHANGES DURING POLYMER CERAMIC CONVERSION FOR BULK COMPONENT FABRICATION

Shrinkage and porosity generation during conversion of polymer filler systems into ceramic bodies during pyrolysis is examined. In the presence of an inert filler phase such as Si3N4 or SiC powder dispersed in an organosilicon polymeric matrix only porous microstructures may be obtained without any shrinkage. By using an active filler phase such as carbide- or nitride-forming transition metals, however, shrinkage of the polymer matrix may be compensated by appropriate expansion of the filler phase. A model is derived to predict the critical volume fractions of various potential active filler systems in inert and reactive gas atmospheres, which can be effective in controlling shrinkage and porosity during the fabrication of ceramic components from polymer-derived precursor materials.