Coatings for high density graphite machined components & assemblies

As discussed in our graphite pages, there are three main problems that can be experienced when using high density or high strength graphite in semiconductor or vacuum production environments. These are particle contamination, oxidation and excessive outgasing. All of these problems can be eliminated by coating the graphite component after machining. We can coat machined graphite components with a range of materials to suit various applications and different graphite base grades. 

The coatings available are:

• Pyrolytic Graphite- impervious coating with similar chemical properties to graphite.
• Silicon Carbide-impervious coating, non electrically conductive and can be used up to 1500°C in air.
• Pyrolytic Boron Nitride-impervious coating, excellent chemical resistance, excellent electrical insulator, suitable for 900°C in air & 2000°C in vacuum.
• Aluminum Nitride- non conducting, good ware resistance and used to 1000°C in air

We are always looking to develop our range of coatings and surface treatments. If you have a requirement for a special material to be coated on to a graphite component we would be happy to look at the feasibility of achieving it. Previous projects have included coating graphite with Aluminum Nitride and another with Titanium Nitride.

Surface Treatments for High Density Graphite
If outgasing is not a problem and low particle contamination is required, we can offer the following surface treatments :

• Vitreous Carbon Impregnation- does not alter the graphite's physical properties but substantially reduces particle contamination.

• Pyrolytic Graphite Impregnation- PG impregnates up to 5mm into the graphite's surface, forming a dense virtually impermeable layer. A thin coating is also formed on the surface. This is suitable for high wear applications, such as implanter electrodes, greatly reducing wear and particle emissions and substantially increasing component life.

• Silicon Carbide Conversion- The top 3-4mm of the graphite's surface are converted to Silicon Carbide. This forms a hard, electrically conductive but particle free layer. This layer has an open porosity of approximately 12%, which means the graphite core can still be oxidized or attacked chemically, leaving a hollow component.

• Total Silicon Carbide Conversion- It is possible to totally convert a graphite component to Silicon Carbide, providing the maximum thickness of any section is not greater than 7mm.It is possible to bond graphite sections together, before conversion, to form a component such as a vertical wafer carrier. As this material is totally converted and contains no free graphite, and is electrically conductive. It is ideal material for producing heating elements that are used in an oxygen environment.

If you have an application or a prototype component, we would like to develop or recommend a surface treatment that will increase its application life. Please contact us using this form with your details. Our quality, technical knowledge and fast turn around on coated components make us a leader in this industry.