Dynamics of self-propagating reactions in heterogeneous media: experimentsand model

The extreme reaction conditions during combustion synthesis (CS) process re quire new methods for controlling the microstructure (and hence, the proper ties) of the desired materials. It appears that the structural changes whic h determine the microstructure and phases are influenced by local variation s in reactant composition and temperature. A direct observation of the micr ostructural transformations during CS was made using a novel digital high-s peed microscopic video recording technique, with imaging rates up to 12,000 frames/s and magnification up to 800 x. It was shown that over a wide rang e of experimental conditions, macroscopically steady reaction fronts in het erogeneous mixtures exhibit random microscopic fluctuations in shape and in stantaneous velocity, which are directly related to the microstructure of t he reaction mixture. These fluctuations were correlated with the initial he terogeneity of the reaction medium. In conjunction with these experiments, a micro-heterogeneous cell model was developed to describe the local reacti on wave propagation in a heterogeneous porous medium. The calculated combus tion front profiles compared well with the experimental results. (C) 2001 E lsevier Science Ltd. All rights reserved.