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M6.8.1

Characterization of Metallic and Metal Oxide Nanoparticles Produced by Electrothermal-Chemical Synthesis Kurt A. Schroder, Dennis E. Wilson, Kyoungjin Kim, and Henry E. Elliott Jr. Nanotechnologies Inc. 1908 Kramer Lane, Building B, Austin, TX 78758, U.S.A.

ABSTRACT Electrothermal-Chemical Synthesis (ETCS) is a relatively new process for the synthesis of nanocrystalline powders. With ETCS nanoparticles are formed through the controlled chemical reaction of a metal plasma, produced by cathode erosion, with a gas. By controlling the quench rate of the plasma precisely, the average particle size can be varied from as small as 6-8 nm up to 100 nm and above. The process is quite versatile and can be used to produce a wide variety of nanopowders including metals, oxides, and nitrides. However, before the nanoparticles produced by this process (or any other process for that matter) can find wide scale commercial acceptance, their physical properties must be characterized. Among many characterization techniques, electron microscopy can provide structural, chemical, and morphological information on nanoparticles. In this paper, we will discuss the SEM and TEM characterization of metal and metal oxide nanoparticles powders produced by ETCS. INTRODUCTION Nanocrystalline materials are attractive due to their unique properties compared with larger-sized materials. The increased surface area to volume ratio of nanosized materials can significantly change thermodynamic and transport properties, e.g., depression of the melting point, higher sintering rate at lower temperature, and increased energetic content.1-4 Improved mechanical properties, such as increased hardness and strength, improved ductility, and good thermal shock resistance, can also be obtained.4-7 Nanomaterials have been synthesized by various methods including ball-milling, ion beam evaporation, laser ablation, sol-gel method, and chemical precipitation.8 However, each of these processes has limitations in terms of the kinds of powders and powder properties they are capable of producing. These limitations include compositional purity, surface functionalization, particle size, particle size distribution, and agglomeration. Recent work has demonstrated that plasma synthesis of nanoparticles by electrothermalchemical (ETC) synthesis can overcome these limitations. ETC synthesis relies upon a unique device powered by high-magnitude current pulse to produce various kinds of pulsed plasma vapors. This device was originally developed to utilize high pressure and high velocity plasma jets to increase the acceleration of launchable projectiles beyond that which would be possible with conventional propellant igniters.9 Recently, a new type of hybrid electrothermal-chemical (HETC) device was designed and tested to produce various nanophase ceramic and metallic particles by the reaction of the discharged metal plasma jet with a background quenching gas.10,11 Those works demonstrated that plasma synthesis by the HETC device could be a promising candidate for energy-effi