Quantitative Characterisation of Structure in Nuclear Graphite

这项博士研究的目的是建立可靠的/新颖的方法来量化核石墨内部的关键结构特征。这种定量表征对于支持在不同载荷和温度条件下控制中子辐照引起和/或辅助的核石墨损伤和变形的真实机制是至关重要的。这种基于证据的机械论理解将指导从原子、纳米、微米到宏观的尺度上的性质和结构变化的建模。为实现这一目标，提出了以下研究课题作为博士研究生的主要工作重点：(A)用聚焦离子束显微镜分析气孔和微裂纹结构。这项研究将集中在二维图像的定量分析和重建的三维孔隙/微裂纹层析结构上。将开发先进的图像分析技术和算法，用于不同等级的石墨之间以及同一等级具有不同反应堆/MTR历史的石墨之间的基于量化的比较研究。研究结果将与通过其他研究小组使用的其他技术获得的断层扫描数据进行进一步分析。(B)用拉曼光谱和透射电子显微镜进行晶体结构无序分析。这项研究的目的是建立一种非破坏性的方法，可以定量地绘制无序石墨微晶或石墨烯在核石墨中的变化。这种无序信息预计将与辐照历史有很强的关系，即中子剂量、温度、加载水平和类型以及氧化。(C)石墨的真实织构特征。石墨的织构对石墨物性有很大的影响，并使石墨物性沿不同方向呈不均匀分布。在辐照过程中，特别是在压缩/拉伸加载的帮助下，织构可以进一步演变。这项博士研究将使用各种方法来定量描述核石墨的真实结构。

The aim of this PhD research is to establish reliable/novel approaches to quantify the key structural features inside nuclear graphite. Such quantitative characterisation is essential for underpinning true mechanisms governing neutron irradiation-induced and/or -assisted damage and deformation of nuclear graphite under different loading and temperature conditions. Such evidence-based mechanistic understanding will instruct the modelling of property and structure changes at a scale from atomic, nanometer, micron, up to macro. To achieve the aim, the following research topics are proposed as the main focus of the PhD researcher: (a) Pore and micro-crack structure analysis with focused ion beam microscopy. The research will focus on the quantitative analysis of 2D images and reconstructed 3D pore/micro-crack tomography structure. Advanced image analysis techniques and algorithms will be developed for quantification-based comparative studies among different graphite grades, and those with different reactor/MTR histories for the same grade. The research outcomes will be further analysed with tomography data acquired via other techniques used in other research groups. (b) Crystal structure disordering analysis by Raman and TEM. The objective of this research is to establish a non-destructive method that can quantitatively map the variation of disordered graphite crystallites, or graphene, inside nuclear graphite. Such disordering information is expected to have a strong relationship with irradiation history, i.e. neutron dosage, temperature, loading level and type, and oxidation. (c) True texture characterisation of graphite. Texture of graphite can have strong influence on the physical properties of graphite, and brings the heterogeneity in physical properties along different directions. Texture can be further evolved during irradiation, particularly with help of compression/tension loading. The PhD research will use various methods to quantitatively characterise the true texture of a nuclear graphite.