Density of Borate Glass Melts

Abstract

In the present experiment the densities of melts in the system Li₂O-B₂O₃, Na₂O-B₂O₃, K₂O-B₂O₃, BaO-B₂O₃, SrO-B₂O₃, Li₂O-K₂O-B₂O₃, Li₂O-Na₂O-B₂O₃, and K₂O-BaO-B₂O₃ were measured by a counterbalanced-sphere method at temperatures ranging approximately from 800° to 1250°C. The results of the measurement are shown in Table 1, Fig. 1, Fig. 2 and Fig. 3. The more direct way of showing the effect of addition of alkali oxide upon B-O network in alkali borate glass is to study the apparent molar volume (V) calculated from the density data as a function of composition. Fig. 4 illustrates the effect of alkali oxide addition upon the molar volume of the melts. The comparison of the data of the three systems shows that the apparent molar volume of the lithiumborates is definitely lower than that of the two other alkali borates. On a mole basis the order of the contracting effect of the B-O network is Li>Na<K. A similar observation can be made for the data of BaO-B₂O₃ and SrO-B₂O₃ glass melts as shown in Fig. 5.
The relationships between the apparent molar volume of binary alkali-borate glasses and alkali oxide content are shown in Fig. 7 and Fig. 9. If one alkali oxide is progressively substituted for another it is found that the molar volume varies linearly with the molar fraction of alkali oxide substituted when the molar fraction of B₂O₃ is constant.