The most common form of rust is the well-known red-brown coating that forms on iron and steel. The term ‘rust’ is only given to oxidation on iron and iron alloys, such as steel. Rust is the general term for iron-oxide. Other forms of oxidation are the black patina on silver, and the typical green oxidation on copper. Effective removal of rust? Then read on!
The well-known rust on iron forms when iron comes into contact with water and oxygen. Despite the air containing roughly 21% oxygen, iron will not rust on contact with dry air. Rusting, or oxidation, only happens when iron comes into contact with humid air or water. A relative humidity of >50% is enough to start oxidation, above 80% humidity this process is significantly faster.
Dissolved electrolytes (ions/salts) will increase the speed of oxidation. Which explains why rusting of iron is much quicker in salt water and salt environments. Acidic environments or fluids will also exponentially increase the speed of oxidation.
As described, rust is the result of an oxidation reaction between iron, water and oxygen:
Iron + water + oxygen à Hydrated iron (III) oxide
The product of this reaction: hydrated iron (III) oxide, will crystallise and form the typical red/brown flakes. This form of oxidation is very brittle, weak and vulnerable and should be prevented. Additionally, a rusty surface will continue to rust.
Stainless steel contains chrome, which can oxidize, similar to iron. Opposed to rust which is weak and brittle, chrome forms a very strong oxide which leaves a very strong invisible layer on the steel. This layer prevents the iron from rusting.
Rust can be removed in different ways. One way is by grinding or sanding the rust off. This is effective in removing the rust, but does not prevent the underlying rust from oxidizing again..
The most effective method for removing rust is by using chemistry. Rust can be removing using acids. More specifically, and most effective: phosphoric acid. Phosphoric acid reacts with iron (III) oxide to form iron (III) phosphate. The iron (III) phosphate is then easily scrubbed or washed off of the surface.
RUSTREMOVER is a product developed by MAVRO. RUSTREMOVER is based on phosphoric acid, corrosion-inhibitors and other performance enhancing additives. RUSTREMOVER effectively removes rust from any surface and leaves a protective phosphate layer. This phosphate layer on its own provides temporary rust protection along with the corrosion inhibitors. The phosphate layer also acts as a corrosion inhibiting primer. When coated, the phosphate layer will provide improved adhesion and active rust-inhibiting.
Did you know: Cola also contains a considerable amount of phosphoric acid and will also be effective against mild rust. Cola also has a very low pH of roughly 2,7.