Effect of Network Polymerization on the Pressure-Induced Structural Changes in Sodium Aluminosilicate Glasses and Melts: 27Al and 17O Solid-State NMR Study

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• 作者：Sung Keun Lee ; Yoo Soo Yi ; George D. Cody ; Kenji Mibe ; Yingwei Fei ; Bjorn O. Mysen
• 刊名：The Journal of Physical Chemistry C
• 出版年：2012
• 出版时间：January 26, 2012
• 年：2012
• 卷：116
• 期：3
• 页码：2183-2191
• 全文大小：1113K
• 年卷期：v.116,no.3(January 26, 2012)
• ISSN：1932-7455

文摘

Probing the pressure-induced structural changes and the extent of disorder in aluminosilicate glasses and melts at high pressure remains a challenge in modern physical and chemical sciences. With an aim of establishing a systematic relationship between pressure, composition, and glass structures, we report ²⁷Al and ¹⁷O 3QMAS NMR spectra for sodium aluminosilicate glasses [Na₂O:Al₂O₃:SiO₂ = 1.5:0.5:2n with n = 1 (NAS150520, X_SiO2 = 0.5), 2 (NAS150540, X_SiO2 = 0.67), and 3 (NAS150560, X_SiO2 = 0.75)], quenched from melts at pressures up to 8 GPa. We also explore the stability of the ^[4]Al鈥揙鈥?sup>[4]Al cluster in the highly depolymerized, NAS150520, glass at high pressure. For given glass composition, the ^[5,6]Al peak intensity increases with increasing pressure. The population of ^[5,6]Al increases linearly with X_SiO2 from NAS150520 (X_SiO2 = 0.5) to NAS150560 glass (X_SiO2 = 0.75) at both 6 and 8 GPa. The ^[5,6]Al/X_SiO2 ratio also tends to increase with pressure, indicating a possible relationship between ^[5,6]Al fraction and X_SiO2 that depends on pressure. The effect of pressure on the network connectivity in the sodium aluminosilicate glasses is manifested in the increase in ^[4]Si鈥揙鈥?sup>[5,6]Al peak intensity and the decrease in the nonbridging oxygen (NBO) fraction with increasing pressure. The fraction of ^[4]Si鈥揙鈥?sup>[5,6]Al in NAS150520 is smaller than in NAS150560. Taking into consideration the pressure-induced Al coordination transformation in the fully polymerized glass (albite, Na₂O:Al₂O₃:SiO₂= 1:1:6, NBO/T = 0), the fraction of ^[5,6]Al at a given pressure varies nonlinearly with variations of NBO/T. ^[5,6]Al fraction at 8 GPa increases with decreasing degree of melt polymerization from 8% for fully polymerized albite melt (NBO/T = 0) to 37% for partially depolymerized melt (NAS150560, at NBO/T = 0.29). Then it gradually decreases to 15% for NAS150520 with further increase in NBO/T of 0.67. This observed trend in the densification behavior at a given pressure indicates competing densification mechanisms involving steric hindrance vs changes of NBO fraction in the silicate melts. The NMR results also suggest that both NBO and BO, particularly ^[4]Si鈥揙鈥?sup>[4]Si, interact with Na⁺, and thus the Na⁺ distribution is likely to be homogeneous around both NBO and BO at high pressure without spatial segregation of silica-rich and alkali-rich domains for the glass compositions studied here. The presence of the ^[4]Al鈥揙鈥?sup>[4]Al cluster is distinct in the NMR spectrum for NAS150520 glass at both 6 and 8 GPa. A new scheme of pressure-induced structural transitions in silicate melts involving ^[4]Al鈥揙鈥?sup>[4]Al includes the formation of ^[4]Al鈥揙鈥?sup>[5]Al.