| The overall goal of this research was to identify and investigate possible replacements of chromate corrosion inhibitive pigments for aluminum aerospace alloys. This research project was divided into two objectives: (1) to develop high throughput screening (HTS) methods that rapidly and quantitatively assess inhibitor and inhibitor mixture efficacy on aluminum alloy 2024-T3 (AA2024-T3) for the purpose of identifying synergies, and (2) to investigate the mechanisms of inhibitor interaction for a selected combination of compounds that demonstrate synergistic or antagonistic behavior.; Thirteen inorganic compounds were selected from a review of the literature as promising candidates for AA2024-T3 inhibition or synergists with other inhibitors. These thirteen compounds, a large number of combinations, and sodium chromate were evaluated at 3.4 mM in 0.6 M NaCl to simulate the harsh conditions in which inhibitive pigments must perform.; Three rapid test methods were developed and used to assess corrosion inhibitor performance on AA2024-T3: (1) the current at a fixed DC potential (100 mV) between two AA2024-T3 wire electrodes (50 parallel cells), (2) the cyclic voltammetric measurement of surface Cu following 24 hour open circuit (OC) exposure (96 parallel cells), and (3) the fluorometric measurement of aluminum ion concentration resulting from 24 hour OC corrosion (96 parallel cells). These methods were utilized to assess inhibitor performance on AA2024-T3 as a function of mixture ratio, pH, and concentration.; A number of binary inhibitor mixtures demonstrated both potent and broad-range synergy as identified by the HTS methods. Two binary mixtures, cerium chloride with sodium metavanadate and lanthanum chloride with sodium molybdate, were selected for more detailed investigation due to their antagonistic and synergistic interaction respectively. Experimental evidence supports the hypothesis that the antagonistic interaction between cerium and metavanadate originates from the reduction of pH and active inhibitor concentrations of the constituent species due to a rapid, homogenous reaction between the constituent inhibitors to form a non-adherent, non-inhibitive precipitate. Formation of La-Mo-containing films through a less rapid, heterogeneous reaction over the matrix and intermetallic particles provided greater areas of protective films than either constituent inhibitor, and was the primary cause of synergy between these two corrosion inhibitors on AA2024-T3. |
