| WANG Luntao,WANG Huiru.Application of Atomic Force Microscopy in Organic Corrosion Inhibitor Research[J],53(2):28-48 |
| Application of Atomic Force Microscopy in Organic Corrosion Inhibitor Research |
| Received:December 26, 2023 Revised:January 03, 2024 |
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| DOI：10.16490/j.cnki.issn.1001-3660.2024.02.003 |
| KeyWord:atomic force microscopy surface technology organic corrosion inhibitors surfactants contact mode tapping mode |
| Author | Institution |
| WANG Luntao |
Ohio University, Ohio State, Athens 45701, US |
| WANG Huiru |
Ohio University, Ohio State, Athens 45701, US |
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| Abstract: |
| Organic corrosion inhibitors have advantages such as low toxicity and cost-effectiveness. They demonstrate excellent corrosion inhibition efficiency at low injection doses and are used extensively to protect alloy materials from corrosion in petrochemical (carbon steel), electronic (copper), automotive, maritime and aerospace industries (aluminum). The study on the mechanism of organic corrosion inhibitors helps improve and optimize the design of inhibitors and the adjustment of their molecular structure or formulation can enhance their anti-corrosion performance. The existing electrochemical testing techniques have been widely applied in the field of organic corrosion inhibitors. While these methods can only offer information about the average kinetic of interfacial electrochemical reactions, they do not directly decipher the adsorption mechanisms of corrosion inhibitors. With the microscopic and systematic development in the study of metal corrosion and corrosion inhibitors, electrochemical analysis methods are progressively integrated with other analytical techniques (such as scanning electron microscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, etc.), enabling an in-depth analysis of the mechanisms behind corrosion inhibitor action. Among these analytical techniques, Atomic Force Microscopy (AFM) has played a significant role in the direct study of organic corrosion inhibitors at the metal/solution interface due to its high spatial resolution imaging capabilities and fewer limitations concerning working environments and sample properties. In the field of organic corrosion inhibitor research for metals and alloys, the most widely used AFM technique is the morphology characterization and the analysis of surface roughness in contact mode, and the aim is to assess the corrosion inhibition effectiveness of organic corrosion inhibitors by evaluating the corrosion level of the materials. This technique provides high-resolution and intuitive microscale corrosion morphology, coupled with electrochemical and surface composition analysis, which is highly beneficial for studying corrosion efficiency and mechanisms. Additionally, this operation mode is simple, leading to the majority of AFM work in corrosion inhibitor research being conducted with this technique. However, the limitation of AFM contact mode lies in its inability to deeply investigate the adsorption behavior of corrosion inhibitor films. Due to the lateral force inherent in AFM contact mode, there is a possibility for surface damage during the study of soft materials like organic corrosion inhibitor films. To address this, the tapping mode of AFM is introduced. Initially utilized for studying the adsorption and desorption of surface-active agent substances on hydrophilic or hydrophobic inert surfaces, this tapping mode has gradually extended to the study of organic corrosion inhibitors in recent years. Particularly, the phase imaging technique in this mode directly acquires the adsorption structure of corrosion inhibitor molecules, thus significantly facilitating in-situ studies of organic corrosion inhibitor films. However, its limitation lies in the restricted scanning and frequency modulation speed in corrosion inhibitor solutions, making it challenging to monitor the adsorption kinetics and dynamic adsorption-desorption processes. Currently, some developing technologies, such as peak force tapping mode, aim to enhance the existing tapping mode for better suitability in studying soft materials. Apart from the fundamental contact and tapping modes, AFM has been combined with other analytical techniques, developing multifunctional analysis methods for organic corrosion inhibitor research. For instance, Electrochemical Atomic Force Microscopy (EC-AFM) not only records local corrosion morphology, but also applies voltage on surface for polarization modification or synchronizes electrochemical tests to gather corrosion electrochemical process information. Additionally, AFM force-distance curve functionality and lateral force microscopy enable simultaneous acquisition of surface microstructure and mechanical properties of organic adsorption films, significantly aiding in evaluating inhibitor effects and studying corrosion mechanisms. These comprehensive analysis techniques can be widely applied in corrosion inhibition on materials like gold or stainless steel, while their use on carbon steel is limited due to the rapid corrosion rate of carbon steel surfaces, surpassing the scanning rate of AFM probes, making these finer mechanical measurements or surface electrochemical modifications challenging. In the future, AFM will evolve towards multifunctionality, high sensitivity, high speed, and efficiency. Its application in the field of organic corrosion inhibitor research will further integrate with other advanced surface micro-area analysis technologies, interpreting the structure of organic corrosion inhibitors/metal interfaces and corrosion mechanisms from various perspectives such as surface chemistry, electrochemistry, mechanics, physics, and materials science. The continuous improvement of AFM technique will facilitate deeper studies of in-situ dynamic corrosion processes and drive research in the field of organic corrosion inhibitors. |
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