Electrochemical screening and surface analysis of environmentally friendly corrosion inhibitors for aerospace aluminium alloy

Abstract

For the past few decades, the aerospace industry has been actively looking for measures to tackle the problem of localized corrosion of aluminium alloy 2024-T3. One such measure was the use of hexavalent chromium salts as corrosion inhibitors. However, recent studies have reflected the environmental concerns and health impacts associated with these compounds. Since then, there has been a quest for alternatives that can be used as corrosion inhibitors for AA2024-T3.

This thesis is aimed at studying these compounds by testing their inhibitive properties. Selecting an inhibitor from a set of compounds and recommending the best one is a crucial process. The research focuses on the screening of these inhibitors through various electrochemical techniques such as Potentiodynamic Polarisation(PDP), Linear Polarisation Resistance(LPR), and Electrochemical Impedance Spectroscopy(EIS).

The electrochemical experiments during the first 24-hour exposure of AA2024-T3 to inhibitors exhibited that 2,5-Dimercapto-1,3,4-thiadiazole acts as a corrosion accelerator, while Na-Mercaptoacetate and Mercaptobenzimidazole showed the most inhibitive performance among the tested organic compounds. On monitoring their nature during 24 hours, it was observed that they show stable polarisation resistance values after 6 hours. Among the inorganics, Cerium compounds were seen to have better inhibitive properties than the Lithiumcompounds. Additionally, surface studies such as Fourier Transform Infrared Spectroscopy (FTIR) revealed the presence of thiol/mercaptan and carboxyl groups on samples exposed toNa-Mercaptoacetate. X-ray Photoelectron Spectroscopy (XPS) showed oxides of Cerium on samples exposed to Cerium Nitrate. Finally, the correlations between the inhibition efficiencies calculated from different electrochemical testing methods were illustrated using Pearson’s correlation method.