Engineering aerosol-through-plasma torch ceramic particulate structures: Influence of precursor composition
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Claudia Luhrs and Chunyun Peng University of New Mexico, Mechanical Engineering, Albuquerque, New Mexico 87131
Paul Fanson Toyota Motor Engineering & Manufacturing North America, Inc., Catalyst Materials, Ann Arbor, Michigan 48105
Hugo Zea University of New Mexico, Mechanical Engineering, Albuquerque, New Mexico 87131 (Received 19 June 2007; accepted 5 February 2008)
This is the second in a series of articles demonstrating the unique character of the aerosol-through-plasma (A-T-P) process for producing nanoparticles. This study is focused on the impact of two parameters, cation ratio (1:3, 1:1, 3:1) and solvent (evaporated prior to generation of aerosol), on the structures of Ce:Al oxides particles. These two simple changes were found to impact virtually every aspect of particle structure, including the fraction of hollow versus solid, fraction of nanoparticles, phase structure, and even the existence of surface phase segregation. CeAl mixed oxides were found only over a limited range of compositions, and that range was a function of the solvent. At all other cation ratios, only ceria was a crystalline phase, and most if not all the alumina is amorphous. It is notable that the fraction of hollow micron-sized particles and nanoparticles is greatly influenced by the cation ratio and solvent identity. Indeed, significant numbers of nanoparticles were only produced using an aqueous precursor with a Ce:Al ratio of 1:1. Another unique finding is that phase segregation exists in individual particles on the length scale of nanometers. This study compliments an earlier study of the influence of operating conditions on particle structure. Taken together, the studies suggest a means to engineer (as well as limits to the engineering possibilities) ceramic particle structures using the A-T-P method.
I. INTRODUCTION
Recently, we showed that relatively high surface area (>25 m2/gm) multicationic nanoparticles can be generated by passing either “dry” or “wet” aerosols containing dissolved precursor salts through a microwave plasma torch operated at atmospheric pressure.1 This was the most recent in a series of studies designed to demonstrate that the aerosol-through-plasma (A-T-P) technique can be readily modified to produce a wide range of material classes. Earlier efforts produced spherical micron-scale BN2,3 (a truly novel material), nanometal particles,4,5 spherical ceramics6,7 supported metal catalysts,8,9 and even carbon nanotubes.10 The earliest study11 established that metal and metal oxide nanoparticles could be gena)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2008.0233 1870
http://journals.cambridge.org
J. Mater. Res., Vol. 23, No. 7, Jul 2008 Downloaded: 14 Mar 2015
erated using the A-T-P method, and work on metal, metal oxide, nitrides, and other types of nanoparticles using variations on the method continues.12,13 One novel feature of the multication oxide ceramics (Ce–Al–O) described in the most recent study1 was the existence of bimodal particle distributions; tha
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