Carbon films are thin film coatings, which consist predominantly of the chemical element carbon. They include plasma polymer films, amorphous carbon films, CVD diamond films as well as graphite films. Carbon films are produced by deposition using gas-phase deposition processes in most cases taking place in a vacuum. They are deposited in the form of thin films with film thicknesses of just a few micrometres. Carbon films make it possible to implement a large number of surface functions, especially in applications where wear is a major factor.
Carbon foils are stocked in five basic forms:
Pyrolytic graphite – It is a strongly anisotropic, high density, high purity material manufactured by Chemical Vapour Deposition (CVD). It is non-porous and self-lubricating, lightweight and shows excellent thermal shock resistance. It can be easily machined with normal metalworking tools.
Flexible graphite – It is an exfoliated material that is mechanically bonded to form thin, flexible sheet. It is commonly used as a gasket material for corrosive or high temperature service.
Rigid graphite sheet – It is a rigid form of graphite. The exceptional corrosion resistance and high temperature properties of graphite make this material suitable for applications as diverse as heat exchanger blocks for chemical process plant and arc furnace electrodes used in steel manufacture.
Highly Oriented Pyrolytic Graphite (HOPG) – A highly oriented form of high purity pyrolytic graphite, which diffracts x-rays and neutrons with greater efficiency than any other material.
Vitreous or Glassy Carbon – This material has high flexural strength with zero open porosity and, hence, a low permeability to gases.
Carbon in the format of a foil, especially ultra-thin foils, has found application in space instruments. Suspended on fine metallic grids, these foils have proved to be robust in surviving the rigors of launch and space environments, and have served over long mission lifetimes.