Understanding Rust - What is Rust Corrosion

Rust is the product we get when iron goes through the corrosion process. Iron and steel are not found free in nature. Both are extracted from iron ore in a blast furnace or electro oven.

Large amounts of energy are introduced into the iron ore in the extraction process, when this stored up energy is released, the iron has a tendency to corrode back to its natural form "iron oxide" or RUST. Metals that are found free in nature are stable and are classified as being more noble but even metals found in nature have varying electrical potential.

Gold has a potential of 1.498 v whereas Antimony has a potential of only 0.152v once we add man made metals and Alloys to this a very basic scale of a metals nobility would look some thing like this.

This Saxon gold brooche is over a thousand years old with no signs of corrosion Gold is found free in nature you can pan for it, a completely natural and stable metal its free!

The Iron Hammer Axe ia also over 1000 years old Iron is not found free in nature therefore as soon as it is exposed to natures Air and Water it corrodes and disintegrates back to the very earth it came from.

Iron and steel require a barrier surface protection on all surfaces to stop the natural corrosion process. Hence we can say Gold is more noble( stable) than Iron/Steel.

Automotive Metals Nobility Table

  1. GOLD THE MOST NOBLE
  2. TITANIUM
  3. HIGH GRADE STAINLESS STEEL
  4. BRONZE
  5. 50/50 LEAD TIN SOLDER
  6. COPPER
  7. LOW GRADE STAINLESS STEEL
  8. STEEL & CAST IRON
  9. ALUMINIUM
  10. ZINC
  11. MAGNESIUM

Gold being the most NOBLE / CATHODIC + (positive) Magnesium being the least NOBLE most ANODIC - (negative) The less noble metal will be consumed by the more noble metal when they are connected by an electrolyte (water). For example sacrificial anodes are made of zinc when used to protect steel because the zinc will be sacrificed to corrosion and the steel will stay in tact, this is known as cathodic protection.

There are other less known metals and alloys within this scale but for the sake of clarity these have been omitted.

WARNING ! THINK VERY CAREFULL AT THE CONSTRUCTION STAGE HOW CONNECTION OF DISIMILAR METALS IS GOING TO EFFECT CORROSION. AS SOON AS THEY ARE CONNECTED ELECTROLYTIC CORROSION IS INEVITABLE. THE USE OF ISOLATING NON CONDUCTIVE COATINGS, SEALERS ,ADHESIVES AND FASTENERS WILL PREVENT ELECTROLYTIC CORROSION

STEEL IS A CHARGED BATTERY

The energy trapped in all iron and steel can be compared to a charged battery, it has both anodic + and cathodic - particles within its structure. Iron and steel can set free their accumulated energy in the form of electricity as soon as moisture is present, in the same manner as an electric torch battery when connected to an electric light bulb. When the battery runs down the zinc capsule around the battery is consumed and the liquid electrolyte runs out. Exactly the same thing happens to a piece of steel. Some areas of the steel are consumed or corroded during the release of energy - THE STEEL RUSTS Some areas of steel can be more Cathodic than others and this is particularly the case of corrosion forming within seams and crevices. Correct design and restoration methods can prevent this. Rustbuster have a completely integrated range of products that can ensure corrosion free engineering, from construction through to restoration and routine maintenance.

CORROSION PROTECTION METHODS

THE BARRIER PRINCIPLE

The substrate is isolated from the corrosion causing environment by using a coating which has low permeability to moisture and air. This may be achieved by applying a thick coat of paint or applying a paint having low permeability eg. Epoxy, Polyurethane; or even better applying a thick, low pemeability coating. Rustbuster products that fall into this catagory would be Epoxy Mastic 121

PASSIVATION

Corrosion is retarded or arrested by chemical reactions between rust inhibitive pigments in the coating, and the substrate and/or moisture passing through the paint film. The Rustbuster product that would fall within this catagory will be fe-123 Molecular rust converter

CATHODIC PROTECTION

This is achieved by coating the substrate with a paint containing mettalic pigments- usually zinc (Aluminium in some cases), which are ignoble with respect to the substrate. Cathodic protection may also be achieved by means of metal coatings such as zinc galvanising. The rust buster products that fall into this catagory are Zinc Rich Epoxy-Anode (Zinc) and Epoxy -Mastic 121 (Aluminium In order to work effectively the zinc particles must be held in close contact with themselves and the substrate usually a minimum ST3 cleaned surface or blast cleaned for good electrical contact. When a zinc layer is subject to minor damage eg. a scratch, a corrosion rection will take place which produces zinc salts that self-seal the damaged area. See our surface preparation information page ( click number 3 to your left)

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