Ultrafine powders synthesis

Aerosol techniques on-line sizing of colloidal nanoparticles, 20-40 ultrafine powder synthesis, 64 Ag particles, synthesis method, 128 Aluminum nitride powder prepared via chemical synthesis, characterization using Fourier-transform IR spectroscopy, 312-332... 

Vapor-Phase Techniques. Vapor-phase powder synthesis teclmiques, including vapor condensation, vapor decomposition, and vapor—vapor, vapor—Hquid, and vapor—soHd reactions, employ reactive vapors or gases to produce high purity, ultrafine, reactive ceramic powders. Many nonoxide powders, eg, nitrides and carbides, for advanced ceramics are prepared by vapor-phase synthesis. 

Ultrafine powders are usually considered to be particles with diameters between 1 -100 run [141]. A focus for recent work in material chemistry has been the preparation of such particles [142] because of their special properties optical, photocatalytic, electrochemical, magnetic, thermal resistance, high melting point and sintering abilities [143,144]. A variety of chemical and physical methods have been used for the synthesis of such materials including the decomposition of organometallics [145] and the controlled reduction of salts [146-148]. 

Tsuzuki and McCormick have shown that suitably designed reduction reactions can also be used for the synthesis of ultraline oxide powders. In their study, ultrafine powder particles of Cr203 were prepared by the reduction of Na2Cr207 with sulfur. 

Fomin, VM., Cherepanov, A N. (1995), Plasma-Chemical Synthesis of Ultrafine Powders and Their Application for Modification of Metals and Alloys, Low-Temperature Plasma Series, Gukov, M.F. (ed.), vol. 12, Nauka (Science), Novosibirsk, Russia. 

Jia XL, Zhang HJ, Yan YJ, Liu ZJ (2004) Effect of the citrate sol-gel synthesis on the formation of MgAl204 ultrafine powder. Mater Sci Eng A-Stmct Mater Prop Microstmct Process 379 112-118... 

C. F. Yang and J. Y. Chen, Synthesis of stabilized zirconia ultrafine powders using AOT-isooc-... 

Chemically Synthesized Powders. Chemical synthesis provides a means of produciag powders for manufacturiag advanced ceramics. Disadvantages of chemically synthesized raw materials are expense and difficulties ia scale-up and availabihty. Additionally, ultrafine particle-size powders produced by chemical synthesis pose some unresolved processiag problems ia the areas of handling and mixing. 

Synthesis by means of volatile compounds A number of halides (especially chlorides) of the transition metals display a high volatility and in the gaseous state they are easy to mix. They can be synthesized from oxides, or scrap metals, and chlorine they are highly reactive and can be utilized for the preparation of various compounds, either as powder or a coherent solid or as coatings. Mixtures, for instance, of TiCLj + CH4 + H2 have been used to prepare ultrafine TiC powder, to deposit TiC on graphite (at 1200-1300°C), etc. 

Fig. 8.1.3 Rcaclor chamber designed for powder processing studies (1) torch head. (2) three concentric quart/ lubes. (3) work coil, (4) water-cooled Pyrex cylinder. (5) water-cooled copper quenching plate. (6) window, (7) to generator, (8) water in, (9) water out. (10) to exhaust system. (Reprinted front J Mater Sci, 65. The synthesis of ultrafine titanium nitride in an r.f. plasma. Copyright 1979. with kind permission from Kluwer Academic Publishers.)...

Kubo N, Futaki S, Shiraishi K (1987) Synthesis of ultrafine Si3N4 powder using the plasma process and powder characterisation. In Somiya S, Mitomo M, Yoshimura M (eds) Silicon Nitride I. Elsevier, London, p 93... 

Cao J., Li Z. Mechanically activated synthesis and apphcation of ultrafine ZrSi04 powder. Trans. Nonferrous Metal. Soc. China 1998 8 259-62. 

A great number of works on the aqueous synthesis of ceria NPs have been reported from very early years, since the ultrafine ceria powders are re-examined from fhe view point of nanotechnology for example, the simple precipitation methods (Zhang et al., 2002a), the microemulsion methods (Masui et al., 1997 Zarur and Ying, 2000), urea assisted hydro-thermal methods (Hirano and Inagaki, 2000 Hirano and Kato, 1999), hydrothermal methods with supercritical conditions (Adschiri et al., 2001). 

The microwave irradiation heating methods are facile, quick, and productive for synthesis of ceria NPs. Ultrafine crystalline ceria powder... 

Russian group of Derjaguin et al., by irradiating ultrafine graphite powder with a CO laser beam, and was later confirmed by Roy et al. Various other researchers have reported diamond synthesis by similar techniques (e.g., 24-27). Diamond formation by laser ablation of graphite too has been claimed (e.g., 28, 29). 

In preparing fine particles of inorganic metal oxides, the hydrothermal method consists of three types of processes hydrothermal synthesis, hydrothermal oxidation, and hydrothermal crystallization. Hydrothermal synthesis is used to synthesize mixed oxides from their component oxides or hydroxides. The particles obtained are small, uniform crystallites of 0.3-200 jim in size and dispersed each other. Pressures, temperatures, and mineralizer concentrations control the size and morphology of the particles. In the hydrothermal oxidation method, fme oxide particles can be prepared from metals, alloys, and intermciallic compounds by oxidation with high temperature and pressure solvent, that is, the starting metals are changed into fine oxide powders directly. For example, the solvothermal oxidation of cerium metal in 2-mcthoxycthanol at 473-523 K yields ultrafine ceria particles (ca 2 nm). 

Summary of Some Representative Examples of Mechanochemical Reaction Systems Developed for the Synthesis of Ultrafine Ceramic Powders... 

Dodd, A.C., Raviprasad, K., and McCormick, P.G., Synthesis of ultrafine zirconia powders by mechanochemical processing, Scripta Mater, 44, 689, 2001. 

Narisawa M, Okabe Y, Iguchi M, Okamura K (1998) Synthesis of ultrafine SiC powders from carbon-silica hybridized precursors with carbothermic reduction. J Sol-Gel Sci Technol 12 143-152... 

Jokanovic, V., Janackovic, Dj., Spasic, A.M., and Uskokovic, D., Synthesis and formation mechanism of ultrafine spherical AI2O3 powders by ultrasonic spray pyrolysis, Mater. Trans., JIM, 37, 627-635, 1996. 

The hydrothermal synthesis of ferroelectric nanoparticles like BaTiOs is an industrial concern. This method is a powerful tool for fabricating ultrafine, homogeneous powders of high purity for a large variety of multi-cation oxides [73] as compared to methods based on the decomposition of solid precursors. The main advantage of hydrothermal synthesis is the improved control of the chemical and granular... 

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