ABSTRACT
This article presents the synthesis of a novel hybrid sol-gel coating and its functionalization with various waste material additives. The unmodified and modified hybrid coatings were deposited on mild steel (MS) substrates, and their anticorrosion performance in a 3.5 wt.% sodium chloride corrosive environment was assessed using potentiodynamic polarization and impedance electrochemical techniques. The Fourier Transformed Infrared Spectrometry (FTIR) spectral, thermal, surface-roughness, scratch-resistance, and contact-angle characterizations were also conducted on the fabricated coatings. Electrochemical techniques proved that the coating sample loaded with the limestone additive showed the best anticorrosion behavior in the saline environment after 4 weeks of exposure. Moreover, the obtained morphological analysis data indicated better surface integrity and cross-link density for this sample compared to other waste-modified coatings. Conversely, the tire rubber and activated carbon additives showed a severe negative impact on the thermal, mechanical, and barrier properties of the parent coating, which can be attributed to the high porosity and less integrated natures of these modified coating formulations proved by their morphological images. Still, all loaded waste additives to the hybrid coating have enhanced its adhesion to the steel surface, as indicated by scratch resistance testing. Overall, the results of the present study show the need for maintaining a balance between the economic value of the modification methodology of hybrid coatings and the type of the loaded waste material additive.
ABSTRACT
In this work, friction stir processing using a pinless tool with a featured shoulder was performed to alter the surface properties of Al 6061-O, focusing on the effect of tool traverse speed on surface properties, i.e., microstructure, hardness, and corrosion resistance. All processed samples showed refinement in grain size, microhardness, and corrosion resistance compared to the base material. Increasing tool-traverse speed marginally refined the microstructure, but produced a significant reduction in microhardness. Electrochemical impedance spectroscopy, linear polarization resistance, and potentiodynamic polarization were used to evaluate the effect of the processing conditions on corrosion behavior in a saline environment. All corrosion test results are found to agree and were supported with pictures of corroded samples captured using a field emission scanning electron microscope. A remarkable reduction in the corrosion rate was obtained with increasing traverse speed. At the highest traverse speed, the corrosion current density dropped by approximately 600 times when compared with that of the base alloy according to potentiodynamic polarization results. This is mainly due to the grain refinement produced by the friction stir process.
ABSTRACT
In this study, a novel hybrid sol-gel coating on AA3003 substrate was developed and the effects of various waste material additives on the reinforcement of the sol-gel coating and the anticorrosion properties in the saline medium were investigated. Egg shell, crumb rubber, activated carbon obtained for pyrolysis of waste rubber tire, waste rubber tire, cement kiln dust, and ST100 additives were tested as reinforcement materials. The AFM characterization results of the coating formulations on AA3003 alloy revealed enhanced roughness values for the modified coatings as compared to the base coating. Similarly, no significant changes were detected in the Fourier transform infrared spectroscopy (FTIR) absorption peaks of the hybrid polymeric material upon loading it with the waste additives, while slight changes in the hydrophobic properties of the final modified coatings were observed as a result of the modification process. Electrochemical impedance spectroscopy (EIS) results revealed that the hybrid sol-gel coating had a promising potential for the protection of the AA3003 substrate against corrosion in the saline medium. However, the loaded additives negatively affected the corrosion resistance properties of the parent hybrid sol-gel coating. For instance, the egg shell additive had the least negative effect on the barrier properties, whereas the cured coating layer of the sample loaded with cement and clay additives showed some disintegration, inhomogeneity, and low barrier properties on the metal surface.
