Quantitative analysis of elastic moduli and structure of B2O3-SiO2 and Na2O-B2O3-SiO2 glasses

The average cross-link density (n) over bar (c), number of network bonds per unit volume n(b), average stretching force constant (F) over bar and atomic ring size have been calculated for the binary B2O3-SiO2 and ternary Na2O-B2O3-SiO2 glass systems. These data have been used to calculate the bond compression bulk modulus K-bc and Poisson's ratio sigma(cal) for each glass sample. The variation of these parameters and the ratio K-bc/K-c with composition were discussed quantitatively in terms of the change in structure of the glass network. The result showed that the connectivity and hence the rigidity of the B2O3-SiO2 glasses decreases with increasing B2O3 concentration. Whereas increasing of Na2O modifier in Na2O-B2O3-SiO2 glasses increase the cross-link density due to the transformation of three-fold-coordinated boron atoms into fourfold-coordinated ones. This in turn raises the resistance of the network to deformation and increases the observed density and elastic moduli of this glass system. Moreover, the theoretical elastic moduli have been obtained for each glass sample and compared with the corresponding experimental values. The results showed excellent agreement for the majority of the samples examined. (C) 2002 Elsevier Science B.V. All rights reserved.