The effect of sodium orthophosphate on the protective characteristics of the surface layers are studied on brass in contact with moderately hard, highly carbonated and chloride rich simulated drinkable water. The optimal inhibitor concentration is evaluated from the composition, thickness and pitting resistance of the surface film. This layer is mainly composed by zinc(II) oxide–hydroxide and cuprous oxide. By adding PO43−, the film quality improves, attributed to the incorporation of CuO or Zn(II) compounds. The changes are evident with 5 mg l−1 P, and between 10 and 20 mg l−1 P no significant differences are observed.
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