Carbon/graphite-filled polymers

Garbon- or graphite-filled polymers or a carbon paste, which can easily be regenerated by removing a surface layer, are also possible electrode materials. 

The electrolyte is a perfluorosulfonic acid ionomer, commercially available under the trade name of Nafion . It is in the form of a membrane about 0.17 mm (0.007 in) thick, and the electrodes are bonded directly onto the surface. The electrodes contain very finely divided platinum or platinum alloys supported on carbon powder or fibers. The bipolar plates are made of graphite-filled polymer or metal. 

Carbon C (electrographite, Acheson graphite) Carbon black-filled polymers, graphite-filled plastics, graphite-felt, glassy carbon (anode only), porous carbon, poly-p-phenylene (synthetic metal)... 

Figure 9. Schematic representation of the effects of PTFE powders and TiOj-nanoparticles on the changes in the frictional coefficient and contact temperature of graphite and short carbon fiber-filled polymer composites.

These consist of a number of parallel slots cut into the concrete surface. Each slot is then filled with a secondary anode of carbon/graphite fibres embedded in a conductive polymer grout. The current to each of these secondary anode systems is provided by a primary anode of platinised niobium wire placed in slots filled with conductive polymer which acts as the primary anode, these slots intersecting each slot of graphite fibre/conductive polymer at right angles. 

Nonmetallic conductors and corrosion products. Carbon brick in vessels is strongly cathodic to the common structural alloys. Impervious graphite, especially in heat-exchangers, is cathodic to structural steel. Carbon-filled polymers can act as active cathodes. Some oxides or sulfates are conductors, such as mill scale (magnetite Fe304), iron sulfides on steel, lead sulfate on lead can act as effective cathodes with an important area to that of the anodes. Very frequently, the pores of the conductive film are the preferable anodic sites that leads to localized corrosion (pitting).5... 

W. Thongruang, C. Maurice Batik, J.S. Richard, Volume-exclusion effects in polyethylene blends filled with carbon black, graphite, or carbon fiber. J. Polym. Sci., Part B Polym. Phys. 40, 1013-1025 (2002)... 

For carbon nanotubes, discussed in detail in Chapter 10, conductivity is achieved at lower loadings (by weight) but these materials are difficult to disperse in molten polymers. Methods of surface functionalization and lower cost manufacturing must be developed before carbon nanotubes will find wider use as conductive fillers [52, 53]. As an alternative to nanotubes, Fukushima and Drzal [54] have observed conductivity thresholds of less than 3 vol% in composites containing acid-etched or othervdse functionalized exfoliated graphite. These composites retain or improve upon their mechanical properties compared to other carbon-filled polymers. 

Ticona has co-operated with SGL Carbon to produce a graphite-filled liquid crystal polymer, also for fuel cell plates. There are likely to be 200 bipolar plates for each cell, and two cells per vehicle. The filled polymer is meant to be injection moulded, but this requires much higher throughputs than compression moulding to be economic. 

Filled polymers are intrinsically nonconductive polymers loaded with conductive fillers such as carbon black, graphite fiber, metal particles, or metal oxide particles (5-9). Filled polymers have the longest history and broadest application in electronic devices. These materials have been used since the 1930s in the prevention of corona discharge and later in advanced printed circuitries. The extensive use of these materials hes in their ease of processing, wide range of electrical properties, and relatively low cost. However, these materials are inhomogeneous. 

Perhaps the largest volume commercial production of particle-filled polymers is carbon- or graphite-filled rubbers. Carbon blacks are widely used in natural and synthetic rubbers and convey significant improvements in modulus, abrasion resistance, and tear strength as well as additional thermal and electrical conductivity. Carbon blacks are uniquely efficient in these respects the reasons for this are still the subject of debate. A very recent review by Rigbi is an excellent compilation of current theory and experiment. An earlier review by Medalia ... 

Although Raman spectroscopy is very useful for identification and quantitation of carbonaceous species in various matrices, carbon is the most problematical filler. Common carbon fillers (amorphous coke or graphite) are strong Raman scatterers, but they also strongly absorb the Raman scattered light from the polymer. Thus, a carbon-filled polymer often displays only the spectrum of carbon, or if excessive laser power is used, the sample is burnt by laser absorption. When using 1064 nm excitation (FT-Raman) carbon-filled samples are strongly heated and will incandesce. 

The conductivity of the sample containing 0.05% PANI-CSA is approximately 10 S/cm, several orders of magnitude higher than the typical values of conductivity obtained in filled polymer composites containing similar volume fractions of carbon black [222-224 H. B. Brom, personal communication, 1994.) or graphite particles [225. 226]. Although percolation thresholds as low as0.1 vol % [222,223 H. B. Brom, personal communication] and 0.4 wt % [224] have been reported for carbon black/polymer composites, the conductivity near the percolation threshold for those samples is less than 10 S/cm. 

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