Solid-state combustion in mechanically activated SHS systems. I. Effect of activation time on process parameters and combustion product composition

The factors responsible for the transition from reagent interaction involving a liquid phase in ordinary SHS powder mixtures to solid-state combustion after preliminary activation of these mixtures in an energy-intensive planetary mill were studied for Ni + 13 wt.% Al and Ni + 45wt.% Ti compositions. The dependences of the burning rate and temperature on the duration and conditions of mechanical activation were determined. It is found that the occurrence of solid-state SHS in a powdermixture is due to the formation of “laminated composites”, in which the reagents are ground to ultrafine size, the area of their contact increases severalfold, and the concentration of nonequilibrium defects is high. In activated samples, heat release proceeds in several stages and at lower temperature than in powder mixtures.