Generation of fast propagating combustion and shock waves with copper oxide/aluminum nanothermite composites

Abstract

Nanothermite composites containing metallic fuel and inorganic oxidizer are gaining importance due to their outstanding combustion characteristics. In this paper, the combustion behaviors of copper oxide/aluminum nanothermites are discussed. CuO nanorods were synthesized using the surfactant-templating method, then mixed or self-assembled with Al nanoparticles. This nanoscale mixing resulted in a large interfacial contact area between fuel and oxidizer. As a result, the reaction of the low density nanothermite composite leads to a fast propagating combustion, generating shock waves with Mach numbers up to 3. © 2007 American Institute of Physics. ͓DOI: 10.1063/1.2787972͔ Nanothermite materials are comprised of a physical mixture of inorganic fuel and oxidizer nanoparticles. Nonhomogenous distribution of fuel and oxidizer has been observed in the microstructures. 1 This produces random hot spot density distribution and decreases the propagation speed of the combustion wave front. It is, therefore, important to achieve homogenous mixing of the oxidizer and fuel components for faster reaction kinetics. This can be achieved by selfassembly of fuel around the solid oxidizer. Enhancement in the combustion wave speed has already been reported for composites containing porous oxidizers and fuel nanoparticles, 2,3 and also for electrostatically charged selfassembled composites. 4 Recently, we reported that higher combustion wave speeds were achieved for the composites of ordered porous Fe 2 O 3 oxidizer and Al nanoparticles 5 as compared with the one containing porous oxidizer with no ordering of the pores and Al nanoparticles. We have also reported the composite of CuO nanorods and Al nanoparticles exhibiting a combustion wave speed of 1500Ϯ 100 m / s, which enhances to 2200 m / s for the self-assembled composites. 6-8 Interestingly, these higher combustion wave speeds are comparable to the lower end values of the detonation velocities ͑e.g., 2000 m / s for hydrocarbon/alkylene-air mixtures, 9 1500-2700 m / s for metallic azides and fulminates, 10 and about 3000 m / s for ammonium nitrate fuel oil͒ for explosives. 11 In conventional explosives, the gases produced during the chemical reaction develop turbulence due to a combined effect of high pressure and rapid shearing of molecular layers generating a shock wave. In a process called deflagration-todetonation transition ͑DDT͒, the wave propagates in the reactive medium creating localized high pressure at the hot spots and, after a certain run-up distance, rapid deflagration can transition to full detonation. 9 This distance depends on the dimensions of the shock tube and also the level of confinement. 9 In the case of low density superthermites, as the adiabatic reaction temperatures are several thousand degrees, the reaction products can volatilize rapidly 12 resulting in an increased level of turbulence and high localized pressures. Because of the low density and multiphase nature of reaction materials, the corresponding Chapman-Jouguet ͑CJ͒ pressure can be much lower ...

Combustion synthesis in nanostructured reactive systems

“…This approach involves the 104 organization of the plane front of the combustion wave propagat- 105 ing in one direction; recording the linear velocity of reaction front 106 propagation; the study of the thermal structure of the wave; the 107 identification of controlling stages and burning patterns. The nov- 108 elty was already in the fact that the metallothermy was not studied 109 as a process of metallurgy, but as a combustion process. Such 110 approach led further to the discovery of other (non-thermite) type 111 of combustible systems, which can be used for synthesis of 112 materials.…”

“…This 1167 characteristic makes composites a promising candidate for fast-im-1168 pulse microthruster applications [108]. It was found that 1169 nanothermite composites are capable of producing shock waves 1170 with Mach numbers up to 2.44 in an air-filled tube [109]. In general, 1171 micro-and nano-electromechanical systems and sensors are extre-1172 mely promising fields for nanothermites [110].…”

Controlling Material Reactivity Using Architecture

“…Rather, they undergo a rapid defl agration driven by an oxidation-reduction reaction (i.e., M 1 + M 2 O → M 2 + M 1 O + Δ E ). The linear fl ame propagation velocity is a commonly used metric to describe their reactivity and, to date, most research efforts have focused on enhancing kinetics by decreasing the mixing scale between constituents through mechanical milling, [ 11 ] core-shell [ 12 ] or laminate structures, [ 13,14 ] self-assembly, [ 15 ] or by replacing micrometer particles with nano particles. [ 16 ] While these methods have been shown to improve reactivity, further advances will likely be limited by processing constraints such as particle size, degree of mixing, passivation, sensitivity, and cost.…”

Micropatterning of nanoenergetic films of Bi2O3/Al for pyrotechnics

“…4 Packed or patterned nanoenergetic materials are suitably utilized in various applications such as safe arm and re devices, 3 microthrusters 5 molecular gene delivery 6 as well as pyrotechnic microinitiators.…”