Contrary to what is beleived, passivation in phosphate coating lines is not for corrosion protection with itself. Passivation is effective when made prior to paintings. It improves adhesion of paint particles and prepares the surface for following applications to have enhenced corrosion protection.
Passivation treatment eliminates unwanted ionic elements which is coming with water rinsing or after zinc/iron phosphate coatings. These type of water hardening ions have poteintial of producing salts under paint film which can cause blistering or tear of paintings. For all these reasons, use of passivation chemicals improves corrosion protection of painted, especially, powder coated metal parts.
Chromium passivation treatment is used under conditons of % 0,2 – 0,3 chemical concentration and at ambient temperatures. The treatment solution includes hexavalent chromium ions, hence it must be converted to trivalent chromium while discharging.
SOLVER CHEM