Subject: RUST PREVENTION FOR CARS

From: [email-masked] (John Burt)
Date: Tue, 7 Feb 95 22:58:00 -0600

KP> I have heard of an electronic unit produced in USA which prevent
KP> cars from rusting. Can anyone give some information. Does it work?
KP> Price etc.

I believe you are referring to cathodic protection.  Rust is corrosion
(oxidation) of the iron.  In oxidation, the metal is known as an anode,
and it loses electrons.  The electrons have to go someplace; they flow
to a cathode, where reduction occurs.  (reduction is when electrons are
received)  Oxidation and reduction always occur simultaneously.

If you consider this oxidation-reduction process (known as redox) you
might realize that this is an electrical circuit, with electrons flowing
from the anode to the cathode.  In order for electrons to flow, there
must be a potential difference (difference in voltage) between the anode
and the cathode.  This voltage difference is what drives the redox
reactions.

What we have so far is:  An area of the steel (iron) has a low
electrical potential, so electrons flow to an area of more positive
potential, leaving positive iron ions which readily combine with
negative oxygen ions, creating rust.

One method of controlling rust is to electrically connect the steel to
a metal with a more negative equilibrium potential.  This metal is
known as a "sacrificial anode" and it is often zinc.  The sacrificial
anode will oxidize and save the steel.  Zinc anodes are often used to
protect steel boats and buried pipelines.  This is also why zinc is
used to galvanize steel -- theoretically the zinc will have to be
consumed before the steel starts to rust.

The electronic method of cathodic protection uses an existing source
of electricity (such as the car's battery) along with electronics
to regulate voltage and current, to keep the protected steel at a
safe positive potential so that corrosion will not occur.

An electronic rust control system is sold by J.C. Whitney & Co. of
Chicago.  (They are also known as Warshawsky & Co.)  Their phone
number is (312) 431-6102.  Their address is 1916 South State Street,
PO Box 8410, Chicago, IL  60680.  Price is $150 - $200, and note
that my catalog may be a year or two old.  (I am only passing this
information along -- I have only seen this product in the catalog,
and I have no idea how well it works -- or IF it works at all.)

Things to keep in mind about cathodic protection:  A wire will be
connected to the steel that is being protected.  The other end of
this wire will connect to either the sacrificial anode, or to the
electronic control unit.  (By the way, the electronic units still
use anodes; they are sometimes referred to as "inert" anodes, because
the electronics provides the voltage potential for protection)
The point where that wire attaches to the steel may be very well
protected from corrosion; however, another point on the same piece
of steel may not be as well protected, because it is very difficult
(impossible?) to make electrical current flow evenly throughout
a car body, for example.  If current is not uniform, potential will
not be uniform.  It seems like the ideal situation would be to have
a very large number of connections, evenly distributed over the car
body.

Another possible problem with the electronic method of cathodic
protection is that too high a potential is placed on the steel
being protected, hydrogen could be absorbed by the steel, which
could significantly weaken it.  This condition is known as
hydrogen embrittlement.

PLEASE NOTE:  I am not an expert on cathodic protection, nor am
I an expert on electrochemistry.  I became curious about this
subject a few years ago, and this is a summary of some literature
searches that I did at that time.

John Burt   N9DVM
[email-masked]

 * RM 1.3  * Eval Day 18 *

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From: [email-masked] (Jeff Danda)
Date: Thu, 9 Feb 1995 01:14:22 GMT

>If you consider this oxidation-reduction process (known as redox) you

I used to go underneath the car with a brush and some old motor oil and 
paint away.  Looked like hell, but always prevented rust.

Jeff