DDC Fixed Head Disks

dwight elvey dkelvey at hotmail.com
Sun Jun 10 11:47:07 CDT 2007




>From: "Chuck Guzis" <cclist at sydex.com>
>
>On 9 Jun 2007 at 21:43, jd wrote:
>
> >> Helium is a very good thermal conductor but I would suspect that
>it is used
> > because it is cleaner and dryer than air and nitrogen and truly inert 
>and won't
> > chemically react with the medium. The helium was likely under pressure 
>to reduce
> > the chance of air getting in. Since it can leak out much faster than 
>nitrogen
> > and air, thanks to the physics of helium, the seals and sealing surfaces 
>must be
> > in excellent condition. But no matter how good the seal, helium still 
>leaks out
> > so it needs to be replenished from time to time.
>
>So why wasn't another noble gas used, such as argon?  I don't doubt
>that helium might have been used, but I don't understand why.
>
>
Hi Chuck
The only two things I can think of where mentioned by others. One
was thermal conductivity and the other was friction. Helium has almost
zero friction.
Still, the stuff leaks out of things so fast. Even solid surfaces.
I find it funny that it is cheaper than argon. There is a lot of
argon but I'd guess the extraction from natural gas, where it
is undesired for burning, makes helium cheaper than argon that has to
be intentionally removed from air. Two percent of air is argon
as I recall.
Dwight

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