Decaborane handling and the vacuum system

[Rezwan]

From the email exchange:

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.

[belbear]

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.

[Author]

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