Stress Relaxation of Glass in the Systems As-S and As-Se

Abstract

Stress relaxation of glasses in the systems As-S and As-Se was measured by the torsional method near the transition temperature (relaxation modulus of 1010-108dyne/cm2). Time-temperature superpositions of each run for all samples were successful in this range. And so, at the fixed temperature (the temperature of isoviscosity, η=2×1013poise) we could draw master curves for all samples as shown in Fig. 5, 6 and 7. As to the shift factor, aT, the plots of logaT vs. 1/T give essentially a straight line for each sample as shown in Fig. 9 and 10. Therefore, for the stress relaxation of glass, the apparent activation energy can be calculated by the following equation, ΔE=Rd(logaT)/d(1/T), where R is the gas constant. The results are shown in Fig. 11. In the As-S system, the activation energy is high at As2S3 and goes through an unusual maximum around As2S8. In the As-Se system, the activation energy is high at As2Se3 and decreases with increasing Se content. But it increases again with Se contents above 80 atomic per cent.The distribution of relaxation time can be expressed approximately as follows, H(τ)=-{Gr(t)⋅dlogGr(t)/dlogt}t=τ. The results are shown in Fig. 12, 13 and 14. The distribution curves for all the samples go through the maximum. The peak appears at the longest period for As2S3 and As2Se3 glasses in As-S and As-Se systems, respectively, and shifts from long time to short time with increasing S and Se contents. The relaxation moduli at t=0 are shown in Fig. 15 and are the largest for As2S3 and As2Se3 glasses in the systems As-S and As-Se, respectively.