Establish models for predicting physical properties of a nuclear graphite based on its experimentally observed microstructure

到目前为止，还没有一个完整的模型可以根据实验观察到的微观结构来预测核石墨的物理性质。另一方面，对于大多数关键的金属和陶瓷材料，物理性能和微观结构之间的相关性已经相当好地建立起来，使组件设计和寿命管理更容易，更耗时。然而，从事核石墨工作的工程师/科学家仍然依赖于极其昂贵和非常耗时的实验工作，通过材料测试反应堆（MTR）中的加速中子辐照来获得最需要的物理特性。这种情况的关键原因之一是核石墨的微观结构非常复杂，特别是从纳米到微米的尺寸尺度。在过去的几年里，拉夫堡核石墨集团（LNGG）一直在研究核石墨的微观结构和相关的结构特征。其中，“疯狂铺路”作为关键的基本结构单元已被实验和理论证明。这些单元是核石墨的主要组成部分，并且最近已经发表了结果。基于建模的进展和初步尝试，因此我们提出了这项研究，旨在实现这一目标的3年博士生研究。a）根据实验观察到的微观结构建立模型我们认为“疯狂铺路”应该是核石墨的基本组成部分。这项任务的研究将通过实验确定这种构建块如何在合成石墨中的填料和粘合剂内在3D维度上延伸，包括球形QI颗粒和填料的内部关键特征。HRTEM/STEM将用于说明从石墨中特别感兴趣的区域制成的样品的疯狂铺路结构与FIB显微镜。通过UNIGRAF的研究，该方法已经相当完善地建立起来，预计一位博士研究员将从项目一开始就掌握该方法。同时，来自这些区域的拉曼光谱数据将通过HRTEM/STEM的测量进行整理，旨在建立一种有效且非破坏性的工具来量化疯狂的铺路结构。将测试来自拉曼光谱学的测量结果是否可用作预测物理性质的建模输入。B）开发适当的建模工具包，以预测基于这些模型的物理特性，我们将使用基于从头算和经典技术相结合的原子建模来研究预测工具。这项研究还将使用内部开发的计算机代码和模型来调查通常超出这些方法应用范围的扩展时间尺度。到目前为止，拉夫堡的研究团队有2名博士和2名RA研究人员，他们正在研究不同的原子模型。这位博士研究员将成为团队的一员，但明确专注于预测属性。建模将从简单的“疯狂铺路”结构开始，并逐渐进入基于任务a）的测量的由“疯狂铺路”构建块构建的更复杂的结构。该预测将能够扩展到纳米/微米尺度测量可能的几何尺寸。c）建模预测的验证由于石墨结构的复杂性，使用常规物理性质测量来直接验证基于原子建模的工具的预测可能太具有挑战性。然而，如果可以在纳米或亚微米水平上进行性能测量，则可以验证这种建模预测。因此，在本研究中，我们将直接测量电子显微镜内的关键物理特性。我们将首先集中在测量热膨胀系数的加热阶段安装在TEM与试样尺寸的尺寸范围从纳米到亚微米。这些样品

Until now, there is no complete model available to predict physical properties of nuclear graphite based on experimentally observed microstructure. On the other hand, for most key metallic and ceramic materials, the correlations between physical properties and microstructure have been reasonably well established, making component design and lifetime management much easier and less time-consuming. Engineers/scientists working on nuclear graphite, however, are still relying on extremely expensive and very time-consuming experimental work to acquire most needed physical properties through accelerated neutron irradiation in a material testing reactor (MTR). One of the key reasons for such a scenario is the incredibly complicated microstructure of nuclear graphite, particularly across dimension scale from nano-meter to micro-meter. Over the past several years, the Loughborough Nuclear Graphite Group (LNGG) has been investigating the microstructure and related structural characteristics of nuclear graphite. Among the outcomes, "crazy paving" has been experimentally and theoretically evidenced as the key fundamental structural units. Such units are the primary building blocks for a nuclear graphite, and the results have been published recently.Based on the progress and preliminary trial in modelling, we hence propose this research for a 3 year PhD studentship aiming to achieve the goal. a) Establish models based on experimentally observed microstructure We believe "crazy paving" should be the basic building block in nuclear graphite. Research in this task will experimentally establish how such building blocks extended in 3D dimension inside fillers and binders in synthetic graphite, including inside key characteristic features as spherical QI particles and fillers. HRTEM/STEM will be used to illustrate the crazy paving structure of samples made from specifically interested regions in graphite with FIB microscopy. The methodology has been reasonably well established through research in UNIGRAF, and a PhD researcher is expected to get hands on from the start of the project. At the same time, Raman spectroscopy data from these regions will be collated by the measurements from HRTEM/STEM, aiming to establish an efficient and non-destructive tool to quantify the crazy paving structure. Measurements from Raman spectroscopy will be tested if they can be used as modelling inputs to predict physical properties. b) Develop appropriate modelling tool kits to predict physical properties based on these models we will use atomistic modelling based on a combination of ab initio and classical techniques to investigate prediction tools. The research will also use in-house developed computer code and models to investigate extended time scales normally outside the range of application of these methods. By now, the Loughborough research team has 2 PhD and 2 RA researchers who are working on different atomistic modelling. This PhD researcher will be part of the team but with a clear focus on predicting properties. The modelling will start from simple "crazy paving" structure, and gradually move into more complicated structure built up from "crazy paving" building blocks based on measurements from task a). The prediction will be able to extend to a geometric dimension that nano/micro-scale measurements can be possible. c) Validation of modelling predictionDue to the complexity of graphite structure, it might be too challenge by using the routine physical property measurements to directly validate predictions from tools based on atomistic modelling. However, if property measurement can be done at nanometer or submicron levels, such modelling prediction can be validated. Hence, in this research, we will directly measure key physical properties inside electronic microscopes. We will first focus on measurement of CTE on a heating stage installed in TEM with specimen size dimensions ranging from nanometers to sub-microns. These samples