NMR evidence for excess non-bridging oxygen in an aluminosilicate glass
NMR evidence for excess non-bridging oxygen in an aluminosilicate glass
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DOI：
10.1038/36312
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发表时间：
1997-11
期刊：
影响因子：
64.8
通讯作者：
J. Stebbins;Zhi Xu
中科院分区：
文献类型：
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作者：
J. Stebbins;Zhi Xu
最常见的人造玻璃含有铝硅酸盐成分，这种玻璃也是由快速冷却的岩浆形成的。氧是这些材料中最丰富的元素，它占据“桥接”（BO）或“非桥接”（NBO）位点。BOs连接了两个alo4或sio4四面体，从而在铝硅酸盐网络的最小结构单元之间提供了强而持久的键。nbo在一个四面体阳离子（Al或Si）和一个或多个网络修饰剂阳离子（如Ca2+或Na+）之间提供了相对较弱的连接，这些阳离子不是四面体网络的组成部分。这些弱键NBOs的相对丰度对于决定铝硅酸盐玻璃和熔体的热力学和动力学性质至关重要。对于“构造硅酸盐”组成的玻璃，其中改性剂阳离子的电荷等于铝原子的数量（如naalsi3o8或CaAl2Si2O8），玻璃结构的传统观点是只有BOs存在。在这里，我们提出了与这一观点相矛盾的实验观察。我们对CaAl2Si2O8的核磁共振测量，直接确定了BO和NBO的相对丰度，表明相当数量的NBO可以存在于构造硅酸盐玻璃中。这些多余的nbo会增加相应液体的熵和热容，降低其粘度，并改变流动和扩散机制。由于最常见的流纹岩岩浆和玻璃陶瓷的熔融前体具有近构造硅酸盐成分，我们的结果需要重新评估控制地球和工业中许多过程的高温液体性质。
The most common of man-made glasses have aluminosilicate compositions, and such glasses also form from rapidly cooling magmas. Oxygen is the most abundant element in these materials, where it occupies either ‘bridging’ (BO) or ‘non-bridging’ (NBO) sites. BOs link two AlO4or SiO4tetrahedra, thereby providing strong, long-lived bonds between the smallest structural units of the aluminosilicate network. NBOs provide a relatively weak connection between one tetrahedral cation (Al or Si) and one or more network modifier cations — such as Ca2+or Na+— that are not an integral part of the tetrahedral network. The relative abundance of these weakly bonded NBOs is critical in determining the thermodynamic and dynamical properties of aluminosilicate glasses and melts,,. For glasses of ‘tectosilicate’ composition, where the charge of the modifier cation equals the number of aluminium atoms (as in NaAlSi3O8or CaAl2Si2O8), the conventional view of glass structure is that only BOs are present,. Here we present experimental observations that contradict this view. Our NMR measurements of CaAl2Si2O8, which determine directly the relative abundances of BO and NBO, indicate that a considerable amount of NBO can be present in a tectosilicate glass. These excess NBOs will increase the entropy and heat capacity of the corresponding liquid and decrease its viscosity, as well as modifying flow and diffusion mechanisms,. As the most common rhyolitic magmas and the molten precursors of glass ceramics have near-tectosilicate compositions,, our results require a reassessment of the high-temperature liquid properties that control many processes in the Earth and in industry.