Carbon foams

Synthetic Resins. Various polymers and resins are utilized to produce some specialty carbon products such as glassy carbon or carbon foam and as treatments for carbon products. Typical resins include phenoHcs, furan-based polymers, and polyurethanes. These materials give good yields of carbon on pyrolysis and generally carbonize directly from the thermoset polymer state. Because they form Httle or no mesophase, the ultimate carbon end product is nongraphitizing. 

The open ceU stmcture of carbon foam with its greater than 90% porosity and chemical inertness at temperatures below 500°C suggests its use as a filtration media for corrosive Hquids and a dispersant for gases. 

Product Hterature on KURASHEET activated carbon foam sheets, Kuraray Chemical Co., Ltd., Japan, 1987. 

If the composite is left only partially densified, it can be used as a filter for high temperature filtering systems with high collection efficiency as required in direct coal-fired gas and steam turbines. Similar systems are considered for particulate filtering in diesel engines by a carbon foam or felt coated with silicon carbide by CVI. 

Fig. 4.29 Immobilization of glucose oxidase in mesocellular carbon foam for a sensitive and fast glucose biosensor. Adapted from [226], D. Lee et a ., Adv. Mater. 2005, 77, 2828.

Huckins, J.N., D.L. Stalling, and J.D. Petty. 1980. Carbon-foam chromatographic separation of non-o,o -chlorine substituted PCBs from Aroclor mixtures. Jour. Assoc. Off. Anal. Chem. 63 750-755. 

Ketec cell Eltech Vertical metal (or carbon) foam electrodes in a tank Discontinuous cathode steel (chemically stripped for reuse carbon No ... 

The major issue found in testing is the corrosion of the foam material and resultant contamination of the membrane. The high manufacturing cost of the metal or carbon foam with the required pore shape, size, and distribution also is a challenge. Further study and testing of the corrosion mechanism, selection of appropriate coating, a capillary process involved in the tiny pores, and related water retention are necessary to identify whether the new material and concept can be finally applied in the plate. 

Blowing agents swell a thick carbon foam which envelopes the object in a heat-resistant layer... 

Suspended particles may consist of complex inorganic hydroxides and silicates or, sometimes, organic debris. Particles too small to be easily distinguished can cause difficulties when a drink is carbonated, acting as minute centres of instability resulting in a loss of carbonation, foaming (gushing) at the filler-head and variable fill volumes. 

These are produced by carbonizing foams made from various binders and micro-spheres. The binders include polyurethane1), resol1121 and novolac39) phenolic oligomers, and epoxy oligomers39), while glass 38), carbon 39), and ceramic 18) micro-spheres fillers have been used for carbonized foams. 

Fig. 8. Effect of molding pressure P on the stress in compression (crc) for a carbonized foamed plastic made from a compound binder (wood resin, furfuryl alcohol, maleic anhydride) and phenolic microspheres 381...

However, the syntactic materials with the lowest apparent densities are the carbonized foamed plastics. During the carbonization of these materials open pores are formed (see Fig. 9) which lead to a whole series of valuable properties such as strength, low heat conductivity, and controllable gas and water permeability (Table 15)39). 

Table 23 shows the thermophysical properties of some syntactic foams 2). Polyimide syntactic foams have a thermal expansivity of 20 xio-6 deg-1 and thermal conductivities of 0.085 W/mK at 22 °C and 0.111 W/mK at 370 °C 10S-106). The low thermal conductivity of the carbonized foams (Fig. 17) is due to their open pore structure113). 

Kent BL, Mutharasani R (1992), Cultivation of animal cells in a reticulated vitreous carbon foam, J. Biotechnol. 22 311-328. 

Foamed carbon is also nongraphitizable. The cell structure of the polymer foam remains intact upon careful carbonization and densities lower than 0.1 g/cm- are obtainable. The thermal conductivity is just above that of plastic foams, but foamed carbon can be used at much higher temperatures. Its relatively low compressive strength can be increased by impregnation with pyrolytic carbon, although the thermal conductivity increases at the same time. By comparison with glassy carbon, foamed carbon is easy to work, so that the shape does not have to be established at the start of the process. Foamed carbon is corrosion resistant, as are all carbon modifications. 

Retec cell with vertical metal or carbon foam cathodes. The cell performance is achieved mainly by high electroactive area. The cathode product is removed by dissolving or is used as anodes. 

J. Lee, K. Sohn, and T. Hyeon, Fabrication of Novel Mesocellular Carbon Foams with Uniform Ultralarge Mesopores. J. Am. Chem. Soc., 2001, 123, 5146-5147. 

Klett, J., Hardy, R., Romine, E., et al. (2000). High-thermal-conductivity, mesophase-pitch-derived carbon foams effect of precursor on structure and properties. Carbon, 38, 953—73. 

Further work on these remarkable materials involved their carbonization and the thorough characterization of the ensuing carbon foams [53], as well as their subsequent chemical activation, which produced a dramatic increase in surface area, reaching 1800 m2g when ZnCl2 was used as promoter [54]. 

Carbon nanofibers are filamentous cylindrical or conical structures formed of various arrangements of stacked graphene sheets (as cones or cups), with a diameter ranging from one to several hundred nanometers, and lengths ranging from 1 pm to several millimeters. Nanostructured carbon foams... 

The solubility of COz in crude oil or formation water has a distinct advantage in fracturing operations. C02 is stored until fluid recovery begins, and as the pressure decreases, gaseous C02 breaks out of solution and expands to push fluids to the surface. These properties allow C02 to remain in the formation for several hours prior to flowing the well back. However, if the carbonated foamed fluid is left in formation for an extended period of time, then the C02 will dissipate. 

The efficiency of the automotive proton exchange membrane (PEM) fuel cell is dependent on many factors, one of which is the humidification of the inlet air. If the inlet air is not sufficiently humid (saturated), then the stack can develop dry spots in the membrane and efficiency and voltage will drop. Therefore, it is necessary to ensure that humid inlet air at the proper elevated temperature is supplied to the stack. Current methods involve utilizing a spray nozzle to atomize water droplets onto a cloth or wire mesh substrate. As the ambient inlet air passes over the cloth it picks up moisture however, the relative humidity drops as the air is heated in the fuel cell. If heat could be supplied to the water efficiently, the system would become independent of the ambient conditions, the inlet air could become more humid at the proper temperatures, and the overall stack could maintain a high level of efficiency. Previous work with power electronic heat sinks and automotive radiators has demonstrated the high efficiency of carbon foam for heat transfer. Utilizing the carbon foam in the PEM fuel cell may reduce the inlet air humidification problems. 

It was shown that carbon foam is beneficial to humidification systems for fuel cells. The foam has demonstrated the ability to utilize waste heat from power electronics to both heat and humidify ambient inlet air to 80°C and 80% relative humidify. 

Pores can also be classified on the basis of their state, either open or clo.sed. In order to identify the pores by gas adsorption (a method which has frequently been used for activated carbons), they must be exposed to the adsorbate gas. If some pores are too small to accept gas molecules they cannot be recognized as pores by the adsorbate gas molecules in other words, these pores are closed pores for the gas used. These pores are called latent pores and include closed pores. Closed pores are not necessarily in small size. Thus, when carbon foam was prepared by the impregnation of poly(imide) into a poly(uTethatie) foam followed by carbonization, large macropores, few millimeters in size, were formed in the center of a block of foam, which gave the advantage that the loam can float on water [2]. 

Carbon foams were also prepared by impregnating poly(amide acid) into poly(urethane) foams used as template, followed by imidization and carbcmization [2]. The foams were tested as adsorbents for atmospheric humidity and also as supfmrts for anatase-type TiOi photocatalysts. In Fig. 47, clmnges in pore morphology with impregnation of poly(imide) and carbonization at 1273 K are shown. 

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