We present alkali salts of amino acids as functional, non-toxic, non-hazardous, non-volatile, chemically stable, and cheap alkaline additives for common acidic corrosion inhibitors. The resulting mixtures have been evaluated for Co, Ni, and Cu leaching and were analyzed by chip filter assay, potentiodynamic polarization measurements, electrochemical impedance measurements, and gravimetry for corrosion protection of iron and steel in aqueous environment at slightly alkaline pH. Leaching of Co and Ni was found to depend on the corresponding complex stabilities. Taurine (Tau) as well as aminohexanoic acid (AHX) leads to low leaching of Co and Ni. Particularly AHX is an attractive low leaching additive leading to lower Co and Ni concentrations in solution than currently used amino alcohols. Glu and Tau were found to synergistically interact with several acidic corrosion inhibitors of the carboxylic acid and the phosphonic acid type. Tau had a particularly positive impact on the protective properties of carboxyphosphonic acids. Glu had also a positive effect on the anti-corrosive properties of several acidic corrosion inhibitors and served as an anti-scalant. Alkali salts of Glu and Tau might thus serve as commercially and ecologically attractive substitutes for current alkaline additives to acidic corrosion inhibitors.
Keywords: Amino acids; Co-leaching; Corrosion inhibitors; Electrochemistry; Metalworking fluids; Scale inhibitors.
© 2023. The Author(s).