Abstract
Materials corrosion is a natural and ubiquitous interfacial process, but is essential to numerous industrial processes. Progress in industrial and material innovations is also marked by developments in search of new solutions to designing materials with better anticorrosion activity and longer service lifetime. With increasing engineering implementation and progress in materials, and manufacturing, there is a revival in this classical area and many important progresses emerge. In particular, three key design components that underlie the construction of an ideal protective coating, i.e., the functional barrier at the coating surface, the transport control of corrosive substances inside the coating, as well as interfacial bonding between the passive coating and the substrate were inspired from nature. Moreover, recent blossoming in biomimetics has provided remarkable inspirations to design new artificial, passive anticorrosion coatings or natural inhibitors that are environmentally benign and functional versatile. The aim of my thesis is to advance our fundamental understanding of repellent function in nature, imitate the exquisite function and composition to attain superior anticorrosion functions, even go beyond nature in some special cases.First, we revealed the sensitive and responsive control of ions and liquid transport within mangrove. As one typical plant living along marine coastline in tropical or subtropical regions, mangrove secretes salt by salt gland and deposits salt crystals on the leaf surface. In addition to the salt resistant of salt gland, the rich presence of tannin in mangrove bark also play an important role in protecting mangrove from the harsh surroundings. In particular, the salt repellent ability of mangrove could provide important insights for the design of passive coatings for anticorrosion. Additionally, mangrove tannin was found with antifouling ability for mangrove bark and the extracted mangrove tannin could be applied as antibacterial reagent. This extents the protective strategy into a broader spectrum of applications.
Second, inspired by salt-secreting ability of mangrove salt gland, we proposed a design of bioinspired, anticorrosion coating based on doping ion-selective resins and constructing surface structures. In addition to the doped ion-selective resins blocking the transport of both Na+ and Cl-, the top hydrophobic layer also plays an important role in resisting the salt solution. Thus, the Mangrove-inspired coating system have top-down protective ability and the coating system could exhibit significantly improved anticorrosion properties, more than three orders of magnitude decrease in corrosion current density compared with the control group (epoxy varnish).
Third, we further explore the protective ability of mangrove tannin for Q235 steel in neutral and acid salt solution. We found that mangrove tannin could form an adsorption layer replacing water at the metal–solution interface. However, the adsorbed mangrove tannin cannot take actions as a protective layer to Q235 steel and accelerate the anodic reactions in neutral 3.5wt%NaCl solution. While the adsorption of mangrove tannin could delay the anodic and cathodic corrosion processes of Q235 steel in acid 3.5wt%NaCl solution. Although mangrove tannin could provide protection with nearly 64% anticorrosion efficiency, it cannot be applied as effective inhibitor for Q235 steel in acid 3.5 wt% NaCl solution.
In summary, we systemically investigated the anticorrosion strategy on mangrove. Getting inspiration from salt-secreting ability, a novel top-down protective coating was firstly proposed to protect metals from corrosion. Furthermore, we explore the antifouling and anticorrosion ability of mangrove tannin, which have much better anticorrosion performance in acid surroundings. Moreover, mangrove tannin could provide important insights and reference for exploring natural environmental benign inhibitor. Above all, we believe that our work on the mangrove inspired anticorrosion strategy will yield important insights to the development of anticorrosion strategy and even more spur a wide range of applications.
| Date of Award | 8 Jun 2021 |
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| Original language | English |
| Awarding Institution |
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| Supervisor | Zuankai WANG (Supervisor) |