Full metadata record
| DC Field | Value | Language |
|---|---|---|
| dc.contributor | Department of Aeronautical and Aviation Engineering | en_US |
| dc.contributor.advisor | Zou, Fangxin (AAE) | en_US |
| dc.contributor.advisor | Su, Zhongqing (ME) | en_US |
| dc.creator | Chen, Yunda | - |
| dc.identifier.uri | https://theses.lib.polyu.edu.hk/handle/200/13116 | - |
| dc.language | English | en_US |
| dc.publisher | Hong Kong Polytechnic University | en_US |
| dc.rights | All rights reserved | en_US |
| dc.title | High-precision in-situ ultrasound-based platforms for imaging localized corrosion-induced morphological changes and evaluating structural evolution of corrosion product layers | en_US |
| dcterms.abstract | Steels, as widely applied materials, often serve in corrosive environments, such as marine, petroleum, and high-humidity atmospheric conditions. It leads to the dissolution of steel and further results in structural failures, environmental contaminations, and economic loss. A comprehensive understanding of the dynamic progress of steel corrosion is crucial for proposing more sustainable strategies for corrosion control and prevention. The dissolution of steel during corrosion, directly correlated with structural strength, is one of the primary focuses of research in this field. In situ microscopic techniques and electrochemical techniques have been developed to characterize morphological information of substrate. However, microscopic techniques that can directly profile the morphology of substrate typically lack the ability to penetrate corrosion product layers formed naturally during corrosion. This makes them inapplicable in many practical corrosion systems. Indirect electrochemical techniques usually rely on Faraday’s law to convert measured corrosion current to the amount of dissolved metal, while the non-Faradaric current released by charge and discharge of capacitive components in the system would affect the accuracy of electrochemical reconstruction. Besides the morphological change of corrosion substrates, the substantial formation of corrosion product layers, which could significantly affect corrosion progress by insulating metal surfaces from corrosive environments, has also been widely discussed. Currently, both the chemical composition and electrochemical response of corrosion product layers can be obtained in a real-time and non-destructive manner. However, acquiring the structural information of corrosion product layers is usually destructive and ex-situ. In this case, continuously tracking the structure change of the same corrosion product layer would be infeasible. | en_US |
| dcterms.abstract | Aiming to break through the abovementioned limitations of conventional corrosion research techniques applied for steel corrosion study, in this thesis, relying on ultrasound propagating inside corrosion substrates, three in-situ and non-destructive ultrasound-based platforms are developed for imaging corrosion substrates during corrosion or evaluating the structure change of corrosion product layers attached to the corrosion surface. The first platform consists of an ultrasonic transducer array, and each array element will continuously track the thickness change of an individual micro-section of the corrosion substrate. By fusing the thickness information obtained by the whole array, the real-time morphology of the corrosion surface can be reconstructed. This platform provides a customizable lateral resolution, an ultra-high axial resolution of 100 nm, and an experimentally proven measurement accuracy. Following this work, a technique that can generate and precisely control moveable ultrasound on a permanently installed piezoelectric transducer is introduced. Based on this technique, a high-resolution and high-precision imaging platform without using higher-frequency ultrasound is proposed. Through an inversion algorithm, the finest lateral resolution can be as small as scanning displacement. The actual platform established reaches 1 mm × 1 mm lateral resolution by only using 2 MHz ultrasonic waves. Its axial resolution is still as high as a sub-micron level, and accuracy is validated experimentally. The focus of the third platform is to track the structural evolution of corrosion product layers non-intrusively. To construct the monitoring setup, two piezoelectric transducers that can generate ultrasonic waves vibrating in different directions, i.e., longitudinal and shear, are installed at the non-working surface of a substrate. During experiments, they will be excited alternately to generate the ultrasonic waves propagating along the thickness direction of the substrate and sense the reflected ultrasonic waveforms from the corrosion surface. The performance of the proposed technique is first validated by monitoring zinc electroplating and natural evaporation of electrolyte thin film containing synthetic Fe(OH)2. Then, the processes of corrosion product layers formed by the wet-dry cycle corrosion on different steels and electrolytes are investigated based on the proposed technique, SEM, optical surface profiler, optical microscope, and electrochemical evaluation. | en_US |
| dcterms.extent | viii, 172 pages : color illustrations | en_US |
| dcterms.isPartOf | PolyU Electronic Theses | en_US |
| dcterms.issued | 2024 | en_US |
| dcterms.educationalLevel | Ph.D. | en_US |
| dcterms.educationalLevel | All Doctorate | en_US |
| dcterms.LCSH | Steel -- Corrosion | en_US |
| dcterms.LCSH | Nondestructive testing | en_US |
| dcterms.LCSH | Ultrasonic testing | en_US |
| dcterms.LCSH | Hong Kong Polytechnic University -- Dissertations | en_US |
| dcterms.accessRights | open access | en_US |
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