DIFFUSION OF DEGRADATION PRODUCTS IN CERAMIC MOLDINGS DURING PYROLYSIS - EFFECT OF GEOMETRY

A general equation applicable to a sphere, an infinite plate, and an i nfinite cylinder is used to calculate the transient diffusion of degra dation product in a ceramic molding during pyrolysis, The solution inc ludes the concentration-dependent diffusion coefficient for diffusion of monomer in its parent polymer which forms the continuous phase in t he ceramic in the as-molded state, In the early stages of pyrolysis, b efore continuous porosity has developed, the model searches for the cr itical heating rate above which defects are produced, Reasonable agree ment is obtained with experimentally measured critical heating rates f or 3-mm-thick plates.