Rana Dhan-Sham B K, Solvas Eugenio Zapatas, Lee William E, Farnan Ian
Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge, CB2 3EQ, UK.
Centre for Nuclear Engineering, Department of Materials, Imperial College London, London, SW7 2AZ, UK.
Sci Rep. 2020 Feb 20;10(1):3096. doi: 10.1038/s41598-020-59698-6.
ZrC (sub-stoichiometric zirconium carbide), a group IV transition metal carbide, is being considered for various high temperature applications. Departure from stoichiometry changes the thermo-physical response of the material. Reported thermo-physical properties exhibit, in some cases, a degree of scatter with one likely contributor to this being the uncertainty in the C/Zr ratio of the samples produced. Conventional, methods for assigning C/Zr to samples are determined either by nominal stochiometric ratios or combustion carbon analysis. In this study, a range of stoichiometries of hot-pressed ZrC were examined by SEM, XRD, Raman spectroscopy and static C NMR spectroscopy and used as a basis to correct the C/Zr. Graphite, amorphous, and ZrC carbon signatures are observed in the C NMR spectra of samples and are determined to vary in intensity with sintering temperature and stoichiometry. In this study a method is outlined to quantify the stoichiometry of ZrC and free carbon phases, providing an improvement over the sole use and reliance of widely adopted bulk carbon combustion analysis. We report significantly lower C/Zr values determined by C NMR analysis compared with carbon analyser and nominal methods. Furthermore, the location of carbon disassociated from the ZrC structure is analysed using SEM and Raman spectroscopy.
ZrC（亚化学计量碳化锆），一种IV族过渡金属碳化物，正被考虑用于各种高温应用。偏离化学计量会改变材料的热物理响应。在某些情况下，所报道的热物理性质呈现出一定程度的分散性，造成这种情况的一个可能原因是所制备样品的C/Zr比存在不确定性。传统的确定样品C/Zr的方法要么是通过名义化学计量比，要么是通过燃烧碳分析。在本研究中，通过扫描电子显微镜（SEM）、X射线衍射（XRD）、拉曼光谱和静态碳核磁共振光谱（C NMR）对一系列热压ZrC的化学计量比进行了研究，并以此为基础校正C/Zr。在样品的C NMR光谱中观察到石墨、无定形和ZrC的碳特征信号，并且确定其强度会随烧结温度和化学计量比而变化。在本研究中，概述了一种量化ZrC和游离碳相化学计量比的方法，相对于仅使用广泛采用的整体碳燃烧分析并依赖该方法而言有了改进。我们报告称，与碳分析仪和名义方法相比，通过C NMR分析确定的C/Zr值要低得多。此外，还使用SEM和拉曼光谱分析了从ZrC结构中解离出来的碳的位置。
