From: email@example.com (Glen Walpert)
Subject: Re: Side effects of potting compound !
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Date: Thu, 07 Nov 2002 13:00:03 GMT
NNTP-Posting-Date: Thu, 07 Nov 2002 08:00:03 EST
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In article , firstname.lastname@example.org (Bob Wilson) wrote:
>This was also my own experience. In theory, none should appear at all since
>a) copper is unaffected by common acids, and b) there should be no water
>present to ionize the acetic acid produced. But of course, nothing is
>>Allowing it to cure in free air produced *no* corrosion whatsoever so
>>matter what else was done.
>Exactly. Unfortunately, too many people forgot their Grade 9 science, and
>got scared when they heard that normal RTV generates acetic **ACID**
Your error is basing your understanding of corrosion on that 9th grade
science. Just because copper does not instantly corrode when dunked in acetic
acid, does not mean that acetic acid will not contribute to long term crevice
corrosion - it will. And you cannot avoid the persence of water, it is there
in a layer many molecules thick on all surfaces exposed to the atmesphere.
Try reading the ASM Metals Handbook Volume 13, Corrosion, if you want to
understand how electrolyte aided crevice corrosion occurs, and why the
electrolyte in itself does not need to be chemically corrosive to cause
corrosion. Any other modern book on corrosion will explain this also.
But like I said before, this is a long term effect which occurs over a period
of years, depending also on the inevitable porosity in the gold plating on
the trimpot wiper, and since long term reliability is not an issue here ...