Zinc Gluconate as an Inhibitor of the Corrosion of Copper and Zinc in Sea Water

Abstract

The efficiency of zinc gluconate (ZnGl) as an inhibitor of the corrosion of copper and zinc in natural sea water was studied by means of weight loss tests, potentiostatic polarisation and X-ray diffractometry.

It was shown that, in naturally aerated conditions, up to 60% inhibition of copper corrosion is achieved with ZnGl concentrations ranging from 6.10⁻⁴ to 8.10⁻³ mol/l, and that this efficiency increases up to 70% as the period of immersion is increased; in fully aerated conditions, and with ZnGl concentrations ranging from 4.10⁻⁴ to 10⁻² mol/l, the inhibitive efficiency reaches 95%.

It was further observed that the Zn²⁺−CH₂OH(CHOH)₄COO⁻ system is an inhibitor with synergistic properties: maximum inhibition of copper corrosion (90%) is achieved at a Zn²⁺/CH²OH(CHOH)₄COO⁻ molar ratio of 3:2. The mechanism of action of ZnGl on copper ispurely cathodic.The maximum percentage inhibition obtained on zinc was 70% for ZnGl concentrations ranging from 10⁻³ to 4.10⁻³ mol/l. Acceleration of corrosion was, however, observed at ZnGl concentrations below 8.10⁻⁴ mol/l. Inhibition also tends to decrease when the immersion period is increased. The mechanism of action of ZnGl for zinc is also cathodic.