Definition - What does Back Ionization mean?
Back ionization is the excessive deposition of charged powder particles, preventing further powder from being deposited on the substrate. This results in improper surface coating.
This phenomenon causes coatings to have high porosity and improper bonding, leading to a coating that is not suitable for corrosion protection.
Back ionization is also known as starring or starburst effect.
Corrosionpedia explains Back Ionization
When charged powder coating is applied to a metal surface, the thickness of powder coating increases. Because of this, a cumulative charge will be produced by powder particles on the coating as coating's thickness increases. As the coating thickness increases, the strength of the electric field becomes sufficient to ionize air trapped between powder particles.
The ionization of air generates a great number of positive ions. These positive charges try to escape from the coating and attract the negative charge of the coating particles. This creates an uneven coating surface. This causes an "orange peel" texture on the powder's surface. The phenomenon is more typical when applying a second coat on a part, but can occur when applying the first coat.
How to avoid back ionization:
- Lower voltage settings
- Optimizing distance between the gun and coating surface
- Ion collector use: A grounding ring or grounding source of power