Nanoparticles nanostructured particles

Abstract. IR pyrolysis of PAN and PAN based composites yields ordered graphitelike structure as well as several carbon nanostructures. Metal-carbon nanocomposites, in which the nanosized metal particles were introduced into the structure of carbon matrix in the course of IR pyrolysis of composite-precursor on the basis of PAN and metal (Gd, Pt, Ru, Re) compounds were prepared. The carbon phase of metal-carbon nanocomposites was shown to include different types of nano structured carbon particles. Bamboo-like CNT were observed in the structure of pyrolized at 910 and 1000°C composite-precursor based on PAN and GdCl3. At T=1200°C the solid carbon spheres with diameter in the range of 50-360 nm and octahedral carbon particles with the size in the range of 300-350 nm were observed. These nanostructured particles consist of carbon only or they include Gd nanoparticles incapsulated in carbon shell. IR pyrolysis of composite-precursor based on PAN as well as H2PtCl6 and RuC13 or NH4Re04 (Pt Ru(Re)=10 l) allows the preparation of Pt-Ru and Pt-Re alloys nanoparticles with 2[Pg.577]

It is important to note that structural transformations of obtained bamboo-like CNT takes place while IR radiation intensity rises. At T=1200°C bamboo-like CNT are converted to solid carbon spheres with diameter in the range of 50-360 nm and octahedral carbon particles with the size in the range of 300-350 nm (Fig. 5). These nanostructured particles consist of carbon only or they contents Gd nanoparticles incapsulated in spherical or octahedral carbon particles. The mechanism of high temperature structural transformations of bamboo-like CNT still needs research. 

Tlie CVD method is usually used to produce a thin film material which is formed on a heated substrate. However, nanostructured particles of ceria and ceria-yttria have been synthesized by some arrangements of the apparatus. Figure 3.8 shows the schematic CVD reactors for synthesizing ceria-based nanopanicles.Two types of rector has been presented. The nanoparticles are collected either on a cooled quartz susceptor (A) that is in a furnace, or in a cold wall container outside the furnace (B), The precursor cerium chloride set on the container is evaporated and... 

Similar studies in an organic solvent yielded almost the same product [66]. Nanostructured particles of amorphous carbon-activated palladium metallic clusters have been prepared (in situ) at room temperature by ultrasound irradiation of an organometallic precursor, tris-//-[dibenzylideneacetone]dipalladium [(p-CH= CH-CO-CH=CH-5 )3Pd2] in mesitylene. Characterization studies show that the product powder consists of nanosize particles, agglomerated in clusters of approximately 800 A. Each particle is found to have a metallic core, covered by a carbonic shell that plays an important role in the stability of the nanoparticles. The catalytic activity in a Heck reaction, in the absence of phosphine ligands, has been demonstrated. 

It has been reported that Y2O3 nanoparticles as-prepared by gas phase synthesis have the monoclinic stmcture of high pressure phase, which transforms into cubic Y2O3 above 873 K [7,8]. It has been elucidated from the dependence of the phase transition temperature on the state of compaction that the stability of the high pressure phase is due to the nanostructured particle size. 

Iskandar, F., Gradon, L., Okuyama, K., 2003, Control of morphology of nanostructured particles prepared by the spray drying of a nanoparticle sol, J. Colloid Interface Sci. 265, 296-303. 

The effect of size quantization on the electronic properties of semiconductors, discussed in Section 9.2.2, demonstrates that semiconductor electrodes made of nanostructured particles are of great practical interest. Based on size quantization, these films can be categorized into (a) thin semiconductor films deposited or epitaxial growth on a substrate where the SQE is due to the space confinement in two dimensions (i.e., a quantum well) and (b) particulate films of size-quantized nanoparticles that may be several micrometers thick their properties are due to the combined effect of film and isolated size-quantized particles. Both the situations are illustrated in Figure 9.41. 

Maynard, A.D., Kuempel, E.D., 2005. Airborne nanostructured particles and occupational health. Journal of Nanoparticle Research 7 (6), 587-614. 

The last problem of this series concerns femtosecond laser ablation from gold nanoparticles [87]. In this process, solid material transforms into a volatile phase initiated by rapid deposition of energy. This ablation is nonthermal in nature. Material ejection is induced by the enhancement of the electric field close to the curved nanoparticle surface. This ablation is achievable for laser excitation powers far below the onset of general catastrophic material deterioration, such as plasma formation or laser-induced explosive boiling. Anisotropy in the ablation pattern was observed. It coincides with a reduction of the surface barrier from water vaporization and particle melting. This effect limits any high-power manipulation of nanostructured surfaces such as surface-enhanced Raman measurements or plasmonics with femtosecond pulses. 

In this chapter the potential of nanostructured metal systems in catalysis and the production of fine chemicals has been underlined. The crucial role of particle size in determining the activity and selectivity of the catalytic systems has been pointed out several examples of important reactions have been presented and the reaction conditions also described. Metal Vapor Synthesis has proved to be a powerful tool for the generation of catalytically active microclusters SMA and nanoparticles. SMA are unique homogeneous catalytic precursors and they can be very convenient starting materials for the gentle deposition of catalytically active metal nanoparticles of controlled size. 

Mossbauer spectroscopy has been extensively used for studies of nanostructured materials and several reviews on magnetic nanoparticles have been published, see e.g. [6-8, 46 8]. The magnetic properties of nanoparticles may differ from those of bulk materials for several reasons. The most dramatic effect of a small particle size is that the magnetization direction is not stable at finite temperatures, but fluctuates. 

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