Carbon fibers for carbon-carbon applications (4)

Carbon-carbon for aircraft: an aircraft capable of reaching Mach Ⅱ requires a high performance turbojet engine and carbon-carbon with high temperature and load bearing capability has been used successfully for making a turbine wheel capable of operating at 40,000 rpm. To confer extra strength, an extra impregnation/pyrolysis cycly was introduced. The bond between fibers and matrix must not be too strong, which would result in brittleness and at the same time, must not be too weak, which would allow the fibers to debond. In a 2D lay-up, the principal mode of failure is due to interlaminar shear, failing by delamination between the plies. The strength parallel to the fiber is some 15 times greater than in the transverse direction, hence if failure is expected transversely, a 3D structure might be preferred.

Carbon-carbon has also been used for ice protection on aircraft.

Rocket motor nozzles and expansion tubes: For rocket motor nozzles and expansion tubes, FMI utilizes a 3D woven carbon cloth, after examining the weave integrity by using X-rays. The woven structure is pressure impregnated with molten pitch to fill all the interstices, followed by densification and pyrolyzation. Carbon-carbon will endure flame temperatures up to 3,300C.

SEP uses a carbon/SiC composite for liquid rocket engine nozzles which can withstand an operating temperature of 1975C and 2275C for a few seconds.

Carbon-carbon in engines:

  1. Bearings and seal—carbon-carbon has good wear, friction and thermal characteristics.
  2. Valve guides—carbon-carbon has a low coefficient of friction, typically 0.1, over a wide temperature range and it is hoped that current research will negate the use of the engine oil lubricant, which could improve engine power. A near-frictionless grade of carbon-carbon has been developed, offering uniform frictional characteristics in the temperature range 25-800C, and is associated with extremely good wear resistance.
  3. Pistons—conventional Al pistons have a density of 2.7g/cm3, but carbon-carbon, with a density of 1.75g/cm3, offers a significant weight saving, which can be translated into engine power. In addition, the carbon-carbon offers good strength retention at elevated temperatures, permitting the design of piston to have a better fit, giving a reduction in unburned fuel and providing a greener environment. The low coefficient of thermal expansion suggests that a carbon-carbon piston could be used with a carbon-carbon liner to produce a ringless piston.

Carbon-carbon for biomedical end uses: carbon-carbon has good compatibility with living tissue as well as chemical inertness and has been used for implants.

Carbon-carbon in industry: Carbon has been used in the chemical industry as a material for construction, offering very good corrosion resistance but, unfortunately, it is mechanically weak and is readily broken—a situation that can be solved by replacing with carbon-carbon, which has the chemical resistance of graphite combined with the mechanical strength of metals. It can be used for column packings in distillation columns, distillation trays and supports, sparger tubes, feed pipes, mist eliminators, thermowells and pump impellers. The product is resistant to a wide range of chemicals including HF, HCL, HBr, H2S, H2SO4, H3SO4 and NaOH.

Carbon-carbon is also used for furnace heating elements, hot gas ducts, hot press dies, molds, items for handling hot glass in the glass making industry and mechanical fasteners including bolts, nuts and studs.

 

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