A diffusion-controlled kinetic model for binder burnout in a powder compact

Abstract

Many powder metallurgy processes involve the use of a polymeric binder as a carrier for easy manufacture of product pre-forms. Complete and clean removal of the binder before consolidation or firing is essential to achieve high quality materials or products. A diffusion-controlled numerical model was established here for the prediction of binder burnout kinetics within powder compacts. It considers the degradation of a polymeric binder into a monomer, liquid state diffusion of the monomer in a core region, and gaseous transport of the monomer in a gas-filled annulus. The rate-controlling mechanism is identified as the diffusion of the monomer in the liquid core, while gaseous transport in the porous annulus poses minor influence. The model is able to predict the remaining weight fraction of polymer during debinding and the total burnout time under different geometric and processing conditions. It is noted that the burnout time increases markedly with compact size, but varies insignificantly with powder particle size. The rate of binder removal increases sharply with temperature. The theoretical predictions of the burnout-out kinetics are in line with experimental findings.