Viscosity of Glass in the Transition Region in the Systems As-S, As-S-I and As-S-Tl

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The viscosity of glass in the systems As-S, As-S-I and As-S-Tl was measured by the beam-bending method at the temperature from the transition point to the deformation point. The plots of the logarithm of the viscosity versus the reciprocal of the absolute temperature are shown in Fig. 3, 4 and 5. From Fig. 3, it is clear that the slopes are more gentle with increase of S content above As2S3 in the system As-S. But in the systems As-S-I and As-S-Tl, on the other hand, they become, as shown in Fig. 4 and 5, more steep with increase of I and Tl contents, respectively.The isoviscosity temperature curves are shown in Fig. 6, 7 and 8. In the As-S glass the temperature required to make it isoviscous is lowered with increasing S content above As2S3 and also in the As-S-I glass it is rapidly lowered with I contents.Considering the linear relation in Fig. 3, 4 and 5, for the viscous flow of glass, the apparent activation energy can be calculated by the following equation; ΔE=Rd(logη)/d(1/T)1, where R is the gas constant. The results are shown in Fig. 9 and 10. In the As-S system, the activation energy has its peak at As2S3 and decreases rapidly around As2S8. In the As-S-I and As-S-Tl glass it increases with I and Tl contents respectively.The retarded elasticity appears remarkably in the transition region of the As-S glass and increases rapidly above As2S8. It has been recognized by Tsuchihashi et. al.6) that S8 rings begin to form in the glass when the S content is greater than that of As2S8-9.5. Therefore, from the above results we may suggest that the apparent activation energy for viscous flow decreases rapidly and the retarded elasticity increases with increase of S8 rings in the transition region.