COLL 393 |
| Michael R. Zachariah1, Kihong Park1, and Donggeun Lee2. (1) Department of Chemistry, University of Maryland and NIST, College Park, MD 20754, (2) School of Mechanical Engineering, Pusan National University, Busan 609-735, South Korea |
| Aluminum nanoparticles are being considered as a possible fuel in advanced energetic materials application. Of considerable interest therefore is a knowledge of just how reactive these materials are, and what the effect of size on reactivity is. In this paper we describe results of size resolved oxidation rate using a recently developed single particle mass spectrometer (SPMS). Aluminum nanoparticles used were either generated in-house by DC arc discharge or laser ablation methods, or by use of commercial aluminum nanopowders. These particles were oxidized in a flow reactor in air for specified residence time (25 oC ~ 1100 oC) and subsequently sampled by the SPMS. The mass spectra obtained were used to quantitatively determine the elemental composition of individual particles and their size. We found that the reactivity of aluminum nanoparticles is enhanced with decreasing primary particle size. Aluminum nanoparticles produced from the DC arc, which provided primary particle size of the smallest size (~15 nm), were found to be the most reactive (~99% aluminum nanoparticles oxidized to aluminum oxide at 900 oC). In contrast, nanopowder with primary particle size greater than ~80 nm was not fully oxidized even at 1100 oC. We also determine the size-dependent reaction rate constants and Arrehenius parameters (activation energy and pre-exponential factor). We found that as particle size decreases, the reaction rate constant increases and the activation energy decreases. For example, the activation energy for oxidation of DC arc-generated aluminum nanoparticles was only 24 kJ/mol for particles smaller than 50 nm, but increased to 94 kJ/mol for particles in the size range from 100 to 150 nm. |
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Nanoscience and Nanotechnology
8:30 AM-11:45 AM, Wednesday, March 31, 2004 Marriott -- Orange County 5, Oral
Division of Colloid and Surface Chemistry |