title: Q(n) species distribution in K2O.2SiO2 glass by 29Si magic angle flipping NMR.
abstract: Two-dimensional magic angle flipping (MAF) was employed to measure the Q((n)) distribution in a (29)Si-enriched potassium disilicate glass (K(2)O.2SiO(2)). 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 k(3) = 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 zeta =-85.0 +/- 1.3 ppm, eta = 0.48 +/- 0.02 for Q((2)) and zeta = -74.9 +/- 0.2 ppm, eta = 0.03 +/- 0.01 for Q((3)) were observed in the potassium disilicate glass.
authors.affiliation: Department of Chemistry, The Ohio State University, 120 West 18th Avenue, Columbus, Ohio 43210-1173, USA.
authors.forename: Michael C
authors.initials: MC
authors.lastname: Davis
authors.forename: Derrick C
authors.initials: DC
authors.lastname: Kaseman
authors.forename: Sahar M
authors.initials: SM
authors.lastname: Parvani
authors.forename: Kevin J
authors.initials: KJ
authors.lastname: Sanders
authors.forename: Philip J
authors.initials: PJ
authors.lastname: Grandinetti
authors.forename: Dominique
authors.initials: D
authors.lastname: Massiot
authors.forename: Pierre
authors.initials: P
authors.lastname: Florian