The objective of this work was to study the mechanism of corrosion inhibition by pigments used in coil-coated cladding with focus on chromate substitutes able to provide phosphate and calcium ions. Currently intensive investigations are underway worldwide with the aim of finding substitutes for chromate inhibitors.
Phosphates are one of many possible alternatives.
However under certain conditions, phosphates may also act as cathodic inhibitors. Uhlig et al. 2 O The OH - ions involved in the reaction are derived from the cathodic reduction of oxygen. The film is claimed to be effective by limiting access of dissolved oxygen to the metal surface. Na 3 PO 4 solution as a result of cathodic adsorption of positively charged colloidal particles of calcium and magnesium phosphates.