Al coordination and speciation in calcium aluminosilicate glasses:: Effects of composition determined by 27Al MQ-MAS NMR and Raman spectroscopy

yThe structure and properties of glasses and melts in the CaO-Al2O3-SiO2 (CAS) system play an important role in earth and material sciences. Aluminum has a crucial role in this ternary system, and its environment is still questioned. In this paper, we present new results using Raman spectroscopy and Al-27 Nuclear Magnetic Resonance on CAS glasses obtained by classic and rapid quenching methods. We propose an Al/Si tetrahedral distribution in the glass network in different Q(n) species. In this system, we show that Al and Si are mainly in Q(4) species along the join R=CaO/Al2O3 = 1, and in depolymerized Q(2) and Q(3) units at high CaO content for other joins (R = 1.57 and 3). Five- (Al-[5]) and six-fold (Al-[6]) coordinated aluminum can be detected in the peraluminous glasses (R < 1) in agreement with the deficit of charge compensators, Ca2+ ions, near Al atoms. Unexpectedly, between 5% and 8% of Al-[5] is also observed for percalcic glasses (R > 1), except for glasses with low silica and high CaO content. The presence of Al-[5] is related to viscous flow mechanisms while, in highly depolymerized glasses, the absence of Al-[5] may indicate different mechanisms for melts to flow. This systematic study on the CAS system modifies the simple picture of aluminosilicate glasses, and the existence of Al-[5] should be included by geochemists, geophysicists and glass scientists to model appropriately the physical properties of aluminosilicate glasses and melts. (c) 2006 Elsevier B.V. All tights reserved.

CaO - Al₂O₃ - SiO₂（CAS）体系中玻璃和熔体的结构与性质在地球科学和材料科学中起着重要作用。铝在这个三元体系中具有关键作用，其环境仍存在争议。在本文中，我们利用拉曼光谱和²⁷Al核磁共振技术，对通过常规和快速淬火方法获得的CAS玻璃给出了新的研究结果。我们提出了玻璃网络中不同Q(n)物种的Al/Si四面体分布。在该体系中，我们表明沿着R = CaO/Al₂O₃ = 1的连接线，Al和Si主要以Q(4)物种存在，而对于其他连接线（R = 1.57和3），在高CaO含量时则以解聚的Q(2)和Q(3)单元存在。在过铝质玻璃（R < 1）中可以检测到五配位（Al - [5]）和六配位（Al - [6]）的铝，这与Al原子附近电荷补偿剂Ca²⁺离子的缺失相符。出乎意料的是，在过钙玻璃（R > 1）中，除了低硅和高CaO含量的玻璃外，也观察到5% - 8%的Al - [5]。Al - [5]的存在与粘性流动机制有关，而在高度解聚的玻璃中，Al - [5]的缺失可能表明熔体流动的机制不同。对CAS体系的这项系统研究改变了铝硅酸盐玻璃的简单图景，地球化学家、地球物理学家和玻璃科学家在对铝硅酸盐玻璃和熔体的物理性质进行适当建模时应考虑Al - [5]的存在。（c）2006 Elsevier B.V. 保留所有权利。