Abstract
The elastic properties of the glasses in the systems xR2O⋅B2O3⋅rSiO2 (0<x<1.3; r=1 and 2; R=Na and K) and yNa2O⋅(1-y)B2O3 have been measured by the pulse transmission method. The elastic constants of the glasses in the sodium borate systems with and without 5mol% MgO exhibited a maximum at the molar ratio (MgO+Na2O)/B2O3=0.5. This composition is equivalent to that at which the fraction N4 of the four-coordinated boron atoms in those glasses deviates from the relation N4=(MgO+Na2O)/B2O3. Therefore the elastic constant is expected to play a role indicating the composition with the maximum value of N4 and the formation of non-bridging oxygens. The results in the alkali borate glasses have been applied to the borosilicate glasses in order to estimate the composition at which the N4 becomes maximum and also to assure if the potassium oxide plays the same role as the sodium oxide. The log-log plot of the bulk modulus vs, the mean atom-pair volume verifies the previous model of the borosilicate glasses (Takahashi et al., J. Non-Cryst. Solids, in print). The effect of SiO2 content on the elastic properties of the borosilicate glasses has been discussed also.
