A chemiometric approach for phosphate inhibition of copper corrosion in aqueous media

Abstract

The inhibition of copper corrosion in aqueous media by inorganic phosphates has been studied using a chemiometric approach (experimental and simplex designs). To achieve the objective, four steps were recognized. When submitted to aqueous aggressive media, the anion nature and its concentration were the important variables for the explanation of the mass loss variation. The most corrosive experimental conditions were: anion: chloride (Cl⁻); concentration: [Cl⁻] = 1 mol/l; exposure time: 24 h. In the second step, two inorganic phosphates, Na₃PO₄ and Na₅P₃O₁₀, are tested as copper corrosion inhibitors when the material is submitted to the severe conditions. The chemical structure was found to be the most influent factor. However, %IE varies between 25% and 56%. Then, we recognized a passivating treatment by submitting copper to inhibitor solution before immersion in the aggressive medium. Three parameters were studied: inhibitor structure, chemical concentration and passivation time (tp). We concluded that tp is the most influent experimental factor. The best passivating conditions are: inhibitor: Na₅P₃O₁₀; inhibitor concentration: [Inhibiteur] = 10⁻² mol/l and passivation time: 3 h. The inhibition efficiency was 89%. To increase %IE, a simplex design was also performed starting by the above obtained conditions and using the polyphosphate (Na₅P₃O₁₀) as inhibitor. The optimum experimental conditions for phosphate inhibition of copper corrosion in aqueous media are: inhibitor: Na₅P₃O₁₀, [Na₅P₃O₁₀] = 0.017 mol/l and passivation time tp = 2.17 h. Under these conditions an inhibition efficiency of 98% was reached.