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Comment by burke | Hacker News Reader

I remember hearing somewhere that helium will slowly leak through whatever vessel you try to contain it with. I wonder if that (is true, and if so whether it) imposes some kind of maximum life on these drives. Or maybe this is only hydrogen that is this problematic.

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> I wonder if that (is true, and if so whether it) imposes some kind of maximum life on these drives.

It does. Most helium-filled drives expose a SMART attribute (ID 22) for how much helium is remaining.

No expert, but it seems to make sense that helium is particularly hard to contain based on molecular diameter:

  Hydrogen 2.75 Angstroms 
  Helium 2.18
  Argon 3.67
  Oxygen 3.64
  Nitrogen 3.64
  “Air” 3.74

Yet it takes it weeks or months to leak out (I suppose it'd be more accurate to say 'slip between' the other molecules) of an extremely thin mylar balloon. I am sure it's an engineering challenge to keep it inside a small metal box, but it seems possible, at least. After all, the reserves we have have just been stuck in the ground, without managing to leak into the atmosphere.

Fascinating - I had expected helium to be a larger molecule than hydrogen.

The given value for hydrogen is for hydrogen gas (i.e. H₂), while helium is just a single atom.

That's what you would expect, though. Helium gas is "He1", hydrogen gas is "H2".

I think that was their point: hydrogen gas is diatomic, so it makes intuitive sense for it to be larger than helium

There's a detailed explanation here: https://chemistry.stackexchange.com/questions/115363/is-a-hy...

Edit: Oops. Still relevant since it's H2 in play here, but yes, not hyrdrogen vs helium.

I think that explanation is only about Hydrogen molecules and hydrogen atoms, not Hydrogen vs. Helium.

There's a free textbook available here [1] that explains that atomic sizes decrease across the periodic table and increase down. In short, it decreases across a horizontal period because more electrons are in the same orbital shell (really a cloud), increasing the negative nuclear charge of the cloud, which is more attractive to the positive atomic nucleus, so the whole cloud is squeezed together, making the whole atom smaller.

[1]: https://chem.libretexts.org/Bookshelves/General_Chemistry/Bo...

This seems unintuitive as I would expect one electron by itself to be more closely attracted to a positive nucleus instead of when there are two or more fighting to remain in "orbit".

Your definition would make sense to me if you can think of electrons adding to an over all single electrical charge instead of individual electrons, but in that case, I have to ask, what is the original reason a single electron is repulsed by the atom. I.E. why does it stay so far away until more electrons are added. What is the force keeping electrons from falling into the nucleus in the first place and have an "orbital" or "cloud" at its set distance (like one Angstrom or Bohr)?

My instinctive guess is that it has to do with the spins of two electrons "balancing" each other keeping them closer to the nucleus.

My understanding is that spin leads to a slightly different electrical force between up and down spinning electrons due to weak force symmetry breaking or singing to that effect. It's more like they have tiny electrical differences rather than canceling out any charge unless I'm mistaken.

I'm getting this from memory of my high-school chemistry classes, so be careful.

Back then the explanation was that since the He nucleus has twice the positive charge as the Hydrogen one, it'd bring the electrons a bit closer. Both atoms have a single S orbital, He with two electrons.

Also, atomic Hydrogen won't remain atomic for long - it'll quickly connect to another Hydrogen so it's S orbitals share electrons.

Again, from memory of my high-school chemistry classes (30+ years ago).

Wouldn't the real problem be other things leaking back in? If the helium just leaves, that's a vacuum. If only helium can pass, then it's going to stay helium in there.

Helium can leak into and between crystals in the metal inside the container and container itself. That process changes dimensions and mechanical properties of construction.

In this particular case I see it as a planned deprecation, sort of.

drives like this will typically be rated for a 5yr operational life.

If there is leakage, I wonder how long it would be before the data could not be recoverable? Could one transplant the platters and 're-charge' the Helium? Or just somehow recharge the old disk? Because unless / until we get some cheap lots-of-bit storage, all the 'stuff' we're generating will not be, in effect, archivable. Is this right?

Yay back to syringes and weird jigs and refilling our computing accessories with weird chemicals.

Dunno, but disks are consumable items - don't kid yourself otherwise.

I expect some drives to fail within 5 years, but I have many that still have data from much longer ago.

It would be a disconcertingly new phenomenon to find every drive in some old archival NAS failed simultaneously, or every one In a collection of external drives, because all drives last exactly 5 years with little variation, even when switched off, due to helium loss.

I believe helium is used due to it being more effective than air at removing heat. Vacuum is significantly less effective (as in, no convection in a vacuum)

I heard that it was because helium filled drives have less drag on platters (thus, are more efficient) than air filled drives.

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