Chemical Processing of Nanostructured Materials
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Chemical Processing of Nanostructured Materials 1∗
R. N. Das
Department of Metallurgical Engineering and Materials Science Indian Institute of Technology, Bombay, Powai, Mumbai-400076, India 1
Present address: School of Mechanical and Materials Engineering, Washington State University, Pullman, WA 99164-2920, USA ∗ Member Materials Research Society ABSTRACT Nanocrystalline ( particle diameter less than 50 nm) ceramic powders have been prepared by the rapid evaporation of precursor solutions containing the respective metal nitrates/ hydroxides, triethanolamine (TEA) and sucrose in stoichiometric amounts. Complete evaporation of the solutions yields a fluffy dried precursor mass. Heat-treatment of the precursor mass at low external temperatures (450-700 0C) resulted in the desired nanocrystalline oxides. The oxide system studied are: barium titanate (BaTiO3), lanthanum modified lead zirconate-titanate (PLZT), Nickel ferrite (NiFe2O4) and Calcium Tungstate (CaWO4). INTRODUCTION Recent years have seen a surge of interest in synthesis and processing of nanocrystalline ceramic powders. Often these advanced ceramic materials are tailor made to suit specific applications, and the chemical synthesis routes play a crucial role in their design and production. The use of chemistry in the preparation of materials can avoid three major problems - diffusion, impurities and agglomeration. The reasons being that the fine chemically prepared powders allow for shorter diffusion distances and improved homogeneity, the chemical precursors used can be easily refined to increase the purity, and careful control of solvent removal from the precursors will lead to the production of crushable agglomerates. Over the last few decades, a number of chemical synthesis techniques have been developed for the preparation of nanocrystalline powders. Most often, the technique begins with the preparation of a precursor solution, in which the ions are well-mixed on a molecular scale. These techniques then employ a variety of methods (such as : spray drying, freeze drying, solgel, and coprecipitation) for obtaining the first solid phase from the precursor solution. These solid phases are physical mixtures of crystalline solid intermediate phases (such as oxides, hydroxides, carbonates, oxalates or, cyanides) which are heated to cause decomposition and reaction to the desired multi-component oxide phase [1-5]. Another group of synthesis techniques seeks to form an amorphous solid intermediate from the liquid precursor. For example, the Pechini [6] or, amorphous citrate [7-10] processes which form intermediate amorphous solids that are subsequently decomposed and thermally reacted to form complex oxide phases. Recently, several variant of self-sustaining combustion synthesis [11- 13] have been developed. Unlike the Pechini or amorphous citrate processes, these self-sustaining combustion processes are rapid and may approach direct conversion from the molecular mixture of the Y3.10.1
precursor solution to the final oxide product, avoiding formation of in
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