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Home \ CVI/CVD CHEMICAL REACTORS


CVI/CVD CHEMICAL REACTORS

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CVI/CVD CHEMICAL REACTORS

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CVI/CVD CHEMICAL REACTORS

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GENERAL INFORMATION

A CVI/CVD chemical reactor is a complex plant that fabricates composite materials with non-oxidic continuous or short fibers (CC, SiC or C/SiC) starting from carbon fiber, alumina or silicon carbide preformed materials. The best quality products are generated by the Chemical Infiltration Process from vapour phase (Chemical Vapour Infiltration). This process may occur in a chemical reactor that works at constant temperature and pressure (CVI Isobaric and Isothermal). With this process a final density in the order of 90% of the theoretical density on thicknesses of about 10 mm may be reached.

The process implies a flow of reacting gases (Methyltrichlorosilane + H2 for Silicon Carbide and CH4 and Ar for pyrocarbon) inside a reacting chamber, whose walls are chemically inert, at velocity and pressure such that they can enter into the porous materials creating solid plugs in the porosities of the original ceramic preformed materials until the required density is reached.

Main characteristics of these materials are:

  • They are extremely resistant to high temperatures ( 3000C in the case of C/C in neutral or reducing atmosphere and 1700 C in a oxidizing atmosphere
  • They show a pseudo-ductile behaviour even if they are ceramic materials
  • They are extremely light (the weight/ultimate tensile strength ratio is very low)

These composite materials based on a ceramic matrix are very useful in aerospace and aeronautic applications and, more recently, also in high performance car brakes.

 

CHARACTERISTICS

The chemical reactor is a plant with the following main parts:

  • The vacuum furnace
  • The Power supply system
  • The control panel
  • The gas management service module
  • The pumping station
  • The purifiers

The dimensions and detailed chracteristics depend on the working volume in the furnace and on the required process conditions.

 

GENERAL TECHNICAL SPECIFICATIONS

- Working volume:

according to the need

- Loading:

upper or lower loading

- T:

1600C

- Resistor:

Graphite

- Thermal insulation:

dense graphite fibers

- Electrical power:

it depends on the working volume

- Max Temperature ramp up:

600C/h

- Vacuum chamber:

Duplex steel (SAF 2205 or 2507) cold walls with external cooling. Remote control of the opening and lifting of the cover

- Control system:

automatic control of the entire cycle by PLC

- Gas supply:

CH4, N2, MTS (Methyltrichlorosilane), H2 and Ar, supply controlled by a Mass Flow Controller (MFC)

- Vacuum pumps:

combination of two pumps in series; a dry preliminary pump (anti-corrosion version) and a roots pumps of the needed characteristics

- Filters and purifiers:

High efficiency particle filters (HEPA) upstream the vacuum pump system and a scrubber in counterflow and sodium hydroxide recirculation at 20% for gas purification before release into the atmosphere

- Safety and alarms:

there are a series of safety features and alarms to assure a safe operation with equipment complying with ATEX regulation

- Codes and standards:

the plant is designed according to European standards and is features a CE marking

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

SPECIAL DESIGNS

In order to drastically reduce the process time and to increase the thickness of the preformed materials (up to 20-30 mm) the chemical reactors CVD/CVI can be supplied as special design featuring a thermal gradient in the material thickness (TG-CVI thermalgradient CVI)

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TYPICAL DISPOSITION FOR CVI/CVD CHEMICAL REACTOR