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What's an order of magnitude among friends?

What's an order of magnitude among friends?

Posted Feb 21, 2013 21:11 UTC (Thu) by mikewd (subscriber, #46016)
In reply to: What's an order of magnitude among friends? by man_ls
Parent article: Quotes of the week

"Helium is the second most inert of all gases so it is not hard to contain. Hydrogen (as said below) or even liquid helium (as you can read on the wikipedia) are harder. With helium gas you just seal the container and it just stays there, without condensing or interacting with the walls or other gases; it shouldn't be harder than creating a vacuum."

The problem is that the diffusion rate of helium through glass or epoxy and other glues and insulators can be quite high at room temperature (as a low temperature physicist well knows). So the container needs to be all metal with a soldered or welded seal.

Mike


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What's an order of magnitude among friends?

Posted Feb 22, 2013 10:28 UTC (Fri) by khim (subscriber, #9252) [Link]

So the container needs to be all metal with a soldered or welded seal.

Well, we are talking HDDs here. They used "all metal" containers for decades now anyway. Usually they had some filters and were not welded shut, but that is minor change IMO.

What's an order of magnitude among friends?

Posted Feb 22, 2013 18:12 UTC (Fri) by magila (subscriber, #49627) [Link]

There are many openings in a hard drive which are currently sealed with epoxy or plastic/foil adhesives. The biggest is the seal between the top cover and the drive body but there are also many holes used during manufacturing. If you examine a hard drive's casing you can see where these have been sealed with circular stickers. Less visible are the openings for the spindle motor and servo/channel control lines.

Making all of these openings impermeable to He is not a minor change and will likely significantly increase the cost of the drive.


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