Solid state displacement reaction of Fe and CuO induced by mechanical alloying

Abstract

We report on studies of solid state redox reactions induced by mechanical alloying (MA). The displacement reaction in the FeCuO system during MA may be completed by two steps: a rapid self-sustaining combustion reaction process, followed by a gradual reaction process. High densities of point and lattice defects, as well as a fine dispersion of reactants, are introduced in the powder mixture during MA. In addition, the displacement reaction in the FeCuO system produces a large negative heat. This combination of factors makes the redox reaction occur in the reaction regions, accompanied by self-heating. The self-heating may raise the temperature up to ignition temperature for a combustion reaction; this ignition temperature is greatly decreased by ball-milling. Combustion then takes place. The displacement reaction may be carried out rapidly during combustion. Complete reduction of copper oxides, including the intermediate oxidation state phase, Cu 2O, appearing immediately after combustion, is observed after prolonged milling, during which the reduction is gradual; a similar self-sustaining reaction mechanism works in local reaction regions.