MASS DIFFUSION-CONTROLLED BUBBLING AND OPTIMUM SCHEDULE OF THERMAL DEGRADATION OF POLYMERIC BINDERS IN MOLDED POWDERS

摘要

During the thermal removal of polymeric binders from molded powder specimens, the gas pressure of the species produced in the thermal degradation of the polymer may exceed the ambient pressure and then bubbling (a defect) occurs. Here the gas-pressure evolution in the early stages of thermal degradation is modeled using experimental degradation kinetics, thermodynamic models for the gas-liquid equilibrium, models for the diffusion coefficient, and the species conservation principle. The predicted results show a strong dependence of the instatantaneous gas-pressure distribution within the specimen on the earlier temperature history and the initial concentration of the volatile product (pre-charge) formed during molding.