Carbon nanodispersion

Materials obtained by pyrolysis of pitch-polysilane blends have been extensively studied as carbon materials containing Si [157-161], For some of these materials, ca. 600mAh/g of Crev for Li insertion, as well as small irreversible capacities and small hysteresis effects, were reported. It has been shown that the materials contain nanodispersion of Si-O-C and Si-O-S-C instead of nanodispersed Si particles [162-165], Furthermore, the oxygen and sulfur contents are proved to be correlated to the irreversible capacity. There is a report about the fabrication of porous Si negative electrodes with 1-D channels, where the usefulness of the fabricated negative electrodes for rechargeable microbatteries is also suggested [166],... 

Wilson AM, Dahn JR. Lithium insertion in carbon containing nanodispersed silicon. J Electrochem Soc 1995 142 326-332. 

Wilson AM, Way BM, Dahn JR, van Buuren T. Nanodispersed silicon in pregraphitic carbons. J Appl Phys 1995 77 2363-2369. 

CIL is unavoidable when nanodispersion of any other nanofiller, such as clay or carbon nanotube (CNT) is considered [17,18], Various types of cationic surfactants in the case of montmorillonite (MMT) and reactive interface modifications in the case of CNT have been introduced to ensure... 

Composites, in the usual sense, were proposed to improve the mechanical stability of the electrode. An example is 80 wt% coke powder in PVC [192]. Of greater interest are carbons with nanodispersed boron (via BCI3, 900 °C). The compound B0.17C0.83 has a reversible specific capacity of 437 Ah/kg [193]. An even stronger enhancement of ilTs, up to 500 Ah/kg could be achieved by silicon (via SiCLj/via Me2Cl2Si, 950 °C) for the composition Si0.nC0.g9 [194,195]. Structural aspects are compiled in Fig. 22. The improved stoichiometry is attributed to the electron-acceptor capability of boron or silicon. Doping of petroleum-fuel green coke by phosphorus elevates by 20% [191]. 

Fig. 22. (a) Franklin s model for pregra-phitic carbon stacked graphene layers are represented by straight lines. Bent or 2.45 A curved lines represent tetrahedrally bonded carbon chains or buckled graphene layers. Tbe nanodispersed silicon atoms are represented as shaded dots. After Wilson and Dahn [194]. (b) Schematic drawing of the lithium sites on a single layer of boron-substituted carbon. The broken circle represents tbe site for additional lithium beyond jc = 1 in Lij((B2Ci z)6. After Dahn et al. [195]. 

The largest exchange current density, j0, of the reaction has to be selected, if possible, since economic limitations are always prevalent in scaled-up engineering. However, with the development of nanodispersed substrates and carbon-supported metal catalysts, this limitation becomes a secondary consideration. At this point, it is important to say that most of the reported values of j usually refer to simple reactions on pure metal substrates using different shapes of electrode designs in a certain and single electrolyte. Thus, the measurement of the real j0 value at select industrial conditions of the electrochemical reactor has to be performed that is, experimental measurements cannot be avoided [4,5]. 

Thus, the regioselectivity of the Heck reactions with unsymmetrical aikenes can favorably be manipulated by appropriate variations of the catalyst cocktail [123] for example, the best conditions for the couphng of bromobenzene with t-butyl acrylate in the presence of Pd[(o-Tol)3P]2Cl2 (Tol, tolyl) were found to be with potassium carbonate in ethanol at 80 °C. This is unusual for this kind of catalyst system. The active catalyst is actually believed to be nanodispersed palladium metal generated by reduction of the catalyst precursor by ethanol under basic conditions (Table 8.5). 

The comprehensive flame retardation of polymer-clay nanocomposite materials was reported by Dr. Jeff Gilman and others at NIST [7]. They disclosed that both delaminated and intercalated nanoclays improve the flammability properties of polymer-layered silicate (clay) nanocomposites. In the study of the flame retardant effect of the nanodispersed clays, XRD and TEM analysis identified a nanoreinforced protective silicate/carbon-like high-performance char from the combustion residue that provided a physical mechanism of flammability control. The report also disclosed that The nanocomposite structure of the char appears to enhance the performance of the char layer. This char may act as an insulation and mass transport barrier showing the escape of the volatile products generated as the polymer decomposes. Cone calorimetry was used to study the flame retardation. The HRRs (heat release rates) of thermoplastic and thermoset polymer-layered silicate nanocomposites are reduced by 40% to 60% in delaminated or intercalated nanocomposites containing a silicate mass fraction of only 2% to 6%. On the basis of their expertise and experience in plastic flammability, they concluded that polymer-clay nanocomposites are very promising new flame-retarding polymers. In addition, they predict that the addition... 

An appreciable increase in the utilization efficiency of platinum catalysts in fuel cells was attained when the highly dispersed platinum was deposited not directly onto the conductive electtode base but onto carbon black or other carbon materials serving as an intermediate base for the nanodispersed catalyst. On carbon supports, the nanosized platinum crystallites were less subject to recrystallization and coarsening. In addition, new technical devices such as adding Nafion ionomer to the active mass have helped to considerably improve the contact between catalyst and solid electrolyte (a Nafion-lype membrane). Carbon black was found to be a very convenient support for platinum catalysts. It is readily available and not expensive. Certain blacks (such as furnace black Vulcan XC-72) have special surface properties that have a favorable effect on catalyst activity. 

Harikrishnan, G., S. N. Singh, E. Kiesel, and C. W. Macosko. 2010. Nanodispersions of carbon nanofiber for polynrethane foaming. Polymer 51 3349-3353. 

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