Hollow carbon fibers

Types aluminum fiber, aluminum hydroxide, antimony trioxide, calcium caibonate, carbon black, carbon fiber, hollow glass beads, kaolin, magnesinm hydroxide, mica, sand, silica, silica carbide, talc, waste leather particles, wollastonite, wood fiber, wood flour, zeolite... 

Fig. 4. Coexisting vapour-grown carbon fiber, with thicker diameter and hollow core, and carbon nanolubes, with thinner hollow core, (as-grown samples).

The mechanical properties of the membrane are essential in operation and module design. For instance, hollow carbon fibers fabricated by pyrolysis of polymers are seemingly too brittle for practical applications [111]. Ceramic capillaries prepared by extrusion are much stronger, but appear limited in maximum length due to... 

Synthetic stocks are gradually replacing the traditional wooden stock due to their cheapness, ease of manufacture, lighter weight, and wear ability, and are claimed to be more stable and easier to maintain than wooden stocks. Materials such as nylon, polyurethane, fiberglass, Kevlar reinforced with fiberglass or carbon fiber, or thermoplastic resin reinforced with glass and ceramics may be used. The stocks may be hollow, or have a hollow filled... 

The transmission electron microscopy of the pyrolysis products (Fig. 4) shows the presence of carbon fibers having the outer diameter of 20-200 nm, and some of them, the thinnest, having hollow channel inside. The most of fibers are a kind of tightly curled helices or "plumed clouds". 

The main advantages of reactors with composite membrane catalysts arc the higher hydrogen permeability and smaller amount of precious metals in comparison with those presented in Section II. All constructions of the reactors with plane membrane catalyst may be used for composites of thin palladium alloy film and porous metal sheet The design of reactors with composite membranes on polymeric support may be the same as for diffusion apparatus with polymeric membranes (see, for example. Ref. 138). A very promising support for the composite membrane catalysts is hollow carbon fiber [139], once properly thermostable adhesives are found. 

Hollow BN fibers are made by depositing a coating of BN on carbon fibers, heating in an oxidizing atmosphere to form CO or CO2, and leaving a BN coating. The reaction between BF3 and NH3 at 1200-1400°C may be used . Yarn and BN/BN composites can be made with similar techniques (see 17.3.5.6). 

As mentioned in the previous section, hollow zeolite spheres of LTA, FAU, BEA, MFI can be prepared in the presence of polystyrene beads as templates by using an LBL self-assembly technique. Recently, several research groups have tried to adopt similar methods to synthesize zeolite-template composites on the surfaces of templates with various shapes and sizes, properties, and structures through self-assembly or in situ-crystallization approaches. Subsequent removal of the templates forms zeolite materials with analogical skeletons of the templates. Up to now, the reported templates include microspheres, carbon fibers, polyurethane foams, and microbe structures,[144,145] as well... 

Names nickel coated carbon fiber, steel fiber, powder, silver coated hollow and solid glass spheres, silver coated mica, silver coated fiber... 

Chemical composition variable composition silver coatings in Conduct-O-Fil solid glass spheres and fibers -4-16 wt%, 30% on hollow glass spheres, 65 wt% on mica flakes, 8-19 wt% on copper flakes, 24 wt% on nickel granules, 20 wt% on aluminum particles, nickel coating on Compmat carbon fiber is 24 wt%... 

Filament diameter, pm 4-7 (carbon fiber), 0.01 (hollow graphite fibrils), 10-13 (pitch-based)... 

Figure 2.78. A structure of hollow carbon fibers. Courtesy of Hyperion...

Decomposition of carbon bearing gases over transition metals often results in the formation of filamentous materials ("carbon fibers"). These carbon fibers are uniform in width, usually between 500-1000A, come in the shape of flat ribbons, solid or hollow tubes, and some are even twisted. The formation of these filaments results in corrosion of the metallic phase. 

Hollow fibers and spheres of zeolite (labeled as HFZ and HSZ, respectively) were successfully fabricated using carbon fibers and polystyrene (PS) spheres as templates respectively, through layer-by-layer technique, coupled with removal of the templates by calcination. The optimum performance conditions to obtain these kinds of materials were systematically studied. The wall thickness and composition of these novel materials can be readily tailored by varying the number of nanozeolite/PDDA (poly(diallyldimethyl ammonium chloride)) deposition cycles and zeolite type used, respectively. The properties of these novel materials were characterized by means of XRD, IR and SEM. 

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