Corrosion is a natural process that converts a refined metal into a more chemically-stable form such as oxide, hydroxide, or sulfide. Corrosion in metals is economically punitive as it damages components and parts thereby calling for frequent replacement of the parts or the whole component depending on severity. Convectional metal corrosion studies mainly considered reactions between metal matrices and anions such as Cl−, SO42−, NO−, CO32− from the environment. These studies largely ignored the effects and contributions of cations such as Na+ on the atmospheric corrosion. This was majorly due to two reasons: first, it is difficult to detect the corrosion products of cations such as NaAlCO3(OH)2 (dawsonite) and second, the element detection methods used in corrosion analysis are limited either to surface detection or have low sensitivity to Na+ element. At present, noteworthy studies have shown that Na+ corrosion products such as dawsonite play an important role in the corrosion process of metals. Unfortunately, detecting Na+ or its corrosion products remains a challenging task.
To address this, researchers from the State Key Laboratory of Photocatalysis on Energy and Environment at School of Mechanical Engineering and Automation from Fuzhou University Dr. Xingchen Chen, Dr. Jie Wang, Dr. Xuewei Ju and Professor Xiangfeng Wang applied the single-shot Laser-induced breakdown spectroscopy (LIBS) in the early atmospheric corrosion study of aluminum samples. Their aim was to carry out an in-depth profiling in the Al corrosion samples. Their work is currently published in the research journal, Applied Surface Science.
In their approach, the research team first resolved Na spectral lines. This was followed by a thorough analysis of both the spectral lines and three-dimensional (3D) crater morphology in order to extract its depth profiles. Lastly, based on the Na+ depth profiling information, the team established an Al atmospheric corrosion model using COMSOL, in which both oxygen reduction and the reduction of ECA were taken into account.
The authors reported that indeed, the Na+ element detected by the Laser-induced breakdown spectroscopy originated from atmospheric corrosion. Further, the team noted that the relationship between the relative content of Na+ element and the corrosion depth satisfied the power law of a traditional corrosion process.
In summary, Fuzhou University scientists successfully demonstrated the application of LIBS and 3D topography to study the depth profiling of Na+ in corroded Al samples. remarkably, the presented simulation results were consistent with the previous experimental data. The team pointed out that the LIBS technique, which detects the depth profiling of Na+ in the atmospheric corrosion, could be utilized as a necessary auxiliary tool to study the corrosion depth and corrosion rate for the early atmospheric corrosion of metals. In a statement to Advances in Engineering, Professor Xiangfeng Wang emphasized that their investigation on Al atmospheric corrosion from the perspective of Na+ element might be beneficial to the atmospheric corrosion research.
Xingchen Chen, Jie Wang, Xuewei Ju, Xiangfeng Wang. The role of Na+ in Al surface corrosion studied by single-shot laser-induced breakdown spectroscopy. Applied Surface Science, volume 501 (2020) 144238