Helium infiltration, NOS Valves - Page 2 - UK Vintage Radio Repair and Restoration Discussion Forum

Philips210 · 4th Oct 2017, 3:28 pm

Hi.

Out of curiousity, could the problem actually be worse if the valves were exposed to a significant amount of hydrogen?

Regards
Symon.

dave cox · 4th Oct 2017, 3:57 pm

Possibly, hydrogen will get locked into the lattice and not penetrate. This certainly happens with metals, then known as interstitial-hydrides.

dc

kalee20 · 4th Oct 2017, 10:44 pm

Good point.

Helium is a pain because each atom is light, so at a particular temperature must move very fast, thus has a good chance of penetrating anything in its way. And being inert, don't get locked into combination with anything.

Hydrogen molecules are lighter still, so move even faster - but can be caught by anything that fancies bonding chemically with them.

dominicbeesley · 6th Oct 2017, 11:22 am

I'm guessing also that because they're inert the getter doesn't, well, get em!?

kalee20 · 6th Oct 2017, 1:20 pm

It doesn't. Nothing combines with helium. Not even fluorine, which can be enticed to combine with xenon and krypton (and presumably radon).

Luckily, proportion of atmospheric helium is very low.

I do recall a manufacturer of light bulbs, making a range with super-thick glass envelopes, for use inside divers' decompression chambers. Otherwise helium diffused in, the filament was cooled more and more, and efficiency dropped.

dave cox · 10th Oct 2017, 2:01 pm

Hydrogen has an impressive diffusion speed at RTP (room temperature and pressure). Well above the speed of sound if I recall correctly !

dc

4th Oct 2017, 3:28 pm	#21
Philips210 Nonode Join Date: May 2007 Location: Redruth, Cornwall, UK. Posts: 2,573	Re: Helium infiltration, NOS Valves Hi. Out of curiousity, could the problem actually be worse if the valves were exposed to a significant amount of hydrogen? Regards Symon.

4th Oct 2017, 3:57 pm	#22
dave cox Nonode Join Date: Jan 2009 Location: Bristol, UK. Posts: 2,062	Re: Helium infiltration, NOS Valves Possibly, hydrogen will get locked into the lattice and not penetrate. This certainly happens with metals, then known as interstitial-hydrides. dc

4th Oct 2017, 10:44 pm	#23
kalee20 Dekatron Join Date: Feb 2007 Location: Lynton, N. Devon, UK. Posts: 7,081	Re: Helium infiltration, NOS Valves Good point. Helium is a pain because each atom is light, so at a particular temperature must move very fast, thus has a good chance of penetrating anything in its way. And being inert, don't get locked into combination with anything. Hydrogen molecules are lighter still, so move even faster - but can be caught by anything that fancies bonding chemically with them.

6th Oct 2017, 11:22 am	#24
dominicbeesley Octode Join Date: Nov 2004 Location: Hebden Bridge, West Yorkshire, UK. Posts: 1,885	Re: Helium infiltration, NOS Valves I'm guessing also that because they're inert the getter doesn't, well, get em!?

6th Oct 2017, 1:20 pm	#25
kalee20 Dekatron Join Date: Feb 2007 Location: Lynton, N. Devon, UK. Posts: 7,081	Re: Helium infiltration, NOS Valves It doesn't. Nothing combines with helium. Not even fluorine, which can be enticed to combine with xenon and krypton (and presumably radon). Luckily, proportion of atmospheric helium is very low. I do recall a manufacturer of light bulbs, making a range with super-thick glass envelopes, for use inside divers' decompression chambers. Otherwise helium diffused in, the filament was cooled more and more, and efficiency dropped.

10th Oct 2017, 2:01 pm	#26
dave cox Nonode Join Date: Jan 2009 Location: Bristol, UK. Posts: 2,062	Re: Helium infiltration, NOS Valves Hydrogen has an impressive diffusion speed at RTP (room temperature and pressure). Well above the speed of sound if I recall correctly ! dc