| Two-dimensional magic angle flipping (MAF) was employed to measure the Q(n) distribution in a 29Si enriched potassium disilicate glass (K2O · 2 SiO2). Relative concentrations of [Q(4)] = 7.2% ± 0.3%, [Q(3)] = 82.9% ± 0.1%, [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 ppm, −91.32 ± 0.01 ppm, and −101.67±0.02, and standard deviations of 3.27±0.03 ppm, 4.19±0.01 ppm, and 5.09±0.03 for Q(2), Q(3), and Q(4), respectively. Additionally, nuclear shielding anisotropy values of z = −85.0 ± 1.3 ppm, h = 0.48 ± 0.02 for Q(2), and z = −74.9±0.2 ppm, h = 0.03±0.01 for Q(3) were observed in the potassium disilicate glass. |
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