Chemical carbon fibres

PTFE, known under the trade names Teflon and Fluon, is resistant to all chemicals, except molten alkalies and fluorine, and can be used at temperatures up to 250°C. It is a relatively weak material, but its mechanical strength can be improved by the addition of fillers (glass and carbon fibres). It is expensive and difficult to fabricate. PTFE is used extensively for gaskets and gland packings. As a coating, it is used to confer non-stick properties to surfaces, such as filter plates. It can also be used as a liner for vessels. 

Two commercial coal-tar-pitch-based carbon fibres, which were supplied by Osaka Gas Co., Ltd. (Osaka, Japan), have been used as starting materials. In the course of their synthesis, these CFs had been carbonised at different temperatures Tc = 1273 K (Donacarbo S-241) and Tc = 973 K (Donacarbo SL-242). The carbon fibres have been chemically activated with KOH and NaOH (Panreac Chemicals, Barcelona, Spain) at 1023 K under a N2 gas flow. More details concerning the activation conditions can be found elsewhere. Two different kinds of furnaces have been used for the activations. For laboratory synthesis a horizontal tube furnace is used which is capable of activating about 2 g of raw fibres per activation process. For the scale-up production approach an industrial chamber furnace is used. Thereby the amount of initial material could be increased by more than one order of magnitude up to 30 g per activation process. 

Macia-Agullo JA, Moore BC, Cazorla-Amoros D, Linares-Solano A. Influence of carbon fibres crystallinities on their chemical activation by KOH and NaOH . Micropor Mesopor Mater 2007 101 (3) 397-405. 

Cattanach, J.B., Harvey, R.C. Roll Forming of APC PEEK/Carbon Fibre Composite (1984) Application Note by Imperial Chemical Industries PLC, Welwyn Garden City (England), June 14, 1984... 

Carbon fibres are made by carbonizing or pyrolyzing polymer fibres. I came across the chemical aspects of this process in the book Principles of Polymerization by G. Odian in which the author describes how these fibres are made of polyacrylonitrile (PAN) a polymer which is represented in figure 14.4 (see also chapter 3). 

Before explaining the construction procedure, we have to warn about the importance of the carbon fibre choice. These fibres are produced by high temperature pyrolysis of polymeric materials. Nevertheless, it has been reported that their physical and chemical properties depend on the manufacturing procedure. In our works, the carbon fibres (nominal diameter of 7.5 im) used were supplied by Donnay (Belgium). Therefore, our procedures and results would be unsuitable for other carbon fibres. 

A study of the hydrophilic sites on the surface of activated carbon fibres has been made recently by Kaneko et al. (1995) with the aid of X-ray photoelectron spectroscopy (XPS). In this work cellulose (CEL)- and polyacrylonitrile (PAN)-based activated carbon fibres were used and samples were either chemically treated with H202 or heated in H2 at 1000°C. As expected, surface oxidation by the H202 treatment increased the initial uptake of water, while the H2 reduction caused a marked decrease in the amount of water adsorbed at low p/p°. Measurement of the peak areas of the XPS spectra provided a means of determining the fractional surface coverage by the hydrophilic sites. In this way a linear relationship was found between the low-pressure adsorption of water vapour and the number of hydrophilic sites (mainly —COOH). 

In recent years, several designs of rotor made from carbon-fibre reinforced plastic have come on to the market, combining strength, lightness and some resistance to chemical corrosion. Most rotors, however, are made of aluminium or titanium alloy. 

A more recent study has been made of the surface reactivity of several carbon fibres towards gaseous adsorbents. Heats of adsorption for water and for various organic gases were found not to vary significantly, but calculated adsorption coefficients showed that pre-oxidation enhanced the adsorption of polar adsorbates such as water, pyridine, and aniline. Kipling et a/. have shown that pre-treatment by oxygen can result in preferential adsorption of more polar components of a binary mixture. Care must be exercised, however, in that different surface complexes may promote specific adsorption of individual chemicals. ... 

Chemical vapour infiltration (CVI) is an extension of CVD processes only when a CVD process occurs on an internal surface of a porous substrate (especially for the fibre preform). As compared with CVD, the CVI process for ceramics is much more effective and important because it is the optimal technique to fabricate fibre reinforced ceramics and particularly carbon fibre reinforced carbon and advanced ceramic matrix composites. Both CVI and CVD techniques share some common features in overall chemistry, however, the CVI is much more complex than the CVD process in mass transport and chemical reactions. 

Figure 3.33. Functionally gradient coating on the carbon fibre [61] (a) microstructure and (b) chemical composition distribution...

Macia-Agull6, J.A., Moore, B.C., Cazorla-Amords, D., and Linares-Solano, A. (2004). Activation of coal tar pitch carbon fibres physical activation vs chemical activation. Carbon., 42, 1367-70. 

The immobilisation of antibacterial coatings onto conductive materials such as stainless steel or carbon fibre used in orthopaedic implants was investigated by two methods. The formation of thin films by electrodeposition of polypyrrole doped with polyanions able to complex silver ions, and their characterisation by SEM, FTIR and microbiological testing is described. The alternative method, involving chemical grafting of a thin film of a quatemaiy ammonium polymer using a surface initiator, is also discussed. 2 refs. 

The tests of additives in spirally wound VRLA batteries [18] also included a proprietary AD7 additive, which was chemically described as polyvinylsulfonic acid or its salts, called polyvinylsulfonates [85,86], together with crystal carbon fibres, polyester fibres and Sn02 powder. None of the additives were found to increase the initial discharge capacities compared with the control. The AD7 additive did, however, show significantly better maintenance of capacity during cycling than the control. It was further claimed [81,82] that typical additive concentrations of about... 

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