Will A Bonded Zinc Protect My Automobile?

[Submarine Tom]

From CDK's thread on zincs.

Would a marine zinc, screwed into my cars frame, interrupt rusting.

Some good arguments have been made for and against it's efficacy.

-Tom

[michael pierzga]

Your car is constructed of zinc coated steel for galvanic protection. Perhaps spray zinc to repair localized damage to steel. This is how they repair and supply galvanic protection on concrete steel reinforced bridge and jetty structures. And remember galvanic corrosion is only one form of corrosion attacking your car. Crevice corrosion, pitting corrosion and normal cosmetic corrosion when you scratch the steel and expose it to oxygen. Zinc would not address this.

http://www.a-sp.org/database/custom/...Protection.pdf

[gonzo]

Zinc migrates on galvanized steel and is self-healing to an extent. There isn't enough electrolyte to make zinc go from an anode to wherever the scratch or ding is.

[marshmat]

Tom- no, a sacrificial electrode (or an active impressed current system, for that matter) doesn't work on a car. They only work when the sacrificial zinc and the metal to be protected are immersed in a common electrolyte. In a boat, salt water is this electrolyte. In a car, there's no medium in which the ions can migrate.
Your best bet for something rust-prone and not immersed in water (eg. a car) is a water-displacing light oil, such as Rust Check. There's a wealth of scientific evidence to support the claim that annual treatments with water-displacing light oil rustproofers will hold off rust for many decades, if not indefinitely.

[MikeJohns]

Here's the thread [Revelations about zinc electrodes.

Read my comments there. The idea you could protect your car or any other steel structure subject to a thin film of moisture this way shows a misunderstanding of how cathodic protection works.

[Submarine Tom]

Well, the bottom line here is, you need a closed loop circuit and simply screwing a zinc into the car frame does'nt create one.

BUSTED, it doesn't work.

-Tom

[cthippo]

Cathodic protection...You keep using that word. I do not zinc it means what you zinc it means.

~Inigo Montoya

[MikeJohns]

Originally Posted by cthippo

Cathodic protection...You keep using that word. I do not zinc it means what you zinc it means.

~Inigo Montoya

First define an electrochemical cell as two attached metals at the same potential in an electrolyte. Then the definition in electrochemical cells is simple. The exposed electrode where the Cations are reduced is always the Cathode. There are no exeptions.

When you attach a zinc to a more noble metal in an electrolyte you have created an E.C. cell.

Cathodic protection means the reduction reaction rather than the oxidation reaction occurs at the protected surface. That's what the attached zinc Anodes do, they act to cathodically protect the immersed steel.



Where people get confused with al this is when you separate the metals in the electrolyte and they are no longer at the same potential, AKA a battery. Now the Anode and Cathode are referred to by their relative potentials.

The confusion arises when you try and apply the battery model to the EC cell where both metals are at the same potential.

So as a rule Anodes are positive terminals and Cathodes are negative terminals, but when there is no terminal and the different metals are at the same potential and electrically attached, then the Cations are attracted to the Cathode and the Anions are attracted to the Anode.

[hoytedow]

Originally Posted by Submarine Tom

Well, the bottom line here is, you need a closed loop circuit and simply screwing a zinc into the car frame does'nt create one.

BUSTED, it doesn't work.

-Tom

Of course, when you are driving on a puddly previously salted road, the zinc on the frame can't hurt. The water and the electrolyte are both there, so the zinc might actually do some good until you get the salt rinsed off the vehicle. I zinc its a good idea.

This may work better than screwed-on sacrificials.:http://www.clearcoproducts.com/cold_...ze_sprays.html

[Submarine Tom]

Of course zinc coating (galvanizing) works, that wasn't my question.

-Tom

[hoytedow]

Then my answer to the original question is "Part of the time".

[Submarine Tom]

Okay, which part?

-Tom

[hoytedow]

When the bare metal and the zinc are in electrical contact by being bathed in electrolytic salt water. Any time the zinc is dry and the body panels are wet there is no protection, or if the zinc is wet and the panel is wet but they in 2 different wet patches unconnected the panel is not protected. When everything is dry there is no protection.

[Submarine Tom]

Oh, that part.

Nice graphic! I love the snowy background. You artistic type you.

Or did I read that wrong and they're chunks of SALT!

-Tom

[hoytedow]

Sea ice.