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Self-propagating formation reactions have been studied in multilayer foils and they are currently being investigated for applications in joining and ignition. Here, we introduce a reactive multilayer foil which contains a reduction-oxidation thermite reaction between CuOx and Al. Typically in reactive multilayer foils, elemental layers react and form a single intermetallic product. In this thermite reaction, however, aluminum and copper oxide are, respectively, oxidized and reduced and form aluminum oxide and copper. The fully dense multilayer foils provide a well-defined geometry for studying the thermodynamics, kinetics, and intermediate phase formation in the CuOx/Al thermite reaction. Here, sputter deposition of CuOx/Al multilayer foils is demonstrated, and x-ray diffraction and transmission electron microscopy, including high resolution transmission electron microscopy and electron spectroscopic imaging, are used to characterize the as-deposited foil and the final products. The heat released in the reaction is quantified using differential thermal analysis, and the velocity of the self-propagating reaction is reported.

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.

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While processing techniques for deposition of CuOx/Al multilayer foils were being developed, a method for synthesizing paramelaconite (Cu4O3) was serendipitously discovered. These paramelaconite films were successfully synthesized by sputter-deposition from a CuO target. Milligram quantities of uncontaminated material were produced enabling new studies of the morphology, stoichiometry, and thermodynamics of this unique copper oxide. At moderate temperatures, equiaxed paramelaconite grains deposited with a strong out-of-plane texture; at lower temperatures the paramelaconite grains showed no texture but were columnar in geometry. X-ray photoelectron spectroscopy showed that the as-deposited Cu4O3 had a nonstoichiometric Cu:O ratio of 1.7:1; the ratio of Cu+ to Cu2+ was 1.8:1. On heating, this phase decomposed into CuO and Cu2O at temperatures ranging from 400 to 530 °C. Using differential scanning calorimetry, the heat of formation and Gibbs free energy for Cu4O3 were estimated to be −453 and −279 kJ/mol, respectively. On the basis of these calculations and our observations, we confirmed that Cu4O3 is a metastable phase.