A combustion synthesis process for synthesizing nanocrystalline zirconia powders
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Materials with nanocrystalline features are expected to have improved or unique properties when compared to those of conventional materials. Methods for the practical and economical production of nanoparticles in large quantities are not presently available. A method based on combustion synthesis for preparing nanocrystalline powders was investigated in this work. Yttria-doped zirconia powders with an average crystallite size of 10 nm were synthesized. The characteristics of the powder (e.g., surface area and phase content) were found to depend strongly on the fuel content in the starting mixture and on the ignition temperature used in the process. The method is expected to be suitable for commercial fabrication of nanocrystalline multicomponent oxide ceramic powders.
I. INTRODUCTION
Nanocrystalline materials have received considerable attention during the last few years, since they are expected to have improved or unique properties as compared to those of conventional materials.1"3 Because the grain size in these materials is on the order of 1 to 100 nm, a relatively large fraction of the atoms in the nanocrystallite reside at the grain boundaries or interfaces in the material. The combination of a relatively large fraction of interfacial atoms and the large fraction of grain boundary atoms (and thus interfacial area) per unit volume, along with the interaction of photons, electrons, or dislocations with the material's nanoscale features, can lead to unusual mechanical, optical, electronic, and magnetic properties. Dense nanocrystalline materials are generally fabricated from nanocrystalline powders. The various methods that are available for producing small quantities of nanoparticles have been summarized by Gleiter.1 Synthesis of nanoparticles involves either (i) assembling ultrafine particles from their constituent atoms or molecules, or (ii) reducing relatively larger particles to their ultimate, fine, final particle size. Sputtering, laser ablation, gas-phase condensation, sol-gel processing, etc., belong to the first group, while high energy milling and mixalloy processes belong to the second. The above methods are, of course, simply laboratory-scale processes, producing small quantities of the product material. The most plausible, practical reason for this extremely low production rate is that the dispersions of nanoparticles in each of these processes must be highly dilute in order to limit the size of both primary particles and particle clusters. Fewer of these methods have been applied to the synthesis of multicomponent (e.g., bi748
http://journals.cambridge.org
J. Mater. Res., Vol. 10, No. 3, Mar 1995
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nary or ternary metal oxide) compounds. High-reliability methods for the inexpensive production of large quantities of high-quality, multicomponent nanoparticles are thus needed for commercial applications to be realized. A method for preparing nanocrystalline powders that is based on a combustion synthesis process is reported in this paper. The method relies on the principles
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