Home – Home – Jornals – Chemistry for Sustainable Development 2005 number 2

The mechanisms of synthesis processes and mechanochemical reactions in the dynamically loaded layer of a powder mixture able to undergo gas-free self-propagating high-temperature synthesis (SHS) are investigated by means of computer simulation. Within the model of reacting powder medium, the related problems of shock compaction, establishment of thermal balance, filtration of a melt of the low-melting component, and macrokinetics of chemical transformations are considered. We take into account the macroscopic structure of concentration non-uniformity of the initial powder mixture, the possibility of mechanical activation of the reacting components during shock compression, and modification of the parameters of state and structure at all the stages of synthesis. The plastic deformation of crystal structure and destruction of the surface layers of powder particles are considered to be the decisive factors of mechanical activation. The model of reaction cell of Arrhenius type with variable macrokinetic parameters is used. The activation energy of the reacting mixture is considered to be a linear function of the work of plastic deformation and the work of destruction of the surface layers of particles. The pre-exponential factor agrees with the power-behaved reaction diffusion. The powder body is represented by a model system of powder components with the given structural parameters, physical and chemical characteristics; the structure of the powder layer is represented by the model regular structure of the cells of concentration non-uniformity. Powder mixtures of Ti-Al and Ti-C types preliminarily pressed to the required mean porosity are considered in the computational experiment. The factors determining changes in the reactivity of the reacting powder mixture during mechanical load are considered, as well the effect of the formation of a structure with nanometer-scale morphological elements are investigated.