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February 25, 2022
What Causes Rust in Metals
Written by: Sam Steele
Metal corrosion, also known as oxidation, occurs when an ionic chemical reaction meets the presence of oxygen on a metal's surface.
The oxidation process takes place in the air while metal is simultaneously exposed to water or to acids. Scientifically speaking, this is when the iron molecules on steels' surface corrode or rust and transform into iron oxides.
So, what causes rust?
What causes rust on metal
Rust is the result of corrosion caused by oxidation in metal. The oxidation process eats away at the metal and creates visible rust on the metal's surface. The lifespan of an uncoated metal that is susceptible to rust is significantly shorter than one that is coated with a zinc-rich cold galvanizing compound.
Left untreated, rust can fully corrode metal into a dry oxide powder; the result of a chemical reaction in the oxidation process.
Elements that can cause rust and lead to fully corrosive metals:
Cold Galvanizing Compounds
A cold galvanizing compound, or zinc-rich compound, has the characteristics of a paint, but it's not a paint. The biggest difference is the percentage of zinc present in the corrosion prevention coating. Because the percentage of zinc in ZRC is so high and the particles are not encapsulated, the corrosion protection is galvanic, like hot-dip galvanizing.
A cold galvanizing compound is a product that simulates the performance of hot-dip galvanizing. So what's the difference?
- Hot-dip galvanizing needs to be applied in a controlled setting, like a manufacturing plant.
- Cold galvanizing compounds can be applied on-site directly out of a can, similar to paint.
A lesser noble metal will corrode to the more noble. Zinc-rich compounds can be applied by spray or brush (like a paint) to steel. Zinc, being less noble than steel, forms hydroxycarbonate salt when it corrodes that bonds with the existing zinc in the film coating while upholding galvanic protection. This creates an advanced, self-healing film that ensures the metal surface beneath the coating stays protected.
This zinc-rich coating, manufactured with ATSM D520 Type III zinc dust, also known as "Ultra-Low Lead." This super high purity zinc dust has fewer impurities than lead and therefore more metallic zinc metal to sacrificially corrode.
Read more about Cold Galvanizing Compounds in this blog post.
Application of Cold Galvanizing Compounds
Once applied and dried, zinc-rich coatings are designed to perform to the same high-level industry standard of corrosion prevention whether sprayed-on or applied by brush.
Brush-on applications will create a better interface between the product and the protected surface than spray-on ones. Brushing mashes the zinc onto the surface and creates better contact between the zinc and steel.
Cold galvanizing spray can be administered in aerosol form or using a compressor or airless spray techniques. ZRC's Cold Galvanizing Compound in aerosol yields the same superior performance as the brush-on type. ZRC simply adds propellants and other ingredients so it sprays easily and evenly out of an aerosol can. ZRC Worldwide's aerosol application method is low in VOC and yields a consistent dry film thickness not found in low-cost solutions. This does not change the performance of the product.
Dealing with a larger project that requires coating a large surface area? Consider using a compressor to apply a ZRC Cold Galvanizing Compound.
Read more about application types.
Zinc in Action
Zinc applied as a protective top-coat is much easier and more financially beneficial to replace than the metal beneath it should it be exposed to rust. A zinc-rich compound has a significantly longer lifespan than an unprotected, oxidized metal, but it, too, corrodes and will eventually need to be replaced. When that time comes, simply sand or grind the original coating down to remove the zinc hydrocarbonate salts that have formed. Then, apply a new coat of ZRC cold galvanizing compound to keep corrosion at bay.
While the zinc corrodes, the surface it's protecting does not rust.
You will eventually need to repair or replace the zinc-rich compound protecting your metal surface. The self-healing film provides full protection, buying you time before maintenance or repairs are required.
Read more about how zinc combats rust.
There are many products that service the varying needs of the corrosion prevention industry. Imitation is flattering, but the proof is in the paint. ZRC Worldwide created zinc coating technology as a hot-dip alternative to combat corrosion and has been a worldwide leader in the space for almost 70 years.
Whether touching up an existing project or completing a full-sized job from scratch, our team will ensure you get the right product and the correct application method for your needs.