Amorphous carbon fibres

The commercial appearance of phenolic resins fibres in 1969 is, at first consideration, one of the more unlikelier developments in polymer technology. By their very nature the phenolic resins are amorphous whilst the capability of crystallisation is commonly taken as a prerequisite of an organic polymer. Crystallisability is not, however, essential with all fibres. Glass fibre, carbon fibre and even polyacrylonitrile fibres do not show conventional crystallinity. Strength is obtained via other mechanisms. In the case of phenolic resins it is obtained by cross-linking. 

Generalized results of the analysis made by different methods show that obtained CNM are filament nanocarbon fibres (CNM) with diameter from 8 to 100 nm, consisting of the polycrystalline nanographite entrained in amorphous carbon (Fig. 5). 

El4.21 Glasses are amorphous silicon-oxygen compounds. Starting from sand (which is mostly pure SiOi) and other oxide additives, a wide variety of glasses with different properties can be obtained, used and seen every day. Activated carbon (used as adsorbent), carbon fibres (used as additives in plastic to increase the strength), and carbon black (used as pigment) are three examples of amorphous and partially crystalline carbon. 

The production process of activated carbon fibre consists of the development of amorphous carbon flbres at around 1000°C from fibre precursors, followed by physical activation either by steam at 800-1000°C or chemical activation. The organic fibre precursors include polyvinylidene chloride (PVDC) fibres (Saran), phenolic fibres (Kynol) , poly (acrylamide), polyacrylonitrile (PAN) and rayon fibres activated carbon fibres can also be made from vapour-grown fibres, nanotubes and... 

WAXS measurements are based on the ratio of the intensity of the crystalline peaks and the amorphous background. Fitting the amorphous background is best done with the help of a computer. Various corrections can be applied to obtain more accurate absolute crystallinities. However, most frequently we are interested in approximate absolute but accurate relative crystallinities and the corrections are not always necessary. The peak width can give information on crystal perfection - sharper peaks indicate more perfect crystals. Two-dimensional diffraction patterns of isotropic materials show rings corresponding to the diffraction peaks. Intensity variations within the rings can be used to assess crystalline orientation. WAXS only looks at material which can be penetrated by X-rays and so the depth of the analysis is limited. The patterns for filled systems can be hard to interpret but various methods have been developed - for example for use in continuous carbon-fibre composites. 

PAS is an amorphous resin produced by Phillips Petroleum. PPS and PEEK are polyphenylene sulphide produced by Phillips Petroleum and a semi-crystalline polyether ether ketone from ICI, respectively. PEEK is combined at source with a carbon fibre reinforcement to give APC2. Reinforcements are T650-42 carbon fibre, manufactured by Amoco, and AS4 and IM6 carbon fibres made by Hercules. 

Comments Tg = 143 C, Density of amorphous material = 1.26 g/cm", GF = Glass fibres, CF = Carbon fibres, SG = Speciality grade, PF = Fine powder for coatings and compression moulding. ... 

The reinforcing filler usually takes the form of fibres but particles (for example glass spheres) are also used. A wide range of amorphous and crystalline materials can be used as reinforcing fibres. These include glass, carbon, boron, and silica. In recent years, fibres have been produced from synthetic polymers-for example, Kevlar fibres (from aromatic polyamides) and PET fibres. The stress-strain behaviour of some typical fibres is shown in Fig. 3.2. 

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