Decaborane and the Vacuum System
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Discuss In ForumsMurali and Alex discuss the effects of decaborane on the vacuum system.
Hi Alex,
Another question - what do we need to do to protect our vacuum system (roughting pump and turbomolecular pump)?
I am planning to use a heated oil bath and then circulate the oil all around the chamber by using metal tubes welded to the chamber. We also intend to run the exhaust of the vacuum through water, but am worried that this may cause back up pressure problem, should we use a second roughing pump behind the first?
Thanks,
Murali
The oil bath with circulation is a good idea. It’s similar to something I did a few years ago.
I don’t remember the pumps having problems with the decaborane. But it might affect pressure readings from ion gauges. We always had scrubbers in the exhaust so did not worry about this aspect of operation. I think you are right, that you will have a back up pressure problem if you pump the decaborane through water. The chamber will have a high level of water. I think you should look into a gas scrubber. See http://www.spectragases.com/content/gasscrubbers.htm
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Science rul3z!
My idea is that you can diminish contamination from boron compounds to critical parts like electrodes, coils, observation windows and vacuum pump by creating a refrigerated “cold trap” inside your vacuum chamber. Also the outlet toward the vacuum pump can be cooled to trap the boron before it enters the pump.
Essentially, the coldest surface around will draw most of the excess borane toward itself, keeping everything else much cleaner. And if that cold trap is a smooth surface, it can be cleaned much easier than all those complex components.
You can add some coolant piping around part of the vacuum vessel, using part of the vessel wall as a cold trap. Or place a dedicated cold trap heat exchanger inside the vessel.
Essentially, it needs to be nothing more than a copper plate with some thin copper piping soldered to it, through which the coolant flows.
Hi Murali,
Put heater blankets on all parts of your system you do not wish condensation. Check the specs on the turbo pumps, you can heat the pumps (heater blankets) to prevent condensation. Also heat your window so it does not coat up. Choose one piece of your system to condense the extra decaborane. Then you just need to clean just that piece. Do scrub the ouput of your pumps. Contact someplace like Kurt Lesker for supplies and guidance. Thre is nothing particularly unique about what you are trying to do. it is common in the industry.
Richard
Here is a link for heated windows.
http://www.thermionics.com/Legacy/Chambers/vhw.aspx
You can find everything you need via google.
A heated maglev turbo pump can handle this without buildup. Use dy pumps so you don’t have to deal with toxic oil and byproducts. let the scrubber handle the resulting toxics.
Do it right and it will be quite safe. A plasma clean (O2 or N2) will be good to perform prior to opening the system.
Richard
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