The phenomenon is called "galvanic corrosion"--operates on same principle as a galvanic battery--movement of electrons (electrical current) between anode and cathode in the presence of an electrolyte.
> I don't know the technical terms but steel and aluminum will cause
> corrosion when in the presence of an electrolyte such as sweat.The
> results are a chemical reaction similar to what has been
> described.Primary prevention is liberal application/reapplication of
> Nick Zatezalo
> -----Original Message-----
> From: email@example.com
> [mailto:firstname.lastname@example.org] On Behalf Of Raoul
> Sent: Saturday, June 14, 2003 11:38 AM
> To: C.R. List; Bruce C.
> Subject: Re: [CR]aluminum corrosion & pitting - Cleaners
> We always think about rainwater , and sweat , getting down between the
> tubing and the seat-post , or between the tubing and the stem .
> And I know I always think about "wash water" getting down in there .
> Since I would NEVER use a harsh cleaner , I'd never really thought
> what could possibly be in the very worst-case "wash water" .
> I received a very nice , used-but-still-pretty-fresh , 1978 Proteus
> bicycle , not long ago .
> The seller had a horribly hard time getting the seat-post out . I
> personally have never seen a Campagnolo Record seatpost as badly
> corroded as
> this one . I looks as if it is made from old , partially decayed ,
> oyster shells . It is obviously no longer solid metal at all .
> made of many-many layers of horribly corroded aluminum . There is
> physically no way that it could possibly go back into the seat tube from
> which it emerged . The seat-post quite clearly "blossomed out" ,
> opened-up , after it was pulled out . What a mess .
> The good news is that the aluminum sacrificed itself for the good of the
> seat tube . The steel looks great . Although , the patterns are
> clearly a match . So yes , I am sure that this post came out of this
> tube .
> The stem was not too badly affected , somewhat , not much .
> Puzzling .
> I had not thought about someone using some sort of caustic cleaning
> , or solutions .
> Go to the auto parts store . Look at the various cleaners . They do
> make a major big deal about either being safe for use on un-coated
> , or , NOT being safe and NOT to be used on aluminum .
> Just never thought about that one before .
> AND , what is available at car washes today , can be VERY dangerous
> delicate finishes , and delicate metals . Stand down-wind of a
> car wash , while they are spraying their special "ultra-cleaner" or
> whatever they may call it . It does NOT smell like detergent and
> . It smells much more like some kind of toxic paint remover .
> The new "no touch" car washes use some seriously HARSH cleaners .
> Bicycle shop people have always had to remind customers NEVER to use a
> wash place , for cleaning their bicycles .
> Now it's much more true than ever before .
> Raoul Delmare
> Marysville Kansas
> ----- Original Message -----
> From: "Scott Sweeney" <email@example.com>
> To: <firstname.lastname@example.org>
> Sent: Saturday, June 14, 2003 10:11 AM
> Subject: [CR]aluminum corrosion & pitting
> Does anybody know what causing "pitting" of alloy parts? I've noticed
> pitting on the bases of Cinelli stems, and seatposts where they were
> inserted. These are typically greased fittings that are really puzzling
> I know certain detergents that are high alkali cleaners (high PH) are
> caustic to soft metals, that maybe the previous person cleaned the bike
> some kind of cleaner that was corrosive. That is my only guess. I'm
> you've all noticed this too. Please note that what I'm talking about is
> "pitting" and not the typical scratches that take place. Anyway, I'd
> to be able to prevent such pitting from occuring in the future. Any
> would be appreciated.
> Scott Sweeney
> Salinas, CA