Pore formation in the pyrolysis of polymers to ceramics

Fabrication of a nonoxide ceramic SIC from pyrolysis of a polymer precursor, i.e. poly(carbosilane) was investigated. During pyrolysis the generation of small molecules such as hydrogen and methane results in the formation of pores. A mathematical model was developed to study the nucleation and growth of gas bubbles which lead to such pore formation. The mathematical model has the capability of predicting porosity and its distribution which is influenced by temperature, pressure, as well as the thickness, chemistry, and physical properties of the pyrolyzing object. Thermogravimetric analysis and scanning electron microscopy were used to study the pore formation and possible cracking during pyrolysis. Submicron pores were observed in the thicker fibers. Based on the best estimate of physical properties, the mathematical model is capable of predicting the critical thickness of the pyrolyzing object for which there will be pore formation.