Multinuclear solid-state NMR investigation of local structure in aluminosilicate cementitious materials

硅铝酸盐胶凝材料局部结构的多核固态核磁共振研究

• 批准号: 1801874
• 金额: --
• 依托单位: University of St Andrews
• 依托单位国家: 英国
• 项目类别: Studentship
• 财政年份: 2016
• 资助国家: 英国
• 起止时间: 2016 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=studentship-1801874
• 关键词: Multinuclear; solid; state; NMR; investigation

Secondary cementitious materials are materials added to cements in order to produce desirable properties (such as high compressive strength). It has been found that amongst the wide variety of materials trialled, slags produce the best properties. Cementitious materials are known to contain structural disorder, and as a result diffraction-based techniques, where the time and space averaged structure of a material is studied, are of limited utility for their characterisation. By contrast, solid-state MAS NMR provides a powerful probe of the local structure of materials, through the interactions that affect the NMR parameters, making it ideally placed for characterisation of disordered materials.Previous low-field MAS NMR studies of the cementitious materials under study in this project have found a correlation between desirable properties (high compressive strength) and the presence of low-coordinate Si and Al. Neither the mechanism of formation or the structure-property relationship whereby low coordination species provide high compressive strength is fully understood. Therefore, throughout the course of this PhD structural characterisation of a range of materials and an investigation the local geometry of Al, Si and other cationic species will be carried out using multinuclear solid-state NMR spectroscopy.A series of samples have been previously prepared and have been initially investigated using X-ray diffraction, X-ray fluorescence and low field 29Si and 27Al MAS NMR spectroscopy. Initially, further investigation of these samples will be carried out by performing higher field conventional 27Al and 29Si (and possibly 25Mg and 43Ca) MAS NMR experiments, and two-dimensional 27Al MQMAS and 27Al-29Si heteronuclear correlation experiments. The structural disorder in these materials causes the broadening and overlapping of peaks in the NMR spectra, and so spectra will require analytical fitting in order to identify individual peaks and, for quadrupolar nuclei, fitting using a Czjzek distribution of quadrupolar parameters will be needed in order to extract information on the distribution of NMR parameters present. The higher resolution offered by MQMAS spectra will enable the number and type of low coordinate Al species present be determined. An analysis of aluminosilicate materials with different chemical composition, structure, origin etc. will be performed, investigating, in particular, the number and type of Si and Al species and their coordination number in order to try and understand how these are related. The effect of high temperature heating on the formation of low coordinated Al and Si will also be investigated by varying the temperature, the time spent heating and other possible parameters. NMR will be used to investigate the local structure in these materials and it is anticipated that this will provide valuable information on both the mechanism the formation of low coordinate species and on how to design and synthesise materials with optimal chemical composition and structure.Interpretation of experimental NMR data will be aided by using DFT calculations, where possible, typically on model systems, using planewave basis sets and the GIPAW approach for calculating NMR parameters.

次要胶凝材料是添加到水泥中以产生所需性质（例如高抗压强度）的材料。已经发现，在所试验的各种材料中，炉渣产生最好的性能。已知水泥基材料包含结构无序，并且因此基于衍射的技术（其中研究材料的时间和空间平均结构）对于它们的表征具有有限的实用性。相比之下，固态MAS NMR通过影响NMR参数的相互作用，使其成为表征无序材料的理想场所。本项目中所研究的胶凝材料的先前低场MAS NMR研究发现了理想性能之间的相关性（高压缩强度）和低配位Si和Al的存在。低配位物质提供高压缩强度的形成机制或结构-性能关系都没有完全理解。因此，在本博士学位的整个过程中，将使用多核固态NMR光谱对一系列材料的结构表征和Al，Si和其他阳离子物种的局部几何结构进行研究。之前已经制备了一系列样品，并使用X射线衍射，X射线荧光和低场29 Si和27 Al MAS NMR光谱进行了初步研究。最初，这些样品的进一步调查将进行高场常规27铝和29硅（可能25镁和43钙）MAS NMR实验，和二维27铝MQMAS和27铝-29硅异质结相关实验。这些材料中的结构无序导致NMR光谱中峰的加宽和重叠，因此光谱将需要分析拟合以识别各个峰，并且对于四极核，将需要使用四极参数的Czjzek分布进行拟合以提取关于存在的NMR参数的分布的信息。MQMAS光谱提供的更高分辨率将使低配位Al物种的数量和类型得以确定。将对具有不同化学组成、结构、来源等的铝硅酸盐材料进行分析，特别是研究Si和Al物种的数量和类型及其配位数，以尝试了解这些之间的关系。还将通过改变温度、加热时间和其他可能的参数来研究高温加热对形成低配位Al和Si的影响。NMR将用于研究这些材料的局部结构，预计这将为低配位物种的形成机制以及如何设计和合成具有最佳化学组成和结构的材料提供有价值的信息。实验NMR数据的解释将通过使用DFT计算来帮助，在可能的情况下，通常在模型系统上，使用平面波基组和GIPAW方法计算NMR参数。