Mechanochemical Ignition of Self-propagating Reactions in Zn-S Powder Mixtures

The present work examines the mechanochemical reactivity of Zn-S powder mixtures subjected to mechanical processing by ball milling. Chemical composition, collision energy, powder charge inside the reactor, number of milling balls, Zn microstructure and temperature have been systematically varied to gain detailed information on the physical and chemical responses of reactant powders. It is shown that the mechanical activation of mixtures with intermediate Zn contents determines the ignition of self-sustaining high-temperature reactions that lead to the α and β ZnS line compounds and residual unreacted elements. Within the intermediate compositional range, ignition time decreases as the impact energy, the number of milling balls and the temperature increase and as the mass of powder decreases. In contrast, ignition times decrease as the hardness of Zn powder increases. Experimental findings are interpreted with the help of a phenomenological kinetic model.