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Carbon Fiber:
The first carbon fibre for commercial use was fabricated by Thomas Edison.
- Sixth lightest element and carbon - carbon covalent bond is the strongest in nature.
- Edison made carbon fiber from bamboo fibers.
- Bamboo fiber is made up of cellulose.
- Precursor fiber is carbonized rather than melting.
- Filaments are made by controlled pyrolysis (chemical deposition by heat) of a precursor material in fiber form by heat treatment at temperature of 1000-3000
- The carbon content in carbon fibers is about 80-90 % and in Graphite fibers the carbon content is in excess of 99%. Carbon fibre is produced at about 1300 while the graphite fibre is produced in excess of 1900 .
- The carbon fibers become graphitized by heat treatment at temperature above 1800 .
- “Carbon fibers” term is used for both carbon fibers and graphite fibers.
- Different fibers have different morphology, origin, size and shape.
- The size of individual filament ranges from 3 to 147 .
- Maximum use of temperature of the fibers ranges from 250 to 2000 .
- The use temperature of a composite is controlled by the use temperature of the matrix.
- Precursor materials: There are two types of precursor materials (i) Polyacrylonitrile (PAN) and (ii) rayon pitch, that is, the residue of petroleum refining.
- Fiber properties vary with varying temperature.
- Fiber diameter ranges from 4 to10 .
- A tow consists of about 3000 to 30000 filaments.
- Small diameter results in very flexible fiber and can actually be tied in to a knot without breaking the fiber.
- Modulus and strength is controlled by the process. The procedure involves the thermal decomposition of the organic precursor under well controlled conditions of temperature and stress.
- Cross section of fiber is non-circular, in general, it is kidney bean shape.
- Heterogeneous microstructure consisting of numerous lamellar ribbons.
- Morphology is very dependent on the manufacturing process.
- PAN based carbon fibers typically have an onion skin appearance with the basal planes in more or less circular arcs, whereas the morphology of pitch-based fiber is such that the basal planes lie along radial planes. Thus, carbon fibers are anisotropic.
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