Application of Carbon fibers in metal matrices

Electromagnetic interference and heat dissipation: the problem of electromagnetic interference and dissipation of heat emitted from electronic products such as computers has become a challenge and EMI is said to exist whenever undesirable voltages or currents are present, adversely influencing the performance of a device. The problem can be alleviated either by making the insulative plastic conductive or by incorporating a metal coating to the surface of the plastic. The plastic may be made conductive by incorporating carbon fiber or a metal coated carbon fiber in a thermoplastic molding compound.

  1. Carbon fiber as the conductive material—high carbon fiber content will provide 40 dB of shielding in the 30 MHz-1 GHz range.
  2. Metal coated carbon fiber as the conductive material—metal coated carbon fiber has been used for providing lightening strike protection, EMI/RFI shielding and static dissipation. End uses include Green chaff, Stealth applications, de-icing and power grid counter measures. Composite Materials, LLC has introduced Compmat MCG, a 99.9% pure Ni coated graphite fiber, available in continuous, chopped, mat or tap forms. The chopped form can be supplied with a variety of sizings to optimize dispersion in each type of molding resin.
    1. Plated carbon fiber—electroplated or electroless plated deposits are not pure and are limited to the thickness that can be applied.
    2. INCO Ni coated carbon fiber—INCO have developed a method of coating carbon fiber with Ni using an adaptation of the carbonyl process by the thermal decomposition of nickel carbonyl gas:

Ni(CO4) ⇋ Ni + 4CO ↑

Deposits of 99.87% Ni can be coated on unsized carbon fiber to give products with 20-55% w/w No. For electronic applications, to obtain an optimized target level of 42-48%, thermoplastic compatible size can be applied to the Ni coated carbon fiber, which has been chopped to 6mm length and the chopped product incorporated in a thermoplastic matrix to give a concentrate. This composite contains 60% Ni, which can be dry blended with a compatible thermoplastic molding compound and finally injection molded to provide EMI shielding for thermoplastic parts. Using this technique, longer carbon fiber reinforcement can be utilized, giving more effective utilization.

Maximum shielding attenuation is achieved with about 15% Ni coated carbon fiber.

Nickel coated carbon fiber can be used as a conductive plate for fuel cell plates, ice trays and automotive mirror housings; an electronic housing to provide EMI shielding for computers, cellular phones, anti-lock brakes, coaxial cable and telecommunication; as EMI shielding at electronic board level for computers, cellular phones and 900 MHz phones. Bell and Hansen have described the use of Ni coated fibers for aerospace applications.

Other end uses for carbon fibers: Chung and Wang have investigated the concept of opto-electronic and electronic devices made from carbon fiber polymer matrix structural composite and as capacitors.

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