Microstructure of complicated glasses in the system 30Na2O-2Al2O3-25 SiO2-xCeO2 (43-x) B2O3, x changes from 0.5 to 20 mol% have been extensively studied. Structural determination of glasses containing high cerium oxid...Microstructure of complicated glasses in the system 30Na2O-2Al2O3-25 SiO2-xCeO2 (43-x) B2O3, x changes from 0.5 to 20 mol% have been extensively studied. Structural determination of glasses containing high cerium oxide content (≥8 mol% CeO2) was carried out by 11B NMR and FTIR spectroscopy. On the other hand, 29Si MAS NMR experiment is hardly to be applied to glasses of CeO2 > 8 mol%. This is due to the paramagnetic action which is raised by cerium cations causing dilution or delaying in the resonance phenomenon. It is evidenced from NMR data that sodium oxide is high enough to modify the glass forming units which constitute the skeleton of the glass. Ceria is as well as silica and B2O3 all are acting as glass forming species. Decreasing of both fraction of boron tetrahedral units (N4) and chemical shift of silicon nuclei (δ) confirm the role of CeO2 as a glass former. On the other hand, fast decrease in N4 and chemical shift of Si nuclei with further increasing CeO2 contents (≥8 mol%) gives a clear evidence that the ability of cerium oxide to participate as a network former increases with increasing its content. New approach is applied to determine the fraction of CeO4 as a glass forming units. In this approach, we use the common advantage of 11B NMR and FTIR spectroscopy to obtain Ce4 fraction. The latter species cannot be determined from NMR spectroscopy, since very high relaxation time and magnetization of ceria cause intensive spectral broadening which prevent resonance spectra to be appeared.展开更多
文摘Microstructure of complicated glasses in the system 30Na2O-2Al2O3-25 SiO2-xCeO2 (43-x) B2O3, x changes from 0.5 to 20 mol% have been extensively studied. Structural determination of glasses containing high cerium oxide content (≥8 mol% CeO2) was carried out by 11B NMR and FTIR spectroscopy. On the other hand, 29Si MAS NMR experiment is hardly to be applied to glasses of CeO2 > 8 mol%. This is due to the paramagnetic action which is raised by cerium cations causing dilution or delaying in the resonance phenomenon. It is evidenced from NMR data that sodium oxide is high enough to modify the glass forming units which constitute the skeleton of the glass. Ceria is as well as silica and B2O3 all are acting as glass forming species. Decreasing of both fraction of boron tetrahedral units (N4) and chemical shift of silicon nuclei (δ) confirm the role of CeO2 as a glass former. On the other hand, fast decrease in N4 and chemical shift of Si nuclei with further increasing CeO2 contents (≥8 mol%) gives a clear evidence that the ability of cerium oxide to participate as a network former increases with increasing its content. New approach is applied to determine the fraction of CeO4 as a glass forming units. In this approach, we use the common advantage of 11B NMR and FTIR spectroscopy to obtain Ce4 fraction. The latter species cannot be determined from NMR spectroscopy, since very high relaxation time and magnetization of ceria cause intensive spectral broadening which prevent resonance spectra to be appeared.
