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In article <4345@druco.ATT.COM>, jhs@druco.ATT.COM (J H Shore) writes:
> > Has anyone tried playing with parasitic anodes for rust prevention of
> > automobiles?  I have seen several likely gimmics that you "bolt-on"
> > and forget.  

	Corrosion mechanisms and their control is a very complex issue.
Without getting into any specific detail or calculations, my intuitive
opinion is that in an automobile: (1) no significant amount of corrosion
occurs as a result of potential difference between exposed metal areas;
(2) the surface area beneath a vehicle is significantly "small" as compared
to those situations where corrosion control methods are usually implemented;
(3) the physical contours beneath a vehicle are so complex that any passive
or active anode arrangement will be ineffective.
 
> > I was wondering if there is any simple way to make a system that
> > *really* works for protecting some of the parts that tend to collect
> > water, such as on the bottom insides of the doors.  I was going to try
> > a long of cloth-wrapped zinc wire attached to +12v (through a several
> > k-ohm resistor).  Anyone have any other pointers or insight?

	Forget it, and don't waste your time.

> Naval ships--and probably merchant marine ones as well--use large 
> zinc bars bolted in strategic places both within and external to the
> hull to minimize electrolytic action associated with prolonged 
> exposure to sea water.  None use an active potential (that I know of).

	There are shipboard corrosion control systems which apply an active
potential to a corrosion control anode.  An example of such a system that
I have seen is called "Capac", is manufactured by Electrocatalytic Ltd.
of the UK, and is sold on a world-wide basis.  I have seen Capac rectifiers
in sizes between 25 and 600 amperes.

	Also, shipboard corrosion and its control is a totally different
environment from that of an automobile (after all, the ship is continuously
and uniformly immersed in the electrolyte!), and no parallels should be
drawn between shipboard corrosion and the discussion about automobiles.

<>  Larry Lippman @ Recognition Research Corp. - Uniquex Corp. - Viatran Corp.
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