Role of inter- and intraparticle diffusion in nonuniform particle size gasless compacted powder combustion synthesis - II: results and comparison with experiment

Following Part I, the predicted results of a combined three-scale, specimen -level/particle-level treatment of gasless, combustion synthesis of interme tallics, for a system with specimen-level composition corresponding to TiAl 3. is presented, It is shown that the intraparticle diffusion, modeled by a high reaction rate (i.e., primary-diffusion) regime followed by a lower re action rate (i,e., secondary-diffusion) regime, determines the front struct ure and the propagation speed. The nonuniform particle-size distribution li mits the availability of the reactants at a particle level, thus determinin g the extent of conversion to the final product and the maximum temperature . Experiments are performed for the aluminium-titanium system for two diffe rent titanium (higher melting temperature reactant! powder sizes. The model predicts a lower conversion than that observed in the experiments, indicat ing the importance of interparticle diffusion. There is good agreement betw een the predicted and measured variations of propagation speed and maximum temperature with respect to the average particle size. (C) 1998 Elsevier Sc ience Ltd. All rights reserved.