Chen, B; (2013) X-ray Imaging of Three-dimensional Spatial Structure of Coatings. Doctoral thesis (PhD), UCL (University College London).

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Abstract

Coatings, typically painted films, one of the most important and widely-used surface treatment materials, were selected as the subject of this research project. In this dissertation, detailed three-dimensional (3D) spatial structures of three types of coating specimens: silver epoxy adhesive, iron oxide alkyd paint and aluminium epoxy marine coating were obtained by using different 3D X-ray imaging methods and comparative 3D electron imaging means. The shapes and spatial distributions of particles of the main functional ingredients of all these coating specimens were demonstrated. Specifically, for the aluminium epoxy marine coating, the quantitative analysis of the sizes, volumes, orientations and spatial distributions and correlations of the aluminium flakes in the matrix materials of the coating were carried out. Furthermore, the 3D structures of the aluminium epoxy marine coating samples were used for the finite element simulations of the (ion) percolation properties of the coating film. This potentially provides us with a practical method to engineer the efficacy of coatings by modelling their performances based on the actual structures instead of using assumed model structures. This is a new way to evaluate the performance of materials, and also can be an approach for validating their mechanistic assumptions. It could help to shorten the product research and development lifetime, complementing endurance studies of original specimens. The work presented in the dissertation is the first systematic research of 3D spatial structures of coatings and it could help guide coating researchers how to choose the most suitable 3D investigation method for a specific coating specimen. Through comparative experiments, transmission X-ray microscopy (TXM), ptychographic Xray computed tomography (PXCT), X-ray holo-tomography and serial block-face scanning electron microscopy (SBFSEM) have been verified as effective ways to reveal 3D spatial structures of complex industrial specimens. A comparison among these 3D imaging approaches and their advantages and disadvantages are discussed. The wave-front modulation coherent X-ray diffraction imaging was also implemented. It proved to be a capable method of measuring structures of coating samples and reaches similar resolution as TXM. Developing it into a 3D coherent X-ray imaging methodology with capabilities of obtaining a unique image solution from a single diffraction pattern is left as future work.

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