Neodymium material compatability 1

[aspearin1]

I came across a general "what not to do" page on a website that basically said not to put NdFeB magnets in any fluid, (including water), without having them in a sealed chamber. It also mentions to avoid acids, alkalis, and oil. I am involved with a project that uses the NdFeB magnets in a "sealed" rod for use in removing tramp iron from aqueous systems. I recently opened up one of these rods to find that there was significant leakage, and the magnets were exposed to the elements. I need to know what this may mean.

Can anyone offer more specific cause and effect references for NdFeB contact with incompatable fluids? Do acids and alkali react violently or just corrode? Any help is appreciated.

aspearin1

 

[nbucska]

If in doubt,protect it.
Leakage means you failed to protect it.

You have to decide if your job is to design or to research.

If the later, you may want to include the effect of temperature, mixtures of different materials etc.





<nbucska@pcperipherals.com>

 

[aspearin1]

I consider it my job to know.... If there is a system failure, I wish to know what that failure means. Research and design share very much the same bed.

aspearin1

 

[nbucska]

The bosses usually have different job-description...

<nbucska@pcperipherals.com>

 

[aspearin1]

Well, from an FMEA standpoint, how would I know a severity rating without knowing what a failure may cause? We can reduce probability, but never eliminate the possibility.

aspearin1

 

[IRstuff]

The severity is also dependent on the "effect" fo the failure, i.e., will it cause discomfort, dismemberment or death.

Therefore, your safety analysis would take that into account and your efforts are supposed to be geared toward minimizing fatal possibilities first, then addressing equipment failures.

TTFN

 

[sreid]

Clearly Neo magnets corrode in air and propably corrode more quickly in water.

Most metals corrode more quickly in acids or bases. Neo magnet dust can catch fire so I suppect that there could be a problem in strong acids or bases.

 

[EdStainless]

Exposed to almost any fluid Neo magnets will corode. There are two results. First the corrosion products are not magnetic, so you will loose strength. Secondly the corrosion products take up a lot more volume than the original material. Your containment may swell and even burst.
In some acid or strong oxidizers this will happen very fast and can produce significant amounts of heat (glowing red hot).

Corrosion never sleeps, but it can be slowed down.

 

[gphatch]

Uncoated / unprotected NdFeB [a.k.a. Neo] magnets are highly susceptible to corrosion for two reasons:

1) The grain boundaries in the material contain among other things, Nd-rich phases which are highly susceptible to oxidation and corrosion. The corrosion products can cause grain fall out and other problems, leading to more paths into the body of the magnet for corrosion to occur. There is also some evidence that you get an additional electrochemical [corrosive] effect due the significant electronegativity differences between constituent phases, too.
2) The bane of any Neo magnet is hydrogen. Hydrogen reacts with the phases within the Neo material to form hydrides, very quicky. This process is called hydrogen decrepitation [HD] and is actually used to break up bulk alloy raw materials when magnets are being produced. Even the slightest presence of hydrogen, from acids or other chemicals, will accelerate this HD process. There is a significant volume expansion associated with this process and this will lead to rupture of magnets through the introduction of internal stresses.

Hope this helps

Gareth P. Hatch, Ph.D.
Director of Technology
Dexter Magnetic Technologies

 

[GraviMan]

Hmmm, now you got me worried Gareth. I designed a mag circuit, a few years ago using NdFeB mags, for low distorsion speaker drivers (hobby - see link). The copper and mag circuits were hydrogen recrystalised, to remove residual machining stress. The buttons magnets were sealed in the assy with epoxy resin, since I suspected long term corrosion problems.

Are you saying that any residual H2 from the recrystallisation process is likely to cause problems? The assembly can "breath" relatively easily, and I still enjoy the prototypes sound. It there likely to be a period of expensive cracking sounds?

http://hometown.aol.co.uk/martingarrish/myhomepage/hobby.html

Mart

 

[EdStainless]

Don't worry GraviMan, The is no residual H2 in the parts that you had annealed.
Epoxy coating should be good enough to protect the magnets from common evironmental exposure.

= = = = = = = = = = = = = = = = = = = =
Corrosion never sleeps, but it can be managed.

http://www.trenttube.com/Trent/tech_form.htm

 

[gphatch]

GraviMan,

I would agree with EdStainless' assessment - with the epoxy coating I doubt you'll have any problems.

Gareth P. Hatch, Ph.D.
Director of Technology
Dexter Magnetic Technologies

http://www.dextermag.com

 

[GraviMan]

Thanks Gareth and Ed,

Nice to know I'll have distorsionless sound for years to come...

Mart