The action mechanism of ethylenediamine, tetramethylethylenediamine, and disodium ethylenediaminetetraacetic acid (EDTA-2Na) as corrosion inhibitors for aluminum radiators has been clarified, and the scientific laws between functional groups and corrosion inhibition kinetics have been elucidated. EDTA-2Na has the highest corrosion inhibition efficiency for forming the stable protective layer from the Al-O/N chelating bond with Al through its carboxymethyl group.

Abstract

The use of ethylenediamine-based compounds, including ethylenediamine (EDA), tetramethylethylenediamine (TMEDA), and disodium ethylenediaminetetraacetate (EDTA-2Na), as corrosion inhibitors for aluminum radiators in high-voltage direct current (HVDC) converter valve systems is investigated. The results of the electrochemical analysis demonstrate that EDA spontaneously adsorbs on aluminum surfaces through N–Al coordination, resulting in the formation of a protective layer that achieves a 97.28% corrosion inhibition rate. The electron-donating effect of methyl and carboxymethyl groups increases the electron cloud density of N, which facilitates their electrophilic reaction with Al. The carboxymethyl groups of EDTA-2Na facilitate chelate bonding via simultaneous Al-O/N coordination, resulting in the formation of stable complexes that achieve 99.09% inhibition efficiency. In contrast, the steric hindrance of the methyl group attached to the N atom of TMEDA weakens the adsorption between N and Al, lowering the inhibition efficiency to 96.10%. These molecular-level insights establish definitive structure‒activity relationships, providing scientific guidance for optimizing HVDC coolant formulations through strategic N-functionalization of ethylenediamine scaffolds.