Gravimetric, Electrochemical and Quantum chemical studies of some Naphthalocyanine and Pathalocyanine derivatives as corrosion inhibitors for aluminium in acidic medium

Abstract

The corrosion inhibition behaviour of seven macrocyclic compounds (including phthalocyanines and naphthalocyanines) namely 1,4,8,11,15,18,22,25 -Octabutoxy-29H,31 Hphthalocyanine(Pc 1), 2,3,9,10,16,17,23 ,24-Octakis(octyloxy)-29H,3 1 H-phthalocyanine(Pc2), 2,9,1 6,23-Tetra-tert-butyl-29H,3 1 H-phthalocyanine 29H,3 I H-phthalocyanine(Pc3), 5,9,14,18,23,27,32,3 6-Octabutoxy-2,3-naphthalocyanine(nPc 1), 2,11 ,20,29-Tetra-tert-butyl-2,3-naphthalocyanine(nPc2) and 2,3-naphthalocyanine(nPc3) on the corrosion of aluminium in 1M HC1 was studied by means of weight loss, electrochemical, quantum chemical and quantitative structure activity relationship(QSAR) techniques. The inhibition efficiencies and corrosion rates were evaluated at temperatures ranging from 30°C - 70°C. The results suggest that inhibition efficiencies are relatively low but increased on the addition of potassium iodide (KI) due to synergistic effect. Langmuir isotherm agrees well with the experimental data. The individual quantum chemical parameters and combined ones (in a QSAR study) suggest strong interactions between the inhibitor and the metal surface. The results also point to the fact that 1,4,8,11,15,1 8,22,25-Octabutoxy-29H,31 H-phthalocyanine and 5,9,14,18,23,27,32,3 6-Octabutoxy-2,3-naphthalocyanine have the highest tendency to donate electrons to an electron poor species. The results are indicative of the possible role of macrocyclic compounds as corrosion inhibitors for Al surface.