Alkali salts of amino acids as alkaline additives for neutralization of acidic corrosion inhibitors

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.

Automated summary

We propose alkali salts of amino acids as inexpensive and environmentally friendly additives for acidic corrosion inhibitors. These salts effectively protect iron and steel in slightly alkaline aqueous environments and have low leaching rates of Co and Ni. Taurine and aminohexanoic acid are particularly effective additives, surpassing the performance of current amino alcohols. Glu and Tau synergistically interact with carboxylic acid and phosphonic acid corrosion inhibitors, with Tau exhibiting a positive impact on carboxyphosphonic acids. Glu also enhances the anti-corrosive properties and acts as an anti-scaling agent.