Zinc "whiskers" inside galvanized rigid

[tonyi]

I've recently been reading up on the metallurgical phenomenon of "zinc whiskers" (and tin whiskers).

Some months ago I encountered a run of 1" RMC that was CHOCK FULL of these things that had grown to maybe 1/2"-3/4" long over time. I hadn't heard of the phenomenon at that point and chalked it up to some fluke in the original galvanizing.

Apparently, all sorts of electronic failures can be traced back to these things:

http://nepp.nasa.gov/whisker/failures/index.htm

I'm wondering what the growth pressure of these things is, and could they possibly grow through insulation if all the angles lined up and they made a straight in run against a piece of wire. The literature suggests that a fault caused by contact of the actual whisker would blow itself clear instantly, BUT the plasma generated during that would be capable of supporting currents of several hundred amps.

 

[ron]

Unfortunately, the data center industry has had to deal with this phenomenon because of galvanizing of the pedestals and underside of the raised floor tiles. The "whiskers" would blow inside of IT equipment and mess it up!

 

[ELA]

That is very interesting about the whiskers being as large as you saw.
Most of what I have read indicated that they are very small in diameter and not much longer than 0.1 " (with Tin anyways).

The example of the raised floor whiskers indicated that the whiskers were so weak that air flow broke them off and airflow blew them into circuit areas. Seems a bit weak to pentrate insulation ?

This is a very big problem with printed circuit boards, especially now with ROHS (reduction of harardous substances -or elimination of lead in solder).
When the tin is more pure it grows whiskers better. These can easily short out the small electrical spacings on pcbs.

 

[ghostbuster]

That is very interesting about the whiskers being as large as you saw.
Most of what I have read indicated that they are very small in diameter and not much longer than 0.1 " (with Tin anyways).

The example of the raised floor whiskers indicated that the whiskers were so weak that air flow broke them off and airflow blew them into circuit areas. Seems a bit weak to pentrate insulation ?.

A previous thread (last half) has pictures and another explanation for these little devils.http://forums.mikeholt.com/showthread.php?p=672596#post672596

:smile:

 

[tonyi]

Here's a pic of some that grew in RMC. I just received this from Henning Leidecker at NASA. It looks very similar to what I saw. One of them has grown quite long....

Note - some of the literature suggests surface stress to be a factor. With rolled/welded pipe, the inner pipe surface will be pretty highly compression stressed.

Obviously any sort of maintenance work pulling new branches or replacing wire could knock these things loose, and any pressure differences between the pipe ends could send them floating around into connected equipement...