Understanding and Tuning the Reactivity of Nano-Energetic Materials
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Understanding and Tuning the Reactivity of Nano-Energetic Materials A. Rai, L. Zhou, A. Prakash, A. McCormick, M. R. Zachariah* Department of Mechanical Engineering and Department of Chemistry, University of Maryland, College Park, USA *Corresponding Author: [email protected]
ABSTRACT Mixtures of fuel and oxidizers with particle sizes in the nanometer range have been widely used for energy intensive applications like propellants and explosives. Nano- Al is invariably used as fuel, while a host of metal oxide nanoparticles are used as oxidizers. This article aims at understanding and tuning the reactivity of these nano-energetic materials. The first part of this article discusses the oxidative reactivity of aluminum nanoparticles as measured experimentally using single-particle mass-spectrometer (SPMS) and microscopy and then modeled. Experimental evidence suggests that outward diffusion of aluminum is an important phenomenon in the oxidation of aluminum nanoparticle. Also melting of the aluminum core is necessary for the reaction to take place vigorously. In the second part of the paper we discuss the formation of novel oxidizers. A super-reactive formulation of Al/KMnO4 has been developed which is shown to be orders of magnitude more reactive than the traditional formulations of Al/ Fe2O3, Al/MoO3 and Al/CuO. We demonstrate the formation of novel composite oxidizers to tune the reactivity of the Al/Metal oxide system.
INTRODUCTION The emphasis of the energetic materials research lies on the development and characterization of propellants, explosives and pyrotechnics for civil and military applications. Reactivity of inorganic metallic fuels has been an extensive area of research, because of their high energy density. Typical preparation of inorganic energetic materials involves physical mixing of solid fuel which is a metal and oxidizer which is usually a metal oxide. Most commonly used thermite reactions for explosive applications are Al reacted with other metal oxides usually, Fe2O3, MoO3 and CuO. Mixtures of oxidizer and fuel with particle sizes in the nanometer range have been widely used for energetic material applications and are termed Metastable Intermolecular Composites (MIC). The prevailing wisdom in the potential use of nano-scale energetic materials is a presumed reduction in mass transport limitations due to reduced particle size and increased surface area. The primary focus of this article is to understand and tune the reactivity of these nano-energetic materials. The first part of this articles deals with understanding the reactivity of aluminum and the second part deals with the formation of metal oxide particles and tuning the reactivity using novel approaches. Aluminum nanoparticles have gained importance in the recent years because of their potential application as an energetic material. Ivanov et al.1 reported that by adding aluminum nanoparticles in a propellant formulation, the burning rate could be enhanced by the factor of 510. Aumann et al.2 showed that the activation energy for
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