Identification and Characterization of Nonchromate Corrosion Inhibitor Synergies Using High-Throughput Methods

The replacement of chromate corrosion inhibitors will require synergistic combinations of materials that can only be identified and characterized through experimentation at the present time. One approach to accelerate the discovery and characterization of materials is through the use of high-throughput screening (HTS) methods. This paper presents three methods developed for the HTS of corrosion inhibitors and their combinations for the aluminum aerospace alloy, AA2024-T3 (UNS A92024). Rapid assays for corrosion determination included direct current (DC) polarization, surface copper assessment, and fluorometric detection of Al³⁺. These methods increased experimental throughput by a factor of more than 1,000. Tests were conducted on single and binary combinations of cerium chloride (CeCl₃), yttrium chloride (YCl₃), lanthanum chloride (LaCl₃), europium chloride (EuCl₃), gadolinium chloride (GdCl₃), neodymium chloride (NdCl₃), sodium metatungstate (NaWO₄-3WO₃), sodium metavanadate (NaVO₃), sodium molybdate (Na₂MoO₄), sodium metasilicate (Na₂SiO₃), potassium phosphate (KH₂PO₄), sodium phosphate (Na₃PO₄), and barium metaborate (BaB₂O₄). Testing was performed at 3.4 mM total inhibitor concentration in 0.6 M sodium chloride (NaCl) at pH 2, 4, 7, 10, and 12. The results from each HTS assay correlated well with 10-day electrochemical impedance target data (R² = 0.80 to 0.90). HTS testing revealed both synergistic and antagonistic pairings of the inhibitors. Synergistic combinations have been identified with corrosion inhibition properties that exceed those of chromate under the conditions of these HTS methods. These methods provide a promising route for the rapid discovery and characterization of effective nonchromate corrosion inhibitors and other electrochemical phenomenon.