Editorial |
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Authors: | WJ Dell PJ Bray SZ Xiao |
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Institution: | Department of Physics, Brown University, Providence, RI 02912, USA;Glass Laboratory, Beijing Glass Research Institute, Hong-Qiao, Beijing 100062, Peoples Republic of China |
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Abstract: | NMR techniques are employed to determine the relative fractions of boron atoms in Na2OB2O3SiO2 glasses of high soda content. The data show that if enough Na2O is added, four-coordinated borons are destroyed and borons with one or two non-bridging oxygens are created, but that both the beginning point and the rate of these processes depend strongly on the amount of silica present. These findings are shown to be quantitatively inconsistent with structural models previously suggested in the literature. Utilizing the concept of proportionate atomic sharing of the additional Na2O, a new structural model is proposed for K 8 (K = mol% SiO2/mol% B2O3) which is consistent with all the data including previously reported data for glasses in the region of relatively low soda content. Using R = mol% Na2O/mol% B2O3, the new model states that for , all the additional Na2O is employed in forming non-bridging oxygens on the silica tetrahedra; then for RD1 R RD3 = 2 + K, the fraction of the additional Na2O destroys reedmernerite groups and forms pyroborate units plus silica tetrahedra with two non-bridging oxygens per Si atom, while the fraction of the additional Na2O destroys diborate groups and forms additional pyroborate units. |
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