| Autor: |
Logrado, Millena, Youngman, Randall E., Aitken, Bruce G., Eckert, Hellmut |
| Zdroj: |
The Journal of Physical Chemistry - Part C; August 2023, Vol. 127 Issue: 34 p17269-17284, 16p |
| Abstrakt: |
The modification of the glass structure in the system SiO2–P2O5–Al2O3by Na2O has been studied along the composition line 70SiO2–7.5P2O5–(22.5 – x)Al2O3–xNa2O (0 ≤ x≤ 17.5) using Raman spectroscopy and multinuclear solid state NMR of 29Si, 31P, 23Na, and 27Al nuclei. Spectral deconvolutions have been proposed based on 31P/23Na and 31P/27Al double resonance and 31P double-quantum filtering experiments, leading to a detailed picture of the short- and medium-range order in this glass system. The structure of these glasses is dominated by a significant bonding preference between formally anionic four-coordinate aluminum Al4species and formally cationic phosphate P4units (Al–O–P linkages). In the notation used here, the superscript denotes the number of bridging oxygen atoms bound to the network forming unit. The gradual replacement of alumina by sodium oxide initially (I) decreases the amount of higher coordinate aluminum and increases the number of Si–O–Al linkages, which are charge balanced by the sodium ions introduced by Na2O. Higher levels of x(II) lead to a partial depolymerization of Al–O–P linkages and the formation of anionic phosphate species (P2and P1) strongly interacting with the sodium ions. While Al–O–P linkages continue to be present for these anionic units, (III) some P–O–P linkages are also formed around x= 15.0, leading to the partial crystallization of sodium pyrophosphate at x= 17.5. There is no evidence for any modification of the silica component, which remains of the Si4type throughout the glass composition range. The results of the present study highlight the dual role of the sodium ions in the modification of the network structure of this three-component network former system in a quantifiable manner. |
| Databáze: |
Supplemental Index |
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