The corrosion and polarization behaviour of copper in domestic water in the presence of Ca, Mg and Na-Salts of phytic acid

• Published in: Corrosion science Vol. 37; no. 1; pp. 55 - 65
• Main Authors: Notoya, T., Otieno-Alego, V., Schweinsberg, D.P.
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 1995; Elsevier Science
• Subjects: Applied sciences; Corrosion; Corrosion environments; Exact sciences and technology; Metals. Metallurgy; Water corrosion; Plumbing; Polarization diagram; Domestic water; Corrosion rate; Copper; Corrosion protection; Application; Phytic acid; Corrosion inhibitor
• ISSN: 0010-938X; 1879-0496
• DOI: 10.1016/0010-938X(94)00105-F

Phytic acid has been proposed as an inhibitor of copper corrosion in potable waters. This paper is concerned with the inhibiting action of the Ca, Mg and Na salt derivatives of phytic acid which have, to date, been little studied. A synthetic domestic water (SDW) (pH = 6.8) containing 36.6 mg 1 −1 HCO 3 −, 42.6 mg l −1 Cl −1, 76.8 mg l −1 SO 4 2− and 100 mg l −1 NaClO was prepared and the corrosion and polarization behaviour of copper in solutions containing different levels of the three salts alone was evaluated by weight loss, potentiodynamic and potentiostatic techniques at 30 °C and in some cases at 65 °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 × 10 −4 M) and the relative inhibition efficiency of Ca and Mg phytate saturated solutions was calculated at 90.1 and 91.0%, respectively. The Na phytate was completely soluble and promoted the formation of a passive film. Maximum inhibition (65.3%) was obtained at the 1 × 10 −2 M level and this salt, unlike the other two, would not be a suitable candidate for the inhibition of copper corrosion in potable waters. Surface analysis indicated the formation of a Cu phytate film on top of the copper oxide(s) film.