Reactivity of mechanically activated powder blends: Role of micro and nano structures

Abstract

Experimental study of reactive powder blends (largely Ni + Al mixures) was made in order to reveal a role of micro to nano structural transformations during mechanical activation in improving the reactivity of activated blends. The blends were processes in planetary ball mills, and the temperature (T ig) of reaction initiation (self-ignition) was measured. Microstructure of activated compositions was characterized by SEM and TEM. T ig was found to strongly depend on the intensity and duration of mechanoactivation. Microstructural analysis has shown that nanosized sites of highly reactive precursors are formed during the activation process, apparently as a result of dry friction of the reactants. An increase in the amount of these sites causes a gradual decrease in T ig for activated blends.