An-Najah Staff

 A general equation applicable to a sphere, an infinite plate, and an infinite cylinder is used to calculate the transient diffusion of degradation product in a ceramic molding during pyrolysis. The solution includes the concentration-dependent diffusion coefficient for diffusion of monomer in its parent polymer which forms the continuous phase in the ceramic in the as-molded state. In the early stages of pyrolysis, before continuous porosity has developed, the model searches for the critical heating rate above which defects are produced. Reasonable agreement is obtained with experimentally measured critical heating rates for 3-mm-thick plates.