Carbon black, accessible surface area

The irmnersion enthalpies of the four activated carbons and of a graphitised carbon black (V3G, surface area 59 m g ), which is used as referraice to obtain the accessible surface area... 

Nonmetal electrodes are most often fabricated by pressing or rolling of the solid in the form of fine powder. For mechanical integrity of the electrodes, binders are added to the active mass. For higher electronic conductivity of the electrode and a better current distribution, conducting fillers are added (carbon black, graphite, metal powders). Electrodes of this type are porous and have a relatively high specific surface area. The porosity facilitates access of dissolved reactants (H+ or OH ions and others) to the inner electrode layers. 

Nowadays synthesis of mesoporous materials with zeolite character has been suggested to overcome the problems of week catalytic activity and poor hydrothermal stability of highly silicious materials. So different approaches for the synthesis of this new generation of bimodal porous materials have been described in the literature like dealumination [4] or desilication [5], use of various carbon forms as templates like carbon black, carbon aerosols, mesoporous carbon or carbon replicas [6] have been applied. These mesoporous zeolites potentially improve the efficiency of zeolitic catalysis via increase in external surface area, accessibility of large molecules due to the mesoporosity and hydrothermal stability due to zeolitic crystalline walls. During past few years various research groups emphasized the importance of the synthesis of siliceous materials with micro- and mesoporosity [7-9]. Microwave synthesis had... 

The morphology of a filler, such as carbon black, is usually well estimated by its specific surface area accessible to the rubber molecules and by its density. 

In a further work, Tang and Curtis26 have studied the influence of the tyre components by replacing coal with model compounds 4-(l-naphthylmethyl)-bibenzyl (NMBB), dibenzothiophene and 5-methyl-8-(l-methylethyl)dibenzo-thiophen-4-ol (MMDH). Carbon black was active for the NMBB hydrocracking, whereas little activity was found with SBR, waste tyres and waste tyre liquefaction residues. However, when the latter residues were previously heat treated to remove organic coatings and recover the carbon black component, significant NMBB conversions were observed. Moreover, both carbon black and heat-treated residues were active for the hydrodesulfurization of dibenzothiophene and MMDH, particularly when combined with Mo naphthenate and S. These results confirm the catalytic properties of carbon black in coal-tyre coliquefaction, provided that its surface area is accessible. 

Pt-doped carbon aerogels have been used successfully in the preparation of cathode catalyst layers for oxygen reduction reaction (ORR) in PEMFC systems [83-86]. Thus, different Pt-doped carbon aerogels with a Pt content of around 20 wt% were prepared by impregnation [83]. Results obtained with these Pt catalysts were compared with others supported on carbon blacks Vulcan XC-72 and BP2000, which are commonly used as electrocatalysts. The accessibility of the electrolyte to Pt surface atoms was lower than expected for high-surface-area... 

The presence of micropores in carbon materials usually facilitates metal dispersion, which does not, however, translate into an increase in the catalytic activity. This may be explained by the blockage of metal nanoparticles in micropores, which are not accessible to reagents [98]. As a consequence, PEMFC specifications require that carbon materials used in PEMFCs comprise a high contribution level of mesopores, but no micropores. The ratio of the surface area of mesopores (the external surface area) to the overall pore area may be characterized by the Actab bet ratio, where Actab is the surface area measured using cetyltrimethyl-ammonium bromide. It has been shown that carbon blacks with a Actab/Abet... 

CS as complex adsorbents include both accessible carbonaceous deposits and patches of a matrix. Therefore, the adsorption characteristics of CS depend on the ratio of areas of two types (or more phases) of the surfaces. During adsorption, various types of molecules can be predominantly adsorbed either on the matrix or on carbon components of the surfaces of hybrid particles (Gun ko and Leboda 2002, Gun ko et al. 2002c). Carbon deposits can have a structure similar to that of carbon black therefore, the latter is analyzed later. 

Denoyel et al. (1993) proposed a method to assess the total area of microporous carbons by immersion calorimetry. It was based on the assumption of the existence of a direct relationship between the enthalpy of immersion and the total area of the solid accessible to the wetting molecules. They used a non-porous carbon black (Vulcan 3) as a reference material to obtain the area enthalpy of immersion, Afijmn, (J m ), of a carbonaceous surface into different liquids. In this way, and considering that the enthalpy of immersion is simply proportional to the surface area available to the immersion liquids, irrespective of its external or microporous character, and whatever the size and shape of the micropores, they obtained the surface areas available to the different liquids using Equation (4.11). 

In a further study, a series of CMS was prepared from coconut shells by carbonization and activation with carbon dioxide (De Salazar et al., 2000). This series was characterized by carbon dioxide adsorption at 273 K and by immersion calorimetry using liquids with different molecular sizes, dichloromethane (0.33 nm), benzene (0.37 nm), cyclohexane (0.48 nm), 2,2-dimethylbutane (0.56 nm) and a-pinene (0.7 nm). Immersion data were analyzed following the two methods described above. A graphitized carbon black, V3G, with a BET surface area of 62 m g (N2,77 K), was used as a non-porous reference to obtain the area enthalpy of immersion of a carbonaceous surface into the different liquids. With these values, and the enthalpies of immersion of the CMS into the dilferent liquids, the surface areas accessible to the liquids were obtained. These are plotted in Figure 4.50 as a function of the molecular dimension samples are identified by a number that indicates their activation time (De Salazar et al., 2000). 

Table 5.3 contains the micropore volumes of selected samples, determined by application of the DR equation to CO2 adsorption data at 273 K, as well as the surface area accessible to dichloromethane, evaluated from the immersion enthalpy measurements and using a graphitized carbon black (V3G) as a non-porous reference. The CO2 adsorption at 273 K, on the PS char, was lower than the other oxidized samples, and its surface area, as measured by immersion into dichloromethane, was almost zero, thus indicating the very narrow microporosity developed in this char (see also De Salazar et al., 2000). 

Denoyel et al [4] proposed a different approximation focused on the determination of the surface area of porous materials fi om immersion calorimetry measurements. It is based on geometrical considerations so that they conclude that the immersion enthalpy is proportional to the surface accessible to the liquid probe and that it is independent of the shape and size of the ptores. The areal enthalpy of immersion, hi (J.m ), for a non-porous carbon black into each wetting liquid is used as reference to determine the surface area wetted hy the liquid probe in a porous carbon. 

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