Reductive/expansion synthesis of zero valent submicron and nanometal particles
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Claudia C. Luhrs University of New Mexico, Department of Mechanical Engineering, Albuquerque, New Mexico 87131
Jonathan Phillipsa) University of New Mexico, Department of Mechanical Engineering, Albuquerque, New Mexico 87131; and Los Alamos National Laboratory, Los Alamos, New Mexico 87544 (Received 2 August 2010; accepted 12 October 2010)
Upon rapid heating to a high temperature (~800 °C), mixtures of nitrate compounds and urea created nano and submicron metal particles. The process (reductive/expansion synthesis, RES) results in atomic scale mixing. The product formed from mixed-nitrate (Fe + Ni) salts and urea created true metallic alloy. Unlike other product-from-powder synthesis processes, this process produced only zero valent metal. Initial work suggests this method is a scalable and efficient means for making metallic nanoparticles. Although this is primarily a phenomenological report, a preliminary model is presented: Initially, nitrates decompose to oxide; thus in the absence of urea metal oxide particles form, as in the case of combustion synthesis. In the case of urea/nitrate mixtures, there is a “convolution” of decomposition processes. Urea decomposes to yield reducing gases, leading to the formation of metal rather than oxide. Rapid “expansion” of gas leads to “shattering,” resulting in highly dispersed particles.
I. INTRODUCTION
Many applications have been proposed for nanoparticles: armor, surface coating, data storage, inks, bioimaging applications,1–3 sinter-resistant plasma-generated catalysts.4–7 The recent demonstration that complex nanoparticles, that is nanoparticles with multiple shells,8,9 and/or designed void spaces,10 suggests other applications such as anode or cathode materials for high-energy density batteries, and light, high energy density solid fuels. Enabling these technologies will require means to make large quantities of nanoparticles. There are many processes for making primarily metallic nanoparticles including several aerosol techniques: aerosol-through-plasma (A-T-P),4–13 evaporation of solvents from small drops containing dissolved salts14,15 and flame synthesis.16–18 Nonaerosol processes for making nanometal particles include metal gas evaporation,19 metal evaporation in a flowing gas stream,20 mechanical attrition,21 sputtering,22 electron beam evaporation,23 electron beam induced atomization of binary metal azides,24 expansion of metal vapor in a supersonic free jet,25 inverse micelle techniques,26 laser ablation,27 laserinduced breakdown of organometallic compounds,28 and pyrolysis of organometallic compounds.29 a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2010.66 672
J. Mater. Res., Vol. 26, No. 5, Mar 14, 2011
http://journals.cambridge.org
Downloaded: 30 Jan 2015
The present technique, reductive/expansion synthesis (RES), is not closely related to any of the aforementioned in terms of either process or mechanism. The process, clearly unique, requires only two steps: (i) molecular, partially oxidized metal precursors (e.
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