Zinc and polyphosphates as corrosion inhibitors for zinc in near neutral waters

The corrosion and corrosion inhibition of commercial purity zinc, in the presence and absence of polyphosphate, was examined by electrochemical impedance spectroscopy (EIS) and by cyclic voltammetry using artificial waters as electrolytes. The anodic dissolution reaction exhibited mixed kinetics which changed to diffusion control when calcium ions were removed. The effect of calcium to polyphosphate ratio on the corrosion rate of zinc was studied to determine the composition which gives the optimum protection. A recirculating system that utilises galvanised tubing was used to test optimum concentrations found by EIS with good results.