Re: [Paddlewise] aluminum and salt water

Dave Kruger wrote:
so depends on [fill in the blank]."  Maybe a story will help explain.
> 
> Out here, they make gill net boats (for saltwater service) out of one of
> the 5000-series aluminum alloys (don't know which one), so I scurried off
> to my buddy who makes those boats when I wanted a chunk of
> corrosion-resistant aluminum to make a skookum rudder horn for my Folbot.
> Much to my surprise, if the horn is left, wet, in contact with the
> seemingly-cheesy Folbot aluminum castings, it erodes badly at the contact,
> and the castings *don't* corrode.  Why?  I don't know.  I could speculate
> about it, but the value of the speculation would be exactly equal to what
> the readers of this list paid for it.  The gill net boats hold up well in
> marine service (years and years).  Go figure.
> 

One thing I have heard to prevent galvanic erosion is to attatch a
disimilar metal which reacts more acutely to the process.  this is
referred to as a sacrificial anode.  I believe that copper is a common
material for this, though I can't be sure.
> 
> Oh, one other thing, anodizing usually produces some very toxic wastes,
> which cost a lot of money to deal with properly.  Feathercraft may have the
> anodizing done someplace special because the diseconomy of a small-scale
> operation (which has to deal with proper disposal of those wastes just like
> a larger operation) has driven a lot of smaller anodizing places out of
> business.  Feathercraft is not the kind of firm to have it done someplace
> which is cheaper because the anodizer deals improperly with the wastes.
> 
> As a chemist who deals with waste disposal issues in a very small academic
> lab, I'm very conscious of the impact correct disposal has on the cost of
> my operation.  Sometimes costs way more than the raw ingredients we buy.
> 
> --
> Dave Kruger

The anodizing bath is ususally an acid, similar to the type in auto
batteries.
The pre-etch solution is sodium hydroxide (lye).
The dye used for color may be an assortment of chemicals, most of which
are fairly toxic as well.

Dave is ver right.

-- 
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