Q(n) Species Distribution in K2O·2SiO2 Glass by 29Si Magic Angle Flipping NMR

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• 作者：Michael C. Davis ; Derrick C. Kaseman ; Sahar M. Parvani ; Kevin J. Sanders ; Philip J. Grandinetti ; Dominique Massiot ; Pierre Florian
• 刊名：Journal of Physical Chemistry A
• 出版年：2010
• 出版时间：May 6, 2010
• 年：2010
• 卷：114
• 期：17
• 页码：5503-5508
• 全文大小：209K
• 年卷期：v.114,no.17(May 6, 2010)
• ISSN：1520-5215

文摘

Two-dimensional magic angle flipping (MAF) was employed to measure the Q⁽ⁿ⁾ distribution in a ²⁹Si-enriched potassium disilicate glass (K₂O·2SiO₂). Relative concentrations of [Q⁽⁴⁾] = 7.2 ± 0.3%, [Q⁽³⁾] = 82.9 ± 0.1%, and [Q⁽²⁾] = 9.8 ± 0.6% were obtained. Using the thermodynamic model for Q⁽ⁿ⁾ species disproportionation, these relative concentrations yield an equilibrium constant k₃ = 0.0103 ± 0.0008, indicating, as expected, that the Q⁽ⁿ⁾ species distribution is close to binary in the potassium disilicate glass. A Gaussian distribution of isotropic chemical shifts was observed for each Q⁽ⁿ⁾ species with mean values of −82.74 ± 0.03, −91.32 ± 0.01, and −101.67 ± 0.02 ppm and standard deviations of 3.27 ± 0.03, 4.19 ± 0.01, and 5.09 ± 0.03 ppm for Q⁽²⁾, Q⁽³⁾, and Q⁽⁴⁾, respectively. Additionally, nuclear shielding anisotropy values of ζ =−85.0 ± 1.3 ppm, η = 0.48 ± 0.02 for Q⁽²⁾ and ζ = −74.9 ± 0.2 ppm, η = 0.03 ± 0.01 for Q⁽³⁾ were observed in the potassium disilicate glass.