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Carbon-Carbon Composites

Structure of Carbon-Carbon Composites

Carbon-Carbon (C/C) Composites may be manufactured with different orientation of the reinforcing phase (carbon fibers): unidirectional structure, bi-directional structure (cloth made of multiple carbon fiber yarns), multi-directional structure (3D, 4D, 5D, etc.).
Multi-directional reinforcement provides maximum level of mechanical properties in the directions of the woven structure.
The simplest multi-directional reinforcement consists of 3D orthogonal structure woven of straight carbon fiber yarns.

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Fabrication of Carbon-Carbon Composites by Liquid Phase Infiltration process

  • Preparation of carbon/Graphite fiber preform of the desired structure and shape.
  • Infiltration of the preform with a liquid precursor: petroleum pitch/phenolic resin/coal tar.
  • Pyrolysis/carbonization (chemical decomposition by heat in the absence of Oxygen) of the polymer precursor at 1000-1830ºF (538-1000ºC) under normal or high pressure.
  • Infiltration – pyrolysis cycle is repeated several (3-10) times until the desired density is achieved.
  • Graphitization heat treatment. At this stage amorphous carbon is transformed into crystalline graphite. The temperature of the treatment may vary within the range 2700-5400°F (1500-3000°C). Typical graphitization temperature is 4530°F (2500°C). Graphitization of carbon-carbon composites results in increase of Modulus of Elasticity and strength of the composite.

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Fabrication of Carbon-Carbon Composites by Chemical Vapor Deposition process

  • Preparation of carbon/Graphite fiber preform of the desired structure and shape.
  • Densification of the composite by Chemical Vapor Deposition (CVD) technique. The CVD process involves infiltration of the preform with a pressurized hydrocarbon gas (propane, methane, propylene, acetylene, benzene) at 1800-2200ºF (982-1204ºC). The gas is pyrolyzed forming carbon deposition on the fiber surface. The process duration is determined by the thickness of the preform, through which the gas diffuses.
  • Graphitization heat treatment. At this stage amorphous carbon is transformed into crystalline graphite. The temperature of the treatment may vary within the range 2700-5400°F (1500-3000°C). Typical graphitization temperature is 4530°F (2500°C). Graphitization of carbon-carbon composites results in increase of Modulus of Elasticity and strength of the composite.

Fabrication of Carbon-Carbon Composites by Chemical Vapor Deposition process results in higher (as compared to Liquid Phase Infiltration technique) Modulus of Elasticity and mechanical strength.

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Properties of Carbon-Carbon Composites

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Oxidation protection of Carbon-Carbon Composites

The main disadvantage of Carbon-Carbon Composites is their low oxidation resistance. Carbon materials react with Oxygen at temperatures above 900ºF (482ºC).

The following methods are used for oxidation protection of Carbon-Carbon Composites:

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Applications of Carbon-Carbon Composites

  • High performance braking systems (eg. brake discs for high speed aircrafts);
  • Refractory material (eg. protection tubes and grids);
  • Hot-pressed dies;
  • Heating elements;
  • Turbojet engine components (eg. rocket nozzles).

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carbon-carbon_composites.txt · Last modified: 2012/06/02 by dmitri_kopeliovich
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