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Graphite Coated with Glassy Carbon

 

We offer graphite coated with glassy carbon, or both impregnated and coated with glassy carbon. The glassy carbon coating completely seals all exposed surfaces, while the impregnation seals and penetrates the substrate to more than 0.25.


Benefits of Glassy Carbon Coating
  • Stops out gassing problems
  • Stops absorption of contaminants into the graphite porosity
  • Dramatically reduces particulate generation common to graphite materials
  • Gives a uniform and continuous carbon surface that enhances the electrical and thermal uniformity of the graphite substrate
  • Withstands fluorine based etch systems significantly better than SiC coatings



Glassy Carbon Coating Solves Problems
Typically Associated with Graphite

The macro structure of graphite is very much like a sponge. About 20% of the graphite's volume consists of pores and inclusions. Because of the small sizes of the pores and inclusions for the given pore volume, graphite actually has a much larger surface area than that dictated by the geometric surface area of a given part. This allows the graphite to absorb gases and liquids to a greater extent than continuous solid materials. The porous nature of graphite will cause problems in processes that require tight control of the chemical environment. Gases or liquids absorbed in previous uses of the graphite artifact will out gas over a long period of time and pollute the critical process environment. The glassy carbon coating stops absorption and out gassing by sealing off the porosity with a uniform, continuous carbon coating, thus preventing process complications due to contamination being introduced from the porosity of the graphite.

Being a porous material, the density of the graphite varies from vicinity to vicinity with respect to variations in pore sizes and quantity of pores in a given volume. Changes in density affect the electrical and thermal conductivity in the associated region. In cases where graphite is being used as electrodes, variations in density will cause variations in the electric field. If the electric field is critical in depositing a film or layer during the process, the thickness uniformity of the deposited layer will be adversely affected. In a similar manner, if the product being processed requires uniform heating from the graphite artifact while in contact with it, optimum process conditions may not be practical due to variations in thermal conductivity of the graphite surface. When the glassy carbon coating is applied, a uniform density is obtained in the surface region of the graphite. This result significantly improves the uniformity of an electric field being generated and/or of heat being transferred conductively to the product being processed. If the process being considered involves the deposition of a film, this means that a more uniform film thickness can be obtained.

Because grains of graphite have a structure similar to that of mica, graphite particles are easily rubbed off. This results in unwanted graphite particles floating around during a process and possibly contaminating the product being processed. The glassy carbon coating has an amorphous molecular structure similar to glass. This type of structure does not readily particulate. By coating the graphite with the glassy carbon coating, the graphite grains are held in place by the coating and are no longer able to easily rub off the surface, thus creating a processing environment free of graphite particles.

Graphite and carbon materials exhibit extraordinary chemical inertness to over 2,800 C. The exception to this is heating graphite to above 400 C in the presence of oxygen, water, or other oxygen containing reactants. Typically coatings on graphite containing silicon, titanium or other non-carbon components are more reactive to the process chemicals than the graphite itself. Because the glassy carbon coating is composed only of carbon, it maintains the same chemical inertness as the graphite substrate. This reduces complications caused by side reactions with other coating materials.