[labnetwork] Does anyone use forming gas in vacuum systems

[Bob Hamilton]

Bruce Tolleson,

You'll have no issues with 5% H2 in N2 in a vacuum chamber. H2 in air 
has a lower flammable limit (LFL) of 4.7. The lower explosive limit is 
more like ~19% in air under ideal conditions. Given a starting point o 
5% H2 in pure N2 the LFL will be higher.

To adjust this for reality I'll share my experiences. I routinely used 
20% H2 in N2 to seal vacuum tubes with an open flame and never saw 
combustion. Ditto for 10%. These mixes were used for decades before me 
in UC Tube Laboratory before I joined that group so there is a long 
history of safety. Hi-vacuum brazing was routinely done under vacuum 
with forming gas added as a reducing agent (and often pure H2).

Regards,
Bob Hamilton

On 5/1/2014 7:39 AM, Bruce Tolleson wrote:
>
> Dear Labnetwork,
>
>   I have a project that requires forming gas (5% hydrogen, 95% 
> Nitrogen) for gettering to reflow metal in a vacuum chamber. Has 
> anyone done forming gas in a vacuum system and what precautions are 
> required for the pumping system?
>
> Bruce E. Tolleson
>
> Rochester Institute of Technology
>
> 82  Lomb Memorial Drive, Bldg 17-2627
>
> Rochester, NY 14623-5604
>
> (585) 478-3836
>
> http://www.rit.edu/~962www/logos/tiger_walking_rit_color.jpg
>
>
>
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-- 
Robert Hamilton
University of California at Berkeley
Marvell NanoLab
Equipment Eng. Mgr.
Room 520 Sutardja Dai Hall
Berkeley, CA 94720-1754
bob at eecs.berkeley.edu
Phone: 510-809-8600
Mobile: 510-325-7557 (Emergencies only)
e-mail preferred

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