Lead borosilicate glasses having general formulae (PbO)0.5 −x(SiO2)0.5(B2O3)x with 0.0 ≤ x ≤ 0.4 and (PbO)0.5(SiO2)0.5 −y(B2O3)y with 0.0 ≤ y ≤ 0.5 have been prepared by a conventional melt–quench method and characterized by 29 Si, 11 B magic angle spinning (MAS) NMR techniques and infrared spectroscopy, as regards their structural features. From 29 Si NMR results, it has been inferred that with increasing concentration of boron oxide, (PbO)0.5 −x(SiO2)0.5(B2O3)x glasses exhibit a systematic increase in the number of Q4 structural units of Si at the expense of Q2 structural units, along with the formation of Si–O–B linkages. On the other hand, for (PbO)0.5(SiO2)0.5−y(B2O3)y glasses, there is no direct interaction between SiO2and B2O3 in the glass network, as revealed by the 29 Si MAS NMR studies. Boron exists in both trigonal and tetrahedral configurations for these two series of glasses and for the (PbO)0.5(SiO2)0.5−y(B2O3)y series of glasses; the relative concentration of these two structural units remains almost constant with increasing B2O3 concentration. In contrast, for (PbO)0.5−x(SiO2)0.5(B2O3)x glasses, there is a slight increase in the number of BO3 structural units above x = 0.2, as there is a competition between SiO2 and B2O3 for interaction with Pb2+, thereby leading to the formation of BO3 structural units. For both series of glasses, the thermal expansion coefficient is found to decrease with increasing B2O3 concentration, the effect being more pronounced for the (PbO)0.5 −x(SiO2)0.5(B2O3)x series of glasses due to the increased concentration of Q4structural units of silicon and better cross-linking as a result of the formation of Si–O–B-type linkages.

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Phosphate glasses having composition, 40Na 2 O-10BaO-xB 2 O 3-(50-x)P 2 O 5 , where x = 0-20 mol% were prepared using conventional melt quench technique. Density of these glasses was measured using Archimedes principle. Microhardness (MH) was measured by Vicker's indentation technique. Structural studies were carried out using IR spectroscopy and 31 P and 11 B MAS NMR. Density was found to vary between 2⋅ ⋅62 and 2⋅ ⋅77 g/cc. MH was found to increase with the increase in boron content. 31 P MAS NMR spectra showed the presence of middle Q 2 groups and end Q 1 and Q 0 groups with P-O-B linkages. FTIR studies showed the presence of BO 3 and BO 4 structural units along with the depolymerization of phosphate chains in conformity with 31 P MAS NMR. 11 B NMR spectra showed increase in BO 4 structural units with increasing boron content. The increase in MH with B 2 O 3 content is due to the increase of P-O-B linkages and BO 4 structural units as observed from MAS NMR studies resulting in a more rigid borophosphate glass networks.

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