Mechanical carbon onions

In HRTEM pictures of some samples of carbon onions, spiral patterns are observed that correspond to three-dimensional, nauhlus-like spiral objects. These are especially found as an intermediate in the generahon of concentric nanoonions from other forms of carbon. A more detailed discussion of these structures and their relevance is found in Section 4.3 on the mechanisms of onion formahon. 

Figure 4.12 Mechanism of the formation of carbon onions in a metai substrate.

Growth Mechanisms of Carbon Onions Obtained by Electron Irradiation... 

Figure 4.29 (a) Mechanism proposed for the formation of carbon onions via spiroid... 

There have been a variety of mechanisms suggested as contributors to the broadband EM attenuation displayed by OLC, including electrical conductivity that can be tuned by the hierarchical assembly of the primary carbon onion particles and inner shell defects." It has been observed that... 

FIGURE 12.15 Proposed self-assembly mechanism of mesoporous carbon-onion-like carbon nanocomposites ( brick and mortar ). The onion-like carbon as well as other carbon nanostructures such as CB is dispersed in the final OMC framework, whereas a mesoporous OLC framework bound by a thin carbon film from the resorcinol-formaldehyde carbon is obtained in excess of the nanoparticles (a). Calculated PSD curves (b) for OLC and CB/OMC nanocomposites. The mesopore diameters increased with increasing OLC and CB contents. (From Fulvio, P. F. et ah, Advanced Functional Materials, 21, 2208, 2011. With permission.)... 

Ozawa et al. proposed another growth mechanisms of carbon onions based on TEM observations of carbon black irradiated by an electron beam [13]. Spiroids are first formed and then carbon onions (Figure 3.3). Qin and lijima also studied the formation of spheroid graphitic particles by irradiating diamond crystals inside a TEM [14]. Since the mechanism of carbon onion formation was not known, several studies were carried out to follow the transformation of diamond nanoparticles into carbon onions directly inside a transmission electron... 

Figure 3.3 Growth mechanism of carbon onion from spiroid proposed by Ozawa et al. Reproduced by permission of American Chemical Society from Ozawa et al. [13], Figure 3, (2002) American Chemical Society...

Other carbon nanoparticles may also present interesting tribological properties nanohorns [122], peapods (nanotubes filled with Ceo) [123] and C70. Furthermore, the study of their tribological properties may also lead to a better understanding of the lubrication mechanism of carbon nanotubes and carbon onions. 

Ding, L. et al. (2005) Molecular characterization of the cytotoxic mechanism of multiwall carbon nanotubes and nano-onions on human skin fibroblast. Nano Letters, 5 (12), 2448-64. 

Fig. 7.28 Erosive dispersion of a carbon black agglomerate in butadiene rubber (BR) in simple shear flow, showing (a) the onion peeling mechanism, (b) a ribbon peeling mechanism and (c) both mechanisms. [Reprinted by permission from M. Astruc, Etude Rheo-optique des Mecanismes de Dispersion de Melanges sous Cisaillement Simple 1. Melanges concentres de polymeres immiscibles, 2. Melanges polymeres-charges poreuses, Doctoral Dissertation, Sophia Antipolis, Ecole des Mines de Paris, France (2001).]...

During the late afternoon when the vapor pressure gradient declines, ponderosa pine stomata may open wider, resulting in greater oxidant uptake and simultaneous depression of carbon dioxide fixation. Some knowledge of stomatal function would be useful to see if there is any relationship between intraspecific oxidant tolerance and ability to close stomates in the presence of elevated ozone concentrations. This mechanism is an inherited characteristic of an ozone-resistant onion variety which closes its stomates when exposed to ozone (30). It is not known if this mechanism is involved in conditioning interspecific tolerance or sensitivity of the important conifer species. 

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