I'm in the process of designing thermal evaporation chamber for experimental purposes. The temperatures in the chamber will easily exceed 600C which means that any sealing solution must either (A) Be placed in area that is far enough from the heat source to withstand the extreme heat or (B) Simply be made of a material that can withstand the high temperatures experienced in the chamber. O-Rings constructed of Viton are by far the most common for applications like this, but have to be designed carefully. As such, I'm considering the use of gaskets constructed of flexible graphite or "Graph foil". These seem like they might work but I am unsure if their sealing proprieties are sufficient for a vacuum chamber, can anyone fill me in?
Flexible graphite is an excellent sealing material in 250-700C temperature range. There are some care needs to be considered before putting them.
They are difficult to machine at they are fragile and may break at some areas where material is not enough. So you need to put enough thickness around the holes and edges.
They are not reusable due to high plasticity as their structure changes after first compression.
Generally they need to be compressed to 50% to provide adequate sealing. Thickness should be sufficient enough to start with and it should be tested before finalizing on the machining tolerance of mating parts.
They do absorb high amount of IR radiation so direct exposure should be avoided.
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