Oxidation Dynamics of Aluminum Nanorods

  • PDF / 4,644,020 Bytes
  • 6 Pages / 612 x 792 pts (letter) Page_size
  • 55 Downloads / 231 Views

DOWNLOAD

REPORT


Oxidation Dynamics of Aluminum Nanorods Ying Li, Aiichiro Nakano, Rajiv K. Kalia, and Priya Vashishta Collaboratory for Advanced Computation and Simulations Departments of Chemical Engineering and Materials Science, Physics and Astronomy, and Computer Science University of Southern California, Los Angeles, CA 90089-0242, U.S.A. ABSTRACT Understanding of combustion of metastable intermolecular composites, including the burning of aluminum nanoparticles, is critical for broad applications such as propulsion, explosives and other pyrotechnics. Aluminum nanorods (Al-NR) with oxidized shells are good candidates for stable fuel-oxidizer combinations. We investigate the oxidation dynamics of AlNRs of different diameters (26, 36 and 46 nm) but the same aspect ratio using molecular dynamics simulations. We heat one end of the Al-NR to 1100 K and then study the oxidation reaction at the interface of the alumina shell and the Al core. We find: (1) heat produced by oxidation causes the melting of nanorods; (2) heat release is accelerated due to Al-O reaction at outside-shell and core-shell interfaces; and (3) the larger surface-to-volume ratio causes faster burning of thinner nanorods. We present results for the oxidation speed of nanorods. INTRODUCTION Aluminum powder has been used as propellants for many years because of the high energy release rate [1], low ignition temperature [2], and rapid heat propagation [3]. It is well known that during the combustion of aluminum powder propellant, particles could initially melt and coalesce into large agglomerates [4, 5]. There are various possible mechanisms of adhesion between the initial aluminum particles and the agglomerates [6, 7]. The slow burning and heterogeneity of these agglomerates may be detrimental to the performance of continuous combustion (e.g. due to incomplete aluminum combustion, instabilities, and slag formation, etc.) [8-10]. There is a critical need for a new morphology of aluminum powders to solve these issues. Several experiments were attempted to enhance the inhomogeneous distribution of oxidizer and fuel [11, 12]. For example, cylindrical nanoparticles [13] and mesoporous structure of oxidizer [14] were tested. These alternative structures were selected over the spherical oxidizers because of the higher surface area available for the arrangement of fuel nanoparticles around them. However, no experiment has been conducted on altering the structure of the fuel nanocomposites, especially the combustion of aluminum nanorods. Advancement of synthetic techniques has enabled the production of aluminum nanorods, including thermolytic methods, vapor deposition, metal-exchange chemistry, electromigration, and colloidal lithography [15-19]. Combustion of aluminum nanorods is expected to be efficient because of their relatively high surface-to-volume ratios. A major question is how morphological design of aluminum nanorods affects the combustion performance. We address this issue from the atomistic level using molecular dynamics (MD) simulations.

SIMULATION PROCEDURE

Data Loading...