[Paddlewise] Fw: aluminum and salt water

Regarding anodizing.  Type II anodizing ("hard anodizing") occurs in a
sulfuric acid bath at 32degF using titanium racks and high DC voltage.  It
is intended for wearing surfaces and is often impregnated with teflon and is
superior to the anodizing which is typically found on most aluminum items,
such as tent poles.  Some aluminum alloys are not conducive to this process.
A sacrificial anode for steel and aluminum hulls is most often zinc.
Aluminum boats are not hard anodized.  Galvanic action between dissimilar
metals accelerates corrosion of the least electrophilic metal, which gives
up its electrons and oxidizes instead of the protected hull metal.
Friction, failure to rinse saltwater from the metal (allowing it to dry on
the metal) also accelerate corrosion.  The quality of metal finishes (ASTM
standards) is determined by the amount of time a surface can withstand a
standard salt solution spray.  Stainless steel is a beautiful thing, though
even some times of stainless rust.
Sid Taylor
>-----Original Message-----
>From: Gabriel L Romeu <romeug_at_erols.com>
>To: Dave Kruger <dkruger_at_pacifier.com>
>Cc: rdiaz_at_ix.netcom.com <rdiaz_at_ix.netcom.com>;
>paddlewise_at_lists.intelenet.net <paddlewise_at_lists.intelenet.net>
>Date: Tuesday, January 26, 1999 8:04 AM
>Subject: 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.
>>
>>--
>>gabriel l romeu
>>http://members.aol.com/romeug     studio furniture
>>http://members.aol.com/romeugp    paintings, photos, prints, etc.
>>http://members.xoom.com/gabrielR  a daily photo journal
>>
>>**************************************************************************
*
>>PaddleWise Paddling Mailing List
>>Submissions:     paddlewise_at_lists.intelenet.net
>>Subscriptions:   paddlewise-request_at_lists.intelenet.net
>>Website:         http://www.gasp-seakayak.net/paddlewise/
>>**************************************************************************
*
>>
>

***************************************************************************
PaddleWise Paddling Mailing List
Submissions:     paddlewise_at_lists.intelenet.net
Subscriptions:   paddlewise-request_at_lists.intelenet.net
Website:         http://www.gasp-seakayak.net/paddlewise/
***************************************************************************