Hello, On Tue, 21 Nov 2017, Carlos E. R. wrote:
El 2017-11-21 a las 22:12 -0000, Wol's lists escribió:
On 21/11/17 21:46, Lew Wolfgang wrote:
On 11/21/2017 01:16 PM, Carlos E. R. wrote: Note that (and yes this does sound weird) Helium is actually a metal.
You can get iron as a gas, too :-)
And it has all these weird properties that makes it useful for things like this. As mentioned, all gases have the same number of molecules per volume at any given temperature, so replacing Nitrogen (atomic weight 28 per molecule) with Helium (atomic weight 4) abrades less energy off the platter (lower friction :-) and the draught can't disturb the heads so much.
They do need some drought, to fly. With no friction (vacuum) the heads would crash.
Question is: how much? :)
The implication is the hydrogen (weight 2) would be even better, but I suspect the fact that helium is a noble gas has something to do with it.
It burns. It burns very well, even explode in the right mixture. I know that from personal experience :-)
And it is more difficult to contain for 5 years.
As I said, Helium is a metal which is probably why, what heat is generated, helium conducts it away much better.
Maybe. I know nothing about why different gases may conduct heat differently, even if they do.
After some Wikipediing: https://en.wikipedia.org/wiki/Covalent_radius https://en.wikipedia.org/wiki/Van_der_Waals_radius https://en.wikipedia.org/wiki/Molar_volume https://en.wikipedia.org/wiki/Thermal_conductivity cov.r VdW r Molar volume Density Th.cond pm pm 10^~6 m3/mol kg*m^~3 W/(m*K) H: 31±5 120 11,42(solid) 0,0899 0.1805 He: 28 140 21,00(solid) 0,1785 0.1513 N: 71 155 13,54(solid) 1,250 0.02583 From the He-"uses" section: "Helium is used for many purposes that require some of its unique properties, such as its low boiling point, low density, low solubility, high thermal conductivity, or inertness." Couldn't find stuff on molecular H_2. I'd guess a H_2 molecule is larger. Hm. If I read that right, a H_2 molecule has a radius of twice the covalent radius of H, i.e. ~62, i.e. it is larger than that single He atom flying about. And He is just about always single. And H just about never and is "corrosive", cue your good ole NiMH accumulators. And N can get very nasty if not in a pair as N_2[1] and N is about 6 times less thermally conductive as He. He though is AFAIK as inert as it gets. -dnh [1] http://blogs.sciencemag.org/pipeline/archives/2013/01/09/things_i_wont_work_... "The compound exploded in solution, it exploded on any attempts to touch or move the solid, and (most interestingly) it exploded when they were trying to get an infrared spectrum of it." I suppose you could say "if as much as a gnat farts ... in the next room ..." -- After a prolonged soak the parts required to fix the FM could be separated from a rather indescribable, um, something. With a little more resolve it might have walked off and started a certain software company, but maybe it was already too smart for that. -- Rik Steenwinkel, in asr, on the meeting of a Nikon FE and a jar of yoghurt -- To unsubscribe, e-mail: opensuse+unsubscribe@opensuse.org To contact the owner, e-mail: opensuse+owner@opensuse.org