Nanosized Powder

R.A. Vatin, Ch. Chiu, Z. Wronski, A. Calka, The effects of oxidized and oxide-free boron on the Mg-B-H nanohydrides transformation in the nearly nanosized powders . Solid State Phenom. 128 (2007) 47-52. 

Sometimes nanosized powders are also referred as ultrafine (UF) powders with an equivalent size of 10 to a few hundred nanometers. The commonly employed fuels for explosives, propellants and pyrotechnics are aluminum (Al), magnesium (Mg) and boron (B). However, the share in terms of quantity consumed is maximum for aluminum. 

Flame processes have been widely used to synthesize nanosize powders of oxide materials. Chemical precursors are vaporized and then oxidized in a combustion process using a fuel/oxidant mixture such as propane/oxygen or methane/air [190]. They combine the rapid thermal decomposition of a precursor/carrier gas stream in a reduced pressure environment with thermophoretically driven deposi-... 

Chiorino, A. Ghiotti, G. Prinetto, F. Carotta, M. C. Gnani, D. Marinelli, G., Preparation and characterization of Sn02 and MoO -Sn()2 nanosized powders for thick film gas sensors, Sens. Actuators B 1999,58, 338-349... 

The complex anion [HPT C WnC ci]4- has IR bands at 630 and 690 cm"1, assigned as vs, vas (respectively) of the Ti(02) unit.33 The Raman spectra of aqueous sulphuric acid solutions containing titanium indicate the presence of Ti(OI 1)2(804)2(1120)22, 34 The Raman spectrum of a well-characterised TiP207 catalyst has v, of TiOe at 620 cm-1, with v6 at 275/240 cm"1 (together with P03 and P-O-P modes.35 IR and Raman spectroscopy were used to characterise Ti02 nanosized powders formed by TiCl4 laser pyrolysis.36... 

Preparation and characterisation of W0i/Sn02 nanosized powders for thick films gas sensors... 

Also, in the study of Peng et al. [369], the mesoporous titanium dioxide nanosized powder was synthesized using hydrothermal process by applying cetyltrimethylammonium bromide as surfactant-directing and pore-forming agent. They synthesized and applied this nanoparticle for the oxidation of Rhodamine B (see Table 6). 

As compared to materials produced by traditional ceramic technologies using micrometer-sized powders, ceramics prepared from nanosized powders usually have different characteristics a dense ceramic with a submicron stracture is synthesized from nanopowders at relatively low temperatures (1100-1300 °C) and has a higher strength and a larger electroconductivity. 

Biomedical, pharmaceutical, and cosmetic applications account for 18%. Sunscreens use nanosized powders of TiOi or ZnO. 

Nanotechnology is a hot research topic. The field is trendy, popular, and high-tech. Although silica and iron oxide nanoparticles have a commercial history spanning half a century or more it is really only within the plast 15-20 years that technologies have been developed for producing ultrapure nanosized powders of a range of ceramics. The... 

The market for nanosized powders is much smaller than for conventional ceramic powders, but the cost per kilogram is much higher. Despite progress in scaling up production and reducing costs, nanosized powders remain relatively expensive (often 100 times more than conventional ceramic powders). 

TABLE 37.5 Current and Emerging Applications for Nanosized Powders ... 

Chow et al. [22] used spray drying to prepare nanosize hydroxyapatite (HA) particles. They used a nozzle to spray the acidic calcium phosphate solutiou aud an electrostatic precipitator to collect nanosize powder. Their high-resolution transmission electron microscopy (TEM) showed that the particles, some of which were only 5 nm in size, exhibited... 

Reports on man-made diamond obtained by HPHT synthesis were first published in 1955 by General Electric [4]. Usually, metals able to dissolve carbon under HPHT conditions are used as catalysts and increase growth rates. Diamond crystals of several millimeters in size can be obtained in this way, but usually small grains for abrasives are produced. Direct conversion of graphite to diamond without catalyst in HPHT apparatus is possible, but uneconomical for industrial application. Direct transformation can be done by the detonation method and produces nanosized powders of diamond and diamond-like carbon [5]. 

It has been demonstrated that freeze-diying could play an important role in the synthesis of high quahty Nd YAG nanosized powders [169]. Submicronic neodymium-doped YAG (Y3AI5O12) powder was synthesized from freeze-dried precursors. The powder calcined at 1200 °C, with small crystallite size and the lowest amount of organic residues, showed the highest sinterability. With these powder, although color centers were detected by transmission, transparent ceramics were obtained after a vacuum sintering at 1700 °C for 3 h and completed with a HIP treatment at 1700 °C, 160 MPa of Ar for 90 min. 

A simple and feasible repeated annealing process was available to obtain transparent PLZT(9/65/35) ceramics [226]. The experiment was started from nanosized powder of PLZT, which was synthesized directly from commercially available constituent oxides by using a high-energy ball milling at near room temperature. Transparent PLZT ceramics were obtained by annealing the samples... 

Metallic powders have a vast range of applications in chemistry [51]. Amongst these lie their use in catalysis [52] and organometalKc chemistry [53, 54). However, whilst larger particles are readily available, until now the preparation of nanosized powders has been difficult and expensive, Kmiting their commercial viability. 

Structural and Morphological Peculiarities of Silicon, Boron, and Aluminum Nitrides - Nanosized Powders... 

Some advantages associated with each of these spray pyrolysis techniques for producing ceramic powders are given by the SAD method published by Xia et al., which focuses on a strategy of separation of nanocrystals contained in powder particles using some compounds (salts) which melt under maximal temperature of sohd-state particle consoUdation. The melted salts resemble eutectic mixture chlorides and nitrates of Li, Na, and K distributed on the nanocrystallite surfaces and they are prevented from agglomerating. After their removal, by washing the obtained powders, it is possible to get, finally, nanosized powders in different systems [19-26]. 

It can be expected that size effects of all physical properties, sensitive in the bulk samples to external hydrostatic pressure, can be rendered to nanogranular ceramics or nanosized powders in terms of surface tension. The distribution of nanoparticles sizes in real materials has to result in the smearing of observed physical properties. This is illustrated in Fig. 2.25 on the example of Raman scattering spectra for PCT ferroelectric films. It is seen that with the particles size increase the lines of different vibration modes increase their intensity, decrease the width and shift. Since maximal... 

The nanosize powders of CoFe204 (average particle size 30 nm) [129] and NiFc204 (5-30 nm) [130] do not change their grains sizes even after annealing at temperatures 450 and 400 °C, respectively. The sol-gel method is the main synthesis technique for cobalt ferrite doped with Mn [131], Cr [132], Bi [133], Y, La [134], Gd, Nd [135] and Zn [136]. The sol-gel method has been very attractive... 

Shantha, K., Varma, K.B.R. Characterization of fine-grained bismuth vanadate ceramics obtained using nanosized powders. J. Am. Ceram. Soc. 83(5), 1122-1128 (2000)... 

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