From: "E.J. Totty", [EMAIL PROTECTED]
>I'm no metallurgist, but how it was explained to me is something like this -
>moisture ( from the chemical reaction of burning powder ) plus molybdenum (
>a sulphide ) plus stainless steel can set up an electro-chemical reaction
>path which causes "crevice erosion" in the stainless steel - this is very
>noticeable where angular machining has been done ( rifling ) - this was the
>basic explanation given to me by a surveyor colleague to explain the virtual
>total destruction of threading and of more than half its 1 3/4 inch
>thickness, on a six month old marine grade stainless steel bolt - for some
>reason the nut was not affected. I am now very wary of moly anywhere near
>stainless.
>Over to the more scientifically inclined :-)
>David M ( Sussex )
Steve, & David,
Rather interesting, that. If the bolt and the nut were of the same
alloy composition, then there should not have been significant differences
in the corrosion rates, simply because the corrosion cell would have been
common to both components. A corrosion cell is set up on a metallic surface
where there is sufficient moisture able to linger, and oxygen. The moisture
will after a fashion begin to obtain sufficient components to make up an
electrolyte.
If both components were at the same potential electrically, then
it is possible that the nut may have had more nickel than the bolt, or
as the last article below infers, the nut was passivated.
The is also the aspect of thermo-galvanic corrosion, as it might
be applied to firearms, under that heading below.
Galvanic corrosion is the most common type of corrosion where
metals are concerned. Some reading here is in order.
Check these out.
http://www.corrosionsource.com/learningcenter/galvanic.htm
http://www.diveweb.com/maritech/features/uw-su99.01.htm
http://www.ocean.udel.edu/mas/masnotes/corrosion.html
http://www.corrosion-doctors.org/Aircraft/galvdefi.htm
http://www.caloritech.com/catalog/page202.htm
http://corrosion.ksc.nasa.gov/html/galcorr.htm
http://www.kelleytech.com/bulletins.html?article=2912
Thermo-galvanic corrosion:
http://www.alu-info.dk/Html/alulib/modul/A00109.htm
http://webmall.ucbiz.com/power/contents/dictionary/dictionary.htm
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