Nano-sized amorphous alumina particles obtained by ball milling ZnO and Al powder mixture

Abstract

Solid state reduction reaction of ZnO and Al powder mixtures induced by mechanical alloying has been investigated. It is revealed that the reduction product consists of crystalline zinc and amorphous alumina particles with nanometer sizes of 10–50 nm. The zincite is found to be reduced by Al through a diffusion-controlled mechanism, rather than a rapid self-sustaining combustion reaction process. This is attributed to the fact that the calculated theoretical adiabatic temperature for the reaction is far below the critical one to trigger the mechanical alloying induced combustion when evaporation of zinc is taken into consideration. The amorphous structure of the produced alumina, which consumes excess enthalpy released during the reaction, further lowered the theoretical adiabatic temperature. The gradually proceeding redox reaction sustains a relatively low temperature environment, which favors the formation of the amorphous alumina.