29Si and 27Al MAS NMR study of the thermal transformations of kaolinite from North China
29Si and 27Al MAS NMR study of the thermal transformations of kaolinite from North China
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DOI：
10.1180/0009855033840114
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发表时间：
2003-12
期刊：
影响因子：
1.5
通讯作者：
H. He;J. G. Guo;J. Zhu;C. Hu
中科院分区：
文献类型：
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作者：
H. He;J. G. Guo;J. Zhu;C. Hu
摘要利用27 Al和29 Si魔角旋转核磁共振（MASNMR）、X射线衍射（XRD）、差热分析（DTA）和热重分析（TG）等方法研究了高岭石的热转变过程。实验结果表明，该样品是一种纯高岭石，其中含有约3%的碳质杂质。27 Al和29 Si MAS NMR谱表明，高岭石在450 - 1050°C热转变的显微结构演化与许多作者先前发表的高岭石-莫来石反应系列相似。莫来石在1190和1250°C下的29 Si MAS NMR光谱显示在~−87和−92 ppm处有两个共振，分别对应于Si周围的硅线石型几何结构和莫来石的典型Si环境。在1350°C时，莫来石的（hk 0）和（kh 0）发生劈裂，表明初生莫来石转变为正交莫来石。同时，~−92 ppm处的共振分裂为~ -90和−94 ppm处的两个信号。莫来石的27 Al MAS NMR谱由三个信号组成，分别集中在~ −4、45和60 ppm，分别对应于八面体、扭曲四面体和四面体Al位点。
Abstract The thermal transformations of kaolinite have been studied using 27Al and 29Si magic angle spinning nuclear magnetic resonance (MAS NMR), X-ray diffraction (XRD), differential thermal analysis (DTA) and thermogravimetric analysis (TG). The experimental results show that this sample is a pure kaolinite which contains ~3% carbonaceous material as impurity. 27Al and 29Si MAS NMR spectra show that the microstructural evolution of the thermal transformation of kaolinite at 450−1050°C is similar to that of the kaolinite- mullite reaction series previously published by many authors. 29Si MAS NMR spectra of mullite at 1190 and 1250°C display two resonances at ~−87 and−92 ppm, corresponding to sillimanite-type geometry around Si and the typical Si environment of mullite, respectively. At 1350°C, the splitting of (hk0) and (kh0) of mullite occurs, indicating that the primary mullite transforms into orthorhombic mullite. Simultaneously, the resonance at ~−92 ppm splits into two signals at ~ -90 and −94 ppm. 27Al MAS NMR spectra of the mullite consist of three signals centred at ~ −4, 45 and 60 ppm, corresponding to octahedral, distorted tetrahedral and tetrahedral Al sites, respectively.