Thomsen René M, Skibsted Jørgen, Yue Yuanzheng
Department of Chemistry and Bioscience , Aalborg University , 9220 Aalborg , Denmark.
Department of Chemistry and Interdisciplinary Nanoscience Center (iNANO) , Aarhus University , 8000 Aarhus C , Denmark.
J Phys Chem B. 2018 Mar 29;122(12):3184-3195. doi: 10.1021/acs.jpcb.7b12437. Epub 2018 Mar 20.
The structural arrangement of alkali-modified calcium aluminosilicate glasses has implications for important properties of these glasses in a wide range of industrial applications. The roles of sodium and potassium and their competition with calcium as network modifiers in peralkaline aluminosilicate glasses have been investigated by Al and Si MAS NMR spectroscopy. The Si MAS NMR spectra are simulated using two models for distributing Al in the silicate glass network. One model assumes a hierarchical, quasi-heterogeneous aluminosilicate network, whereas the other is based on differences in relative lattice energies between Si-O-Si, Al-O-Al, and Si-O-Al linkages. A systematic divergence between these simulations and the experimental Si NMR spectra is observed as a function of the sodium content exceeding that required for stoichiometric charge-balancing of the negatively charged AlO tetrahedra. Similar correlations between simulations and experimental Si NMR spectra cannot be made for the excess calcium content. Moreover, systematic variations in the Al isotropic chemical shifts and the second-order quadrupole effect parameters, derived from the Al MAS NMR spectra, are reported as a function of the SiO content. These observations strongly suggest that alkali ions preferentially charge-balance AlO as compared to alkaline earth (calcium) ions. In contrast, calcium dominates over the alkali ions in the formation of nonbridging oxygens associated with the SiO tetrahedra.
碱改性钙铝硅酸盐玻璃的结构排列对这些玻璃在广泛工业应用中的重要性能具有影响。通过铝和硅的魔角旋转核磁共振光谱研究了钠和钾在过碱性铝硅酸盐玻璃中作为网络改性剂的作用以及它们与钙的竞争关系。利用两种在硅酸盐玻璃网络中分布铝的模型对硅的魔角旋转核磁共振光谱进行了模拟。一种模型假定为分层的、准非均相的铝硅酸盐网络，而另一种模型则基于硅-氧-硅、铝-氧-铝和硅-氧-铝键之间相对晶格能的差异。随着钠含量超过使带负电荷的铝氧四面体达到化学计量电荷平衡所需的量，观察到这些模拟结果与实验硅核磁共振光谱之间存在系统性偏差。对于过量的钙含量，模拟结果与实验硅核磁共振光谱之间无法建立类似的相关性。此外，还报道了从铝的魔角旋转核磁共振光谱得出的铝各向同性化学位移和二阶四极效应参数随二氧化硅含量而变化的情况。这些观察结果有力地表明，与碱土（钙）离子相比，碱金属离子优先使铝氧电荷平衡。相反，在与硅氧四面体相关的非桥氧形成过程中，钙比碱金属离子占主导地位。
