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First carbon fibers are made by pyrolizing Poly-acrylo-nitrile (PAN) fibers

Pyrolized fibers then woven into the desired pattern

Spaces between the fibers are filled by Chemical

Vapor Deposition (CVD) &Infiltration process

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Liquid Phase Infiltration processChemical Vapor Deposition process

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Graphitization heat treatment. At this stage amorphous carbon istransformed into crystalline graphite. The temperature of the treatment

may vary within the range 2700-5400F (1500-3000C). Typicalgraphitization temperature is 4530F (2500C). Graphitization of carbon-

carbon composites results in increase ofModulus ofElasticity andstrength of the composite.

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http://www.substech.com/dokuwiki/doku.php?id=tensile_test_and_stress-strain_diagramhttp://www.substech.com/dokuwiki/doku.php?id=tensile_test_and_stress-strain_diagramhttp://www.substech.com/dokuwiki/doku.php?id=tensile_test_and_stress-strain_diagramhttp://www.substech.com/dokuwiki/doku.php?id=carbon-carbon_compositeshttp://www.substech.com/dokuwiki/doku.php?id=carbon-carbon_compositeshttp://www.substech.com/dokuwiki/doku.php?id=tensile_test_and_stress-strain_diagramhttp://www.substech.com/dokuwiki/doku.php?id=tensile_test_and_stress-strain_diagramhttp://www.substech.com/dokuwiki/doku.php?id=graphite_manufacturing_process

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The invention relates to find the field of hightemperature composites made by the chemicalvapoure infilteration and deposition of a bondingmatrix within a porous structure.

More perticularly the invention relates to highpressure gradient processes for forcing a infiltrationof reactant gas in to a porous structure.

Chemical vapoure infilteration and deposition is awell known process for depositing binding matrixwithin in a porous structure.

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The technique particularly suitable for fabricating high

temperature structural composites by depositing ceramicmatrix within a ceramic porous structure resulting in a

very use full structure such as carbon/carbon AIR

BRAKE DISC AND TURBINE COMPONENTS.

The generally CVD/CVI process are classified 4 types

1.Isothermal process

2. thermal gradient process

3. pressure gradient process

4. pulsed flow process

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in a pressure gradient CVI/CVD process, A fibre

preform is placed in a gas tight unit and heated.

the reactant gas is forced to flow through the porous

structure by inducing a pressure gradient from one

surface of the porous structure to an opposing

surface of porous structure.

The flow rate of reactant gas is greatly increasedrelative to the iso-thermal and thermal gradient

process which results in increased deposition rate of

the binding matrix.

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This process also known as forced-flow CVI/CVD.

Pressure gradient CVI/CVD tend to become complex,

expensive and difficult to implement for densifyinglarge quantities of porous structure.

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These are the plastics which can be reheated andreformed into new shapes for an number of timeswithout significant change in their properties .

Thermoplastics consists of very long main chain ofcarbon atoms which are covalently bonded together.

Plastic materials have relatively low density.

The tensile strength of the plastics are relatively low.

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Thermosetting plastics will be formed into permanentshapes and set by a chemical reaction .

It cannot be remelted and reformed into desired shape

once it set.

When it is heated to high temperature it willdecomposes or degrade so thermosetting plastics

cannot be recycled or re worked.

Ex: phenolics, epoxies, melanine, bakelite etc

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It is a thermo-chemical decomposition of organic

material at elevated temperatures without the

participation of oxygen.

It involves the simultaneous change of chemicalcomposition and physical phase and is irreversible.

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Here laminated structure is pyrolysed in an inertatmosphere to around 1000 C.

the resulting product is heated to 2500 C to bring about

graphitisation of carbon matrix this is an extremely in

efficient process nevertheless.

It is inexpensive and quick and imposes no size

limitation

The techniques such as hand lay-up, pultrusion, prepegging, filament winding or compression molding may

be used to obtain the laminating structure.

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Hot iso-static pressure impregnation carburization often

referred to as a HIPIC process is used to form C-Ccomposites it involves the following steps.

1. A dry fibre preforms or porous laminate is vaccume

impregnated with molten pitch.

2. It is placed in a metal can or container and surrounded by aexcess pitch.

3. The can is evacuated and sealed .

4. It is then placed in a HIP unit .

5. Temperature is raised above the melting point of pitch

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6 . Pressure is increased to 100 Mpa ,pitch melts,

expands and is forced into the pores in the sample.

7. The sealed container acts like a rubber container and

helps in carrying the pitch to the interior portion of

the sample through the pores.

8.Carbonisation takes place, the pressure applied

increases the yield of carbon from pitch.7. After processing, the preform is removed from the

container and it is cleaned.

8. It is graphitized by heating to 2300 C.

the above step is repeated till the required density is

obtained

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