White rust is a localized corrosive attack on the zinc surface, appearing as a chalky substance as deposits. This is rapid corrosion and usually occurs when zinc is exposed to oxygen and hydrogen. White rust is also called storage white stain.
White rust is often found on new galvanized steel products. These deposits degrade the steel’s appearance and gradually consume the entire zinc layer. White rust is essentially zinc hydroxide and is formed by the chemical reaction of zinc with air and water when wet.
Table of Contents
Causes of White Rust
White rust develops on freshly galvanized steel when exposed to water or hydrogen dioxide. During these first few days, the zinc layer is most susceptible to white rust as the steel is attacked.
However, old zinc surfaces can also be corroded by white rust if the surface is exposed to high pH, highly conductive water, or if the old surface is washed aggressively.
When galvanized steel is stored for future use, without proper air circulation, moisture (rain, dew, condensation) can easily become trapped between individual items, leading to the formation of white rust there is. Basically, the following factors contribute most to the formation of white rust:
- Wet Climate
- Poor Air circulation
- Storage method (humid storage location)
How to Prevent White Rust?
There are several ways to prevent white rust. Some of these methods are:
- Allow the zinc to form a stable oxide before exposure to moisture.
- Avoid contact with water (outdoor products should be covered with a breathable waterproof cover)
- Eliminates the possibility of condensation (can provide water repellent or barrier coatings)
- Use of passivating chemicals or oils to prevent oxidation of zinc.
- Store galvanized steel products in a dry, well-ventilated area.
- Do not expose cold zinc material to warm environment
Closing Thought
The formation of white rust can seriously damage optics. Furthermore, the coating becomes unusable and the base product (steel) becomes susceptible to corrosive attack again. Therefore, white rust is undesirable and should be checked or removed.