Cathodic protection for frames

[Brian Monticello]

Has anyone ever heard of cathodic protection? When I wasn't sleeping in chemistry class I remember learning about how corrosion and rust is basically the result of a chemical reaction caused by flow of electrons (basically a super low voltage battery created by the conducting metal and the air and water).

From a high level cathodic protection involves providing a donor metal so that the donor metal corrodes before the base metal corrodes. I believe this is used extensively for large scale equipment like ships - especially in salt water.

Does anyone know of a product like this for automobile frames or non-corvette bodies? Is there any reason why this theory can't be applied to Corvette frames?

[Duke W.]

Re: Cathodic protection for frames

Anodic or Cathodic protection is achieved by "plating out" a non-conductive material on the anode or cathode and is particularly important in cooling system protection because you have dissimilar materials in continuous contact with a weak electrolyte. This is why antifreeze should be changed periodically because the corrosion inhibitors are depleted and the clock runs continuously as long as there is liquid in the system including storage periods.

Frames can be subject to electrolytic corrosion particularly if they are in contact with an electrolyte. Water itself is a weak electrolye, but add salt to it, and frames can rust out.

Since our vintage Corvette are not typically driven every day and subjected to highly corrosive environments. electrolytic corrosion of the frame is probably not a big issue, so a good rust preventative primer and top coat paint are usually sufficient to provide long term protection to both surface oxidation and electrolytic corrosion. especially if the cars are primarily driven in dry weather.

Duke

[Doug Flaten]

Re: Cathodic protection for frames

It can't really be applied to an automobile frame. There is no continuous electrolyte. As you mention, a ship has seawater electrolyte.

There are some products for cathodic protection of radiators. Sacrificial anodes must have a "clear view" of the metal they are protecting. All of the tubes etc act as baffles that preclude complete protection. The anode may protect the radiator neck where it is installed, but will protect little else. In pressure vessels, we place anodes on each side of any baffle.

[Dale Pearman]

Re: Cathodic protection for frames *NM*

[Joe C.]

Re: Cathodic protection for frames

Brian:

The entire frame would have to be fully immersed in an electrolyte in order for the cathodic protection to work.This principle is also extensively used in underground piping, where the soil is the electrolyte, the pipe is the cathode, and the donor metal anodes(usually zinc) are braised onto the pipe at regular intervals along its length, and buried along with the pipe.

Joe