Ultrasonic and structural features of some borosilicate glasses modified with heavy metals

Abstract

A quaternary glass system Na 1.4 B 2.8 Si x Pb 0.3−x O 5.2+x , with 0 ≤ x ≤ 0.3, was prepared and studied by Fourier transform infrared spectroscopy, density and ultrasonic techniques to debate the issue of the role of SiO 2 in the structure of lead alkali borate glasses. The results indicate that SiO 2 generates an abundance of bridging oxygen atoms, [BO 4 ] and [SiO 4 ] structural units and changes the bonds B-O-B and Pb-O-B to Si-O-Si and B-O-Si. The latter bonds have higher bond strength and higher average force constant than the former bonds. Therefore, the glass structure becomes contracted and compacted, which decreases its molar volume and increases its rigidity. This concept was asserted from the increase in the ultrasonic velocity, Debye temperature and elastic moduli with the increase of SiO 2 content. The present compositional dependence of the elastic moduli was interpreted in terms of the electron-phonon anharmonic interactions and the polarization of Si 4+ cation. A good correlation was observed between the experimentally determined elastic moduli and those computed according to the Makishima-Mackenzie model.

Structural drivers controlling sulfur solubility in alkali aluminoborosilicate glasses

“…It is worth noting that as the network polymerization increases when Na 2 O is replaced by Al 2 O 3 , the molar volume also increases from 24.61 cm 3 /mole to 26.47 cm 3 /mole, whereas APF decreases from 0.33 to 0.31 (Figure A), indicating a more open structure having a higher free volume in the investigated glasses 38,81 . Though previous studies 10 have highlighted that the presence of available voids aids in sulfur incorporation, it did not ensure a positive trend in the present investigation.…”

“…10 It is worth noting that as the network polymerization increases when Na 2 O is replaced by Al 2 O 3 , the molar volume also increases from 24.61 cm 3 /mole to 26.47 cm 3 /mole, whereas APF decreases from 0.33 to 0.31 (Figure S5A), indicating a more open structure having a higher free volume in the investigated glasses. 38,81 Though previous studies 10 have highlighted that the presence of available voids aids in sulfur incorporation, it did not ensure a positive trend in the present investigation. This is interesting and its origins are likely attributed to the formation of 4-coordinated Al at the expense of non-framework Na + which imparts a higher rigidity to the glass structure as a result of the formation of Al−O−(Si, Al) directional bonds, 25,26 which then impedes the movement of sulfate units during its incorporation into borosilicate melts and thereby, suppressing sulfur loading in glassy matrix.…”

“…Given that there is no distinct difference in network polymerization and relative content of free oxygen with varying Li 2 O concentrations, the decrease in sulfur solubility with increasing Li 2 O/Na 2 O ratio can primarily be attributed to the increased compactness in the glass structure, as revealed by the increasing APF (Figure S5B), 81 which leads to smaller interstices in the glass network for sulfate units to be accommodated. The overall structural densification is also reflected by the decrease in average Na-O distance as revealed by the 23 Na NMR shift in Li-containing samples (30Na-5Li) in comparison to the Li-free (35Na-5Al) glass (Figure 5B).…”