Research on combustion characteristics of nano-Al/CuO thermite composites

Abstract

Thermites are solid composites of metal and metal oxide which have large combustion enthalpy. From this property, they have been focused in military and industrial applications. Especially, composites of aluminum (Al) and copper oxide (CuO) are representative materials and have much higher combustion enthalpy than that of commercial explosive materials like TNT. However, it is observed that long delay for ignition and slow rate of energy release in micro-sized thermite. By introducing nano-sized Al and CuO, much vigorous combustion performance was achieved due to increased surface area and decreased activation energy for oxygen release from CuO. In this study, we investigated combustion characteristics of nano-Al/CuO composites for designing efficient thermite composites. We studied off-stoichiometry phenomenon which is generally observed in various thermite materials. While theoretical ratio for the thermite reaction of Al and CuO is 2:3, our experiment results showed that the maximum pressurization rate is observed when more Al is provided, Through XRD and TEM analysis, it is found that unreacted Al NPs are capped with Cu layer after reaction. We attribute the deposition of Cu layer on the surface of Al NPs to the off-stoichiometry because some Al NPs are deactivated due to passivation of Cu layer. Based on our experimental data and conceptual interpretation, we proposed ignition mechanism Al/CuO composites. We also studied the combustion behavior of Al nanoparticles (NPs) and CuO nanowires (NWs) com-posites. CuO NWs were synthesized by oriented attachment of $Cu(OH)_2$ NPs and dehydration process with calcination at $120^\circ C$. From electron microscopy images, it is found that synthesized CuO NWs have similar diameter regardless of the aging time. An X-ray diffraction analysis revealed that aspect ratio of CuO NWs are increased with extending aging time, while their domain size is nearly identical. It is shown that the max-imum pressurization rate of Al NPs/CuO NWs occurs when CuO NWs have a certain aspect ratio. This indi-cates that both the degree of mixing between Al and CuO and surface area of CuO NWs are relevant factors.