CHANGE IN POROSITY DURING COMBUSTION OF HETEROGENEOUS SYSTEMS WITH PARTLY GAS-PHASE PRODUCTS

On the basis of a representation of the mechanics of heterogeneous media, a model of self-propagating high-temperature synthesis is constructed. This model accounts for macrostructural transformations which are related to the difference in densities of the initial materials and their products. Liquid-phase sintering and the decompacting action of gas percolating through pores are also taken into account. Formulas for the burn rate and the final porosity are obtained by using approximation methods. The influence of the governing parameters is studied: particle dimensions, initial porosity, sample diameter, presence of volatile impurities, etc. The critical conditions are found for disruption of the continuity of the medium, for which break-up of the specimen takes place.