Our graphite materials can be purified to less than 5 ppm, densified to reduce open porosity by as much as 80%, or impregnated with resins, oxidation inhibitors, or metals. Surface treatments and coatings are available that provide a sealed surface to improve wear characteristics or to reduce particles.
Our unpurified graphites have typical impurity levels over 3,000 ppm. Metals are the major constituents, and our purification process reduces impurities to 5 ppm (99.9995%) or less as determined by ash analysis."
The process of manufacturing bulk synthetic graphite yields tiny voids (pores) that may link to the surface (open porosity) or be isolated (closed porosity). Densification partially fills the open pores with pure carbon, reducing the average pore size and open porosity. The open porosity is reduced by 80% through the process, resulting in graphite with higher density and reduced permeability.
Graphite is subject to oxidation at high temperatures, typically above 450°C. The oxidation threshold of our graphite grades may be increased an additional 50°C through purification, which removes catalysts that accelerate the oxidation process. Service temperature can be raised further, to 600°C, by impregnating the pore structure of the graphite with a phosphate glass.
Resin impregnation completely blocks the pore structure. This is applied to keep fluids or gases from penetrating the graphite pore structure. The CFS process must be applied to bulk materials with a maximum cross section of 0.6". The maximum service temperature for the CFS impregnated material is approximately 150°C.
An acrylic impregnation keeps fluids and gases from penetrating the pore structure of the graphite and prevents cross talk between pores, much like the CFS impregnation. This process, however, yields a less abrasive material, increasing machinability and reducing the total cost of finished components. The process may be applied to bulk materials with a maximum cross section of 1". The recommended maximum service temperature for the impregnated material is approximately 150°C, with short-term excursions up to 200°C.
Nickel metal is impregnated into the porosity of the graphite to adjust its acoustic characteristics for use in non-destructive testing applications. The combination of our unique microstructure and the nickel impregnation gives an ultrasonic velocity and impedance that meets the requirements of multiple applications.
Silicon Carbide Coating
Silicon carbide (SiC) can be applied to graphite or solid SiC substrates. The coating is 75 microns thick and seals the underlying porosity. The SiC coating is applied via chemical vapor deposition and is inert to high temperature, acid attack, and chemical erosion that will degrade graphite and other ceramics.
Pyrolitic Carbon Treatment
Parts go through a unique, proprietary CVI process that provides a nonporous surface with an amorphous carbon coating. The treatment completely seals the surface of 1 and 5 micron grade graphites and reduces particle generation in cleanroom or other highly defect intolerant environments. The treatment must be performed on finished components.