CaF2-Al2O3-MgO电渣微结构的原位拉曼光谱及27Al魔角旋转核磁共振研究

运用原位拉曼光谱和 ²⁷Al魔角旋转核磁共振研究了CaF₂-Al₂O₃-MgO电渣重熔渣晶体、 玻璃和熔体的微结构及铝配位数的变化. 利用X射线粉末衍射分析获得该晶体样品中存在的物相, 分别基于密度泛函理论及量子化学从头算分析了S-6530晶体和熔体中相关物相的拉曼振动波数及散射活性, 并对其主要振动模式进行了归属. 结果表明, S-6530晶体中铝主要以六配位形式存在, 并有少量的四、 五配位. 在升温过程中, 其中MgAl₂O₄物相的Al-O多面体由AlO₆]转变成AlO₄]与AlO₅]共存. Al在熔体和玻璃结构中主要以AlO₄]四面体的形式存在, 其占比高达71.1%, 相较于其晶态, AlO₅]的占比也增加至28.6%. 基于构建的熔体团簇模型的量子化学从头算表明, AlO₄]构型倾向于以Q₃, Q₄连接方式为主的层状和架状结构, 而AlO₅]构型则倾向于单体形式.

In-situ Studies of Microstructure of CaF2-Al2O3-MgO Electroslag by Raman Spectroscopy and 27Al MAS NMR†

The microstructure and Al coordination of crystalline, glassy and molten states of CaF₂-Al₂O₃-MgO electroslag remelting slag were investigated by in-situ Raman spectroscopy and ²⁷Al magic angle spinning nuclear magnetic resonance(MAS NMR). X-Ray diffraction was used to analyze phase of the crystal sample. Raman vibrational wavenumber and scattering activity of S-6530 crystal and melt were calculated based on density functional theory(DFT) and ab initio quantum chemical studies, respectively, and the major vibrational modes were assigned. The results showed that six-fold coordinated aluminum mainly exists in the S-6530 crystal, supplemented by a small amount of four or five-fold coordinated aluminum. During the heating process, the Al—O polyhedron of MgAl₂O₄ phase is transformed from AlO₆] to AlO₄] or AlO₅]. Al is present predominantly in AlO₄] tetrahedron in both S-6530 glass and melt, the proportion of AlO₄] is as high as 71.1%, compared with its crystalline state, the proportion of AlO₅] also increases to 28.6%. Based on quantum chemistry ab-initio calculation of the constructed molten cluster models, the AlO₄] configuration tends to be layered and frame structure dominated by Q₃ and Q₄ connections, and AlO₅] configuration remains isolated.