Role of infiltration in spin combustion in gas-solid systems

In the present work, based on experimental investigations of reaction propa gation in Ta-N and Ti-N systems, we show that infiltration plays a key role in the mechanism of spin mode combustion. The influence of two main parame ters of infiltration combustion, initial sample density (rho) and reactant gas pressure (P), was investigated. Based on the results, pressure-density (P-rho) diagrams are constructed, which present the regions of different wa ve propagation behavior. For example, it is shown that for both systems a r ange of nitrogen pressure exists where by increasing initial sample density one passes from spin to steady planar mode, with decrease of combustion ve locity. Also, for a range of rho, decrease of P leads to combustion limit w ithout observation of spin or oscillation modes. Further. it is shown that the phase composition of products depends on the combustion mode. A variety of questions arise from this work. While qualitative explanations are prov ided in this paper, we believe that quantitative answers to these and other questions may be obtained only from models that account for infiltration a nd the heterogeneous nature of the process. (C) 2000 by The Combustion Inst itute.