Interfacial Chemistry in Al/CuO Reactive Nanomaterial and Its Role in Exothermic Reaction

Abstract

Interface layers between reactive and energetic materials in nanolaminates or nanoenergetic materials are believed to play a crucial role in the properties of nanoenergetic systems. Typically, in the case of Metastable Interstitial Composite nanolaminates, the interface layer between the metal and oxide controls the onset reaction temperature, reaction kinetics, and stability at low temperature. So far, the formation of these interfacial layers is not well understood for lack of in situ characterization, leading to a poor control of important properties. We have combined in situ infrared spectroscopy and ex situ X-ray photoelectron spectroscopy, differential scanning calorimetry, and high resolution transmission electron microscopy, in conjunction with first-principles calculations to identify the stable configurations that can occur at the interface and determine the kinetic barriers for their formation. We find that (i) an interface layer formed during physical deposition of aluminum is composed of a mixture of Cu, O, and Al through Al penetration into CuO and constitutes a poor diffusion barrier (i.e., with spurious exothermic reactions at lower temperature), and in contrast, (ii) atomic layer deposition (ALD) of alumina layers using trimethylaluminum (TMA) produces a conformal coating that effectively prevents Al diffusion even for ultrathin layer thicknesses (∼0.5 nm), resulting in better stability at low temperature and reduced reactivity. Importantly, the initial reaction of TMA with CuO leads to the extraction of oxygen from CuO to form an amorphous interfacial layer that is an important component for superior protection properties of the interface and is responsible for the high system stability. Thus, while Al e-beam evaporation and ALD growth of an alumina layer on CuO both lead to CuO reduction, the mechanism for oxygen removal is different, directly affecting the resistance to Al diffusion. This work reveals that it is the nature of the monolayer interface between CuO and alumina/Al rather than the thickness of the alumina layer that controls the kinetics of Al diffusion, underscoring the importance of the chemical bonding at the interface in these energetic materials.

Reactive multilayers fabricated by vapor deposition: A critical review

“…Planar multilayers comprised of alternating metal and metal oxide layers present unique challenges [61,[76][77][78][79]. In particular, care must be taken to prevent oxidation of the deposited metal reactant layers during film growth.…”

“…As such, it is uniquely suited for the deposition of thin, conformal films onto planar and non-planar substrates, including high aspect ratio, porous structures. One application of ALD has involved the deposition of ultrathin (0.5 nm) alumina interfacial barrier layers within sputter-deposited CuO/Al (thermite) multilayers [79]. Conformal, interfacial layers effectively prevented Al reactant diffusion at room temperature and resulted in reduced multilayer reactivity [79].…”

Enhanced energy performance from core–shell structured Al@Fe2O3 nanothermite fabricated by atomic layer deposition

“…The increase in the ignition delay is dependent on the thickness of the Fe 2 O 3 shell layer, which implies that the energy release patterns of energetic nanomaterials may be tuned by applying ALD coatings on the phase interface. 53 Combustion of the Al nanopowder is quiet and slow (Fig. 9a).…”

Correlating ignition mechanisms of aluminum-based reactive materials with thermoanalytical measurements

“…In Ref. [134] focus was on modifying the interfacial Al/CuO layer by altering deposition process. Two samples were prepared: one, with CuO deposited directly onto Al, and the other, where interfacial Al 2 O 3 layers were prepared by atomic layer deposition.…”