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Magnet Destruction

04/26/2016 6:35 PM

Just started a new project at work, building on some work done by a university. The device will be a small gas sampling valve working within a high vacuum system. The university have made prototypes & an essential component is a Neodymium magnet. I was surprised to be told that the current valve is not suitable for use with hydrogen because the Neodymium breaks down in the presence of hydrogen, literally breaks into small pieces in about 30 minutes.

Does anyone know the mechanism of this breakdown? I don't understand the chemistry but I know that hydrogen is a strong reducing agent, could it be that the Neodymium structure is held together by oxides which are destroyed by the hydrogen. If this is the case, how do I protect them? The magnets are usually nickel plated so it appears that the nickel does not do the job. Whatever I use must be OK in a vacuum environment.

I found a video which shows the breakdown of Neodymium in hydrogen but unfortunately gives no explanation.

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#1

Re: Magnet destruction

04/26/2016 6:53 PM

Nd magnets are sintered and usually coated with some kind of polymer or Ni-based shell.

I have used epoxy-coated ones before. Mfgr of something like that might have info on compatibility with H2.

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#2
In reply to #1

Re: Magnet destruction

04/26/2016 7:07 PM

"Most of the rare earth elements (neodymium, dysprosium, samarium, etc.) absorb hydrogen into the structure resulting in expansion and cracking of the material which is referred to as decrepitation. Therefore, neo magnets are not recommended where exposure to hydrogen is likely. - See more at:

http://www.arnoldmagnetics.com/en-us/Products/Neodymium-magnets#sthash.VULWIG5t.dpuf "

Ref: http://www.arnoldmagnetics.com/en-us/Products/Neodymium-Magnets

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#3
In reply to #2

Re: Magnet destruction

04/26/2016 7:21 PM

Thanks!

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#5
In reply to #2

Re: Magnet destruction

04/27/2016 6:25 AM

Thanks for that, I'll contact them to see if they have an equivalent magnet to survive in hydrogen.

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#10
In reply to #5

Re: Magnet destruction

04/28/2016 12:57 PM

May be James Stewart has some bright explanation on this.

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#4

Re: Magnet Destruction

04/27/2016 12:45 AM
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#6

Re: Magnet Destruction

04/27/2016 9:25 PM

I have a lot of neodymium magnets plated with nickel. They're fine when they're new, but after a while the nickel plating comes off. I have some gold plated ones that are still in very good condition, although they have not seen any hard use. They are more expensive.

Neodymium Iron Boron magnets are very susceptible to corrosion and need to be coated with some material.

Here is some information on some of the common coatings. I don't know how these coatings stand up against hydrogen.

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#7
In reply to #6

Re: Magnet Destruction

04/28/2016 4:09 AM

Thanks, good information. Gold is OK in vacuum although I would have to consider what might be trapped under the coating within the magnet structure. Price is not a problem, these finished devices will not be cheap.

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#8
In reply to #7

Re: Magnet Destruction

04/28/2016 4:53 AM

I m really guessing here, but a sintered metal is basically full of tiny holes.

With a vacuum, even when plated, you might damage the plating as the air inside expands and contracts as the vacuum is applied and stopped, applied and stopped. Maybe damaging the plating over a time period....

If I was trying to make them gas proof, I would look at something like a high pressure "filling" of those gaps with a thin liquid epoxy resin or similar. That way, no gas to expand, though I am unaware of how hard epoxy reacts under a vacuum, there may be something better around....

Then clean off the outside and plate.

Though there may be no need to plate at all if a thin coating exists over the metal... but it would still need to be tested and checked.

Just a thought...

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#9
In reply to #8

Re: Magnet Destruction

04/28/2016 6:09 AM

Something like that could work, there are impregnations which are OK in vacuum.

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