Investigating the reaction path and growth kinetics in CuOx/Al multilayer foils

CuO x / Al exothermic reactions in multilayer foils were studied to identify reaction paths and reaction kinetics. Heating samples at a slow, controlled rate in a differential thermal analyzer showed that the reduction of CuOx and the oxidation of Al proceeded via two separate exotherms. To analyze this reaction pathway, samples were heated to various temperatures within these exotherms, quenched, and characterized with x-ray diffraction, Auger depth profiling, and transmission electron microscopy. Experimental evidence indicates that in the first reaction, CuOx is reduced to a mixture of CuO and Cu2O and an interfacial layer of Al2O3 grows to coalescence; the final products of the second exotherm are Cu, Al2O3, and Cu2O. The first exotherm was believed to be controlled by the two-dimensional, interface-limited growth of the Al2O3 layer, while the second exotherm was believed to be controlled by both the diffusion-limited one-dimensional growth of the Al2O3 and the interface-controlled growth of the Cu due to the reduction of Cu2O.