Abstract
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.
Highlights
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
nonbridging oxygen atoms (NBO) are preferentially associated with the higher field strength cation Ce2+. which results in reducing its content in the investigated glasses
Structural role of cerium is determined in borosilicate glasses by different modern techniques
Summary
Specific types of borosilicate glasses have long been the subject of structural studies [2] [5] [6] [7] This is because of their interest in both technical and academicals considerations. The structure of borosilicate glasses is based on the base former units which are the main constituents of the glass network These units are designed as, Qn in silicate [SiO4] and N4 or B4 in borate containing [BO3] and [BO4] structural species. The first region contains a limited concentration from CeO2 as a paramagnetic material In such a case, 29Si NMR study can be applied to obtain Qn values of different borosilicate glasses. 11B and FTIR spectroscopy are not affected by adding even more concentration from paramagnetic species from CeO2 These tools would be applied to obtain complementary data. 11B NMR & FTIR spectroscopy can be applied for all glass compositions while 29MAS NMR technique is limited to low CeO2 concentration (8 mol%)
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