Clarifying corrosion
Hi again Brian,
Let's leave the sealant question aside for a moment, and address some of the points in your most recent letter. Stainless does not, in fact, "corrode from the inside out", or at least not the way I meant it. Crevice corrosion has to eat into the metal from a surface; it can't start on the interior. So when you find a crack, it will always have propagated from a surface. That's why we polish metal surfaces, and construct them from corrosion-resistant alloys: to prevent corrosion from affecting the surfaces.
Electrolysis is a specific kind of corrosion, quite distinct in cause from crevice corrosion. Electrolysis is a galvanic reaction fueled by live current. It can coexist with crevice corrosion, as can chloride corrosion, stress corrosion, etc., but it definitely should not be confused with it. And if you see evidence of electrolysis in a swage, you probably have much more serious issues than cracks, anyway.
Now back to sealants. It is true that most silicones are mildly acidic, but to a trivial degree, and even then only before it has cured. Automotive silicone is usually low-acid, because gaskets are more readily affected by acidity than large chunks of stainless. But there's a better reason not to use any type of silicone in a terminal: it is less efficient at maintaining adhesion than other goos, particularly over wide temperature changes. We've found that 3M's 4000 or 101 are far more stable, yet not so adhesive that they make reusing the terminals diffcult.
Arenyi noted, in a previous letter, that "...wires always break near the open end of the swage...". If only it were true. Many times we've found broken wires inside swages, a consequence of corrosion from water intrusion.
Fair leads,
Brion Toss
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