Lithium carbonate and lithium oxalate were incorporated as leachable corrosion inhibitors in model organic coatings for the protection of AA2024-T3. The coated samples were artificially damaged with a scribe. It was found that the lithium-salts are able to leach from the organic coating and form a protective layer in the scribe on AA2024-T3 under neutral salt spray conditions. The present paper shows the first observation and analysis of these corrosion protective layers, generated from lithium-salt loaded organic coatings. The scribed areas were examined by scanning and transmission electron microscopy before and after neutral salt spray exposure (ASTM-B117). The protective layers typically consist of three different layered regions, including a relatively dense layer near the alloy substrate, a porous middle layer and a flake-shaped outer layer, with lithium uniformly distributed throughout all three layers. Scanning electron microscopy and white light interferometry surface roughness measurements demonstrate that the formation of the layer occurs rapidly and, therefore provides an effective inhibition mechanism. Based on the observation of this work, a mechanism is proposed for the formation of these protective layers.

Lithium salts are being investigated as leachable corrosion inhibitor and potential replacement for hexavalent chromium in organic coatings. Model coatings loaded with lithium carbonate or lithium oxalate demonstrated active corrosion inhibition and the formation of a protective layer in a damaged area during neutral salt spray exposure. The present paper provides an abridged overview of the initial studies into this novel inhibitor technology for the active corrosion protection of aluminum alloys. Coating defects were investigated by microscopic techniques before and after exposure to corrosive conditions. Scanning electron microscopy analysis of cross-sections of the coating defect area demonstrated that the protective layer comprises a typical three-layered structure, which included a dense layer near the alloy surface, a porous middle layer, and a flake-shaped out layer. Potentiodynamic polarization measurements obtained with a microcapillary cell positioned in the coating defect area and electrochemical impedance spectroscopy confirmed the corrosion protective properties of these protective layers. The long-term corrosion inhibition of the lithium-based coating technology was tested in industrial coating systems.

The development of anodic films at a constant current density of 10 mA cm⁻² has been studied for Mg-W alloys, containing 0.4 and 1.0 atom % W, in 3 M ammonium hydroxide/0.05 M ammonium phosphate electrolyte at 293 K. The structure, morphology, and composition of the films were determined by X-ray diffraction, scanning electron microscopy, atomic force microscopy, glow discharge optical emission spectroscopy, Rutherford backscattering spectroscopy, and nuclear reaction analysis. During anodizing to about 50 V, a relatively smooth film develops. Cross-sectional atomic force microscopy suggests the film may be finely porous. With an increase in voltage, the film transforms gradually to a coarse, porous morphology due to dielectric breakdown. The transformation coincides with a reduction in slope of the voltage-time response. Significant regions of both types of film morphology coexist during anodizing to 150 V. With further anodizing, a porous film, developed in the presence of sparking above about 270 V, eventually covers all of the macroscopic surface. Magnesium, phosphorus, oxygen, hydrogen, and nitrogen species are present throughout the film thickness at the resolution of the measurements. However, the films are initially free of tungsten species due to enrichment of tungsten in the alloy. The O:Mg atomic ratio is in the range 1.7 to 2.1, reducing with an increase in voltage for films formed up to 220 V, consistent with films composed primarily of hydroxide or oxyhydroxide. The P:O atomic ratio increases with an increase in voltage, starting at about 0.03 for voltages below 50 V and reaching 0.29 at 330 V. The films form at a reduced efficiency, typically about 40-50%. © 2001 The Electrochemical Society. All rights reserved.

An investigation into corrosion inhibition properties of a primer coating containing lithium carbonate as corrosion inhibitive pigment for AA2024 aluminum alloy was conducted. It was found that, during neutral salt spray exposure, a protective film of about 0.2 to 1.5 μm thickness formed within the area where an artificial defect was introduced by scribing through the coating to the base alloy. This film showed a multilayered structure consisting of a relatively compact layer near the alloy substrate, a porous middle layer and a columnar outer layer. The thicknesses of the layers varied, as a consequence of the difference in the local concentration of lithium species leaching from the primer coating. The presence of the film in the scribed area significantly reduced corrosion of the alloy, with little consumption of the metal substrate within the scribed area during neutral salt spray exposure. Furthermore, the presence of the protective film resulted in a significant increase of impedance modulus, measured after the salt spray exposure.