THE CORROSION AND POLARIZATION BEHAVIOR OF COPPER IN DOMESTIC WATER IN THE PRESENCE OF CA, MG AND NA-SALTS OF PHYTIC ACID

Phytic acid has been proposed as an inhibitor of copper corrosion in p otable waters. This paper is concerned with the inhibiting action of t he Ca, Mg and Na salt derivatives of phytic acid which have, to date, been little studied. A synthetic domestic water (SDW) (pH = 6.8) conta ining 36.6 mg l(-1) HCO3-, 42.6 mg l(-1) Cl-, 76.8 mg l(-1) SO42- and 100 mg l(-1) NaClO was prepared and the corrosion and polarization beh aviour of copper in solutions containing different levels of the three salts alone was evaluated by weight loss, potentiodynamic and potenti ostatic techniques at 30 degrees C and in some cases at 65 degrees C. Uniform corrosion was found to occur in the SDW and this was inhibited by the Ca and Mg salts. These salts have a limited solubility (approx . 4 x 10(-4) M) and the relative inhibition efficiency of Ca and Mg ph ytate saturated solutions was calculated at 90.1 and 91.0%, respective ly. The Na phytate was completely soluble and promoted the formation o f a passive film. Maximum inhibition (65.3%) was obtained at the 1 x 1 0(-2) M level and this salt, unlike the other two, would not be a suit able candidate for the inhibition of copper corrosion in potable water s. Surface analysis indicated the formation of a Cu phytate film on to p of the copper oxide(s) film.