DEPENDENCE OF COMBUSTION VELOCITY ON THE MEDIUM MICROSTRUCTURE

Abstract

Self-propagating high-temperature synthesis (SHS) isaprospectivetechnology for production of variouspowders, material sanditems, which has growingin dustrial applications. Asignificant contribution inthisfieldismade by the Institute of Combustion Problems, its Founder Director G.I. Ksandopulou and General Director Z.A. Mansurov. A linear velocity of the combustion propagation is one of the most important characteristics of the process. I tinfluences productivity of the synthesis; well-controllab levalues of velocity have a great significance for creatinguniform conditions in materials synthesis, as well as for future pyrotechnical applications. The classical combustion the oryestablis hes directcor respondence of the propagation velocity with reaction heat release rate. For the heterogeneous SHS systems, it is of ten assumedthatthereactionrateis inversely proportional to the sizes of reactant particles. However, experimental results obtainedbyvarious researchers, differ several time seven for the same particle sizes. Thisindicatesexistence of hidden parameters thatarenotconsideredintraditional quasi-homogeneous models. In this work, wereportnew experimental resultson the combustion regularities of SHS-compositions depending on particle size and mechanical activation. The seresultsshow that combustion velocitymayincrease with in creasing particle size, and this effect was observed for gasless and for hybrid (solid-gas) systems. Combustion of mono-dispersed powder mixture soccurs with highervelocityascompared with poly-dispersed compositions. Thus, heat transferbet ween particles, rather than chemical reaction rate, is alimitingstage of the combustion propagation process. Itis shownthat combination of short-term mechanical activation with cold rolling allows 50% increasing of the combustion velocity of Ti-B SHS mixture. The obtained results canbe applied for development of new gasless energetic compositions with pre-determined combustion velocity, and for optimization of materials synthesis regimes.