Nanopowder Synthesis

There are numerous ways in which ceramic powders can be synthesized solution, solid-solid or solid-gas processes. The solution processes have been increasingly used due to their peculiar characteristics. The goal of all these processes is the production of high purity powders with fine particle sizes, usually a small aggregation and/or agglomeration and produced at low costs. The process of choice, however, depends on the material in question, the application and the required amount of reagents and products. 

A method for the preparation of highly pnre and homogeneous powders, especially interesting for obtaining nanocrystalline powders snch as ceramic oxides, is solution combustion synthesis (SCS). 

Solution combustion synthesis makes use of salts, such as nitrates, metal sulfates and carbonates, as oxidants and, reducing reagents, fuels such as glycine, sucrose, urea, or other water soluble carbohydrates. Nitrate acts as an oxidizer for the fuel during the combustion reaction. The powder can be a pyrolysed product of a single phase, but usually it is a combination of metal oxides and in some cases it needs subsequent heat treatment to form single-phase products, which are usually the results required in this process. 

Material FueP Particle size Application References 

The foundation for the combustion synthesis technique lies in the thermodynamic concepts used in the field of propellants and explosives, and its extrapolation to the combustion synthesis of ceramic oxides and its thermodynamic interpretation are discussed extensively by several researchers. The success of this process is closely linked to the mix of constituents of a suitable fuel or complex-ing agent (e.g., citric acid, urea, and glycine) in water and an exothermic redox reaction between the fuel and the oxidant (e.g., nitrates). 

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Banerjee, A., Bandyopadhyay, A. and Bose, S. (2007) Hydroxyapatite nanopowders synthesis, densification and cell-materials interaction. 

Ding,)., Miao, W.F., Tsuzuki, T., McCormick, P.G. and Street, R. (1996) Mechanochemical synthesis of nanopowder. Synthesis and Processing of Nanocrystalline Powder, Proceedings of a Symposium, Anaheim, California, February 4th-8th, pp. 59-79. 

Description of the Existing and Improved Techniques of Diamond Nanopowder Synthesis... 

Liang J, Jiang X, Liu G, Deng Z, Zhuang J, Li F, Li Y (2003) Characterisation and synthesis of pure Zr02 nanopowders via sonochemical method. Mater Res Bull 38 161-168... 

Zhao, S. and Asuha, S. (2010) One-pot synthesis of magnetite nanopowders and their magnetic properties. Powder Technology, 197 (3), 295-297. 

MAS-NMR of 19 samples of GaN nanopowders also characterized by XRPD were prepared by 4 different synthesis methods, and some were subjected to various treatments [234]. It also provides a warning against the attempts to interpret measured chemical shift positions in nano-semiconductors without taking into account the possible contribution of Knight shifts. 

Fig. 13 69Ga MAS-NMR spectra of GaN nanopowders labeled by sample codes. Left Knight shift resulting from thermal annealing. Right three different samples produced by GaAs nitridation synthesis containing c-GaN (357 ppm) as well as h-GaN (326 ppm). The broad peak at 470 ppm is assigned to Knight shifts in c-GaN. Reprinted with permission from [234], Copyright 2008 by the American Chemical Society...

Bansal NP and Zhong Z. Combustion synthesis of Sm0 5Sr0 5Co03 x and Lao 6Sr04CoO3 x nanopowders for solid oxide fuel cell cathodes. J. Power Sources 2006 158 148-153. 

Laser pyrolysis has been shown to produce a wide variety of crystalline transition metal nitride and carbide nanoparticles with diameters as small as 2 nm. The nanopowders are in many cases monophasic and single crystalline. By varying the reaction conditions it is possible to control the particle diameter, and in some cases, the crystalline phase produced. Improvements in the synthesis are needed to control surface oxidation. 

I. Mohai, J. Szepvolgyi, I. Bertoti, M. Mohai, J. Gubicza, T. Ungar, Thermal plasma synthesis of zinc ferrite nanopowders, Solid State Ionics 141-142 (2001) 163-168. 

Micro- and nanociystalline materials possess unique properties in comparison with bulk materials of the same composition [1-6]. However, despite of significant advances in the synthesis of powders with tailored properties and the study of their structure and physicochemical characteristics, a number of questions remain open. The objective of this work is to investigate the oxidation behavior of silicon micro- and nanopowders prepared by different processes and to compare it with that of single-crystal Si. 

Djurado, E. and Meunier, E., Synthesis of doped and undoped nanopowders of tetragonal polycrystalline zirconia (TPZ) by spray pyrolysis, J. Solid State Chem., 141, 191, 1998. 

Keywords synthesis, high-silica zeolite, nanopowder, clusters, mesoporous... 

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