Carbon fiber paper manufacturing

It is also important to take into account that one of the main issues with the carbon fiber paper or cloth used as the DL is the uncontrolled variation in porosity (and other localized properties) of these manufactured conventional diffusion layers that is, the porosity characteristics between carbon papers are not repeatable [57]. These materials are difficult to improve because only average pore sizes and volume densities can be measured and much of the development has been based on empirical parameters. Thus, extensive work has focused on optimizing the MPL in order to reduce the differences within carbon paper fiber and cloth diffusion layers. 

Through-plane permeability is usually one of the most common parameters given by manufacturers for carbon fiber papers and carbon cloths, even though it is often not specified as through-plane permeability. It is important to note that commercial instruments, such as permeameters and Gurley method instruments, are used in the fuel cell industry to measure this permeability [197,218]. 

These tests were performed on materials with the same characteristics but with different thicknesses thus, the intrinsic thermal conductivity could be resolved at different temperatures and compression pressures. Through these tests, the thermal conductivity of TGP-H carbon fiber papers was measured and achieved the same value as that reported by the manufacturer. In addition, it was observed that the thermal conductivity of the CFPs decreased from 1.80 + 0.27 W m i K i (af 26°C) to 1.24 + 0.19 W m-i K i (at 73°C). This result was suggested to be due to the presence of carbonized thermosetting resin on the CFPs. The thermal conductivity of fhe resin, which is a thermosetting polymer and acts as a binder, decreases with increasing temperature. For carbon cloth (without any resin), no significant changes in thermal conductivity were noted when the temperature was increased. 

The data on the mechanical properties of PTL materials are sparse. Mathias et al. reported on the compressive deflection as a function of compressive force for carbon fiber paper and carbon cloth materials (no specifications on material composition or manufacturer were provided) (Mathias et al., 2003). The maximum applied load was 2.75 MPa and the maximum compressive strain was approximately 23% and 53% for the fiber paper and cloth samples, respectively. Significant but decreasing hysteresis was observed on both materials after 10 cycles (from zero to maximum load). 

These somewhat conflicting requirements are best met by carbon fiber-based materials such as carbon fiber papers and woven carbon fabrics or cloths. Table 4-3 shows the properties of typical gas diffusion layers made of carbon paper and carbon cloth, as reported by various manufacturers. 

Baillie, C.A., Castle, J.E., Watts, J.F. and Bader, M.G. (1991). Chemical aspects of interface adhesion between electrolytically oxidised carbon fibers and epoxy resins. In Proc. ICCMI8, Composites Design, Manufacture and Application. (S.W. Tsai and G.S. Springer, eds.), SAMPE Pub. Paper HE. 

The different manufacturing techniques for highly specialized carbon products (i.e., isotropic coke, glassy carbon, and carbon fiber) are not covered by this paper. Moreover, a discussion of the multiplicity of testing methods used to study the carbonization behavior of different feedstocks and to characterize different coke qualities is also beyond the scope of this presentation. 

Our previous papers [15,16] and the current work show that die imprinting of mesophase pitch particles with colloidal silica is an efficient technique to prepare mesoporous carbons with uniform spherical pores as well as carbons with bimodal pore size distributions. These carbons exhibit negligible amount of micropores, which can be further eliminated during graphitization process. If micropores are need, they can be created by controlled oxidation analogous to that used in the preparation of activated carbon fibers. The possibility of tailoring the size of uniform spherical mesopores is of great importance for catalysis, adsorption and other advanced applications such as die manufacture of hi -quaiity electrochemical double-layer capacitors, fuel cells and lidiium batteries. 

Similar to the Types la and lb fibers, the Type Ic fibers consist of a thin, conductive metal layer electrodeposited upon a carbon base fiber (see Figure 5). Their manufacture is described by Morin(27) and by HaU and Ando(25). The paper by Hall and Ando provides a good overview of their properties and characteristics. Nickel plated exPAN carbon fiber are typical of the Type Ic fibers that are readily commercially available. General uses for Type Ic fibers are in ESI shielding, conductive adhesives and paints, conductive fabrics, and high performance electric contacts(2P). They are included in the Type 1 category because their conductivity is characteristically metallic. Thus, by this convention they appear in the Type 1 classification while the various other carbon fibers fall into the Type 2 category. 

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