ACTIVE-FILLER-CONTROLLED PYROLYSIS OF PRECERAMIC POLYMERS

Manufacturing of bulk ceramic components from materials in the system Si-Me-C-N-O (Me Ti, Cr, V, Mo, Si, B, CrSi2, MoSi2, etc.) from precera mic organosilicon polymers-such as poly(carbosilanes), poly(silazanes) , or poly(siloxanes)-has become possible by incorporating reactive fil ler particles into the liquid or solid polymer precursor. During pyrol ytic decomposition of the polymer matrix, the filler particles react w ith carbon from the polymer precursor or nitrogen from the reaction ga s atmosphere to form new (oxy)carbide or (oxy)nitride phases embedded in a nanocrystalline SI-O-C(-N) matrix. The selective expansion encoun tered in the filler phase reaction can be used to compensate for the p olymer shrinkage upon pyrolytic conversion. The formation of a transie nt pore network between 400 degrees and 1000 degrees C is governed by the polymer decomposition as well as the filler particle reaction kine tics, Thus, the properties of the oxycarbonitride composite materials can be tailored by controlling the microstructures of the polymer-deri ved matrix phase, the filler network, and the residual porosity. Near- net-shape forming of bulk ceramic components, even with complex geomet ry, is possible, making novel applications of polymer-derived bulk mat erials in biomedical, electrical, and mechanical fields highly interes ting.