The Rusting Process:

Rusting is a persistent electrochemical reaction that is hard to stop. Steel will rust. The reason rust is so hard to control is that steel has a higher chemical potential than ferrous oxide. Steel mills expend a great deal of energy driving off oxygen in the steel-making process. As a result, a large amount of potential energy is stored in the steel and the iron is thermodynamically "anxious" to return to iron oxide. Rusting takes place through an electro-chemical circuit between an anode, where iron leaves the steel, and a cathode, where electrons leave the steel. Between the anode and cathode there is an electrical potential difference in the metal.

High localized stresses in steel changes the electrical potential. A point of applied stress becomes an anode. This phenomenon is especially critical in highly loaded functional areas because the metal degenerates where strength is most needed.

The chemical reaction that causes rust begins spontaneously and once established is self-generating. Moisture condensing on a metal surface will slowly dissolve enough base metal to act as an electrolyte. Once started the surface metal becomes microscopically porous and actually absorbs moisture to accelerate pitting.

A pit in an area of high surface stress concentration is disastrous. A typical pit is .020 of an inch deep and will form a root crack under loading. This will degenerate the structure that was intended to be under high loading.

Sealing the metal surface with a smearable tacky coating that is chemically inert will exclude the electrolyte and oxidation.

Bill Van Appledoorn