Method for Measuring Viscosity of Glass in Relation to Contraction by Compressive Stress

Abstract

The fiber elongation method is possible to measure the viscosity of glass over a range from 108 to 1015 poises. But it is not easy to measure the viscosity of non-oxide glasses such as chalcogenide glasses, since the preparation of samples needs the forming by heating.The viscosity of non-oxide glass as well as oxide glass are measured over a range from 1010 to 1013 poises, using a thermodilatometer shown in Fig. 1. In a practical experiment soda-lime-silica glass, NBS 710, of which temperature-viscosity characteristic is known, has been used as oxide glass, and chalcogenide glass, arsenic triselenide synthesized by authors has been done as non-oxide glass. These samples are of pillar shape (3×3×20mm). Instantaneously exerting compressive stress caused by applied load (20 or 50g) on the sample, strain-time curves shown in Fig. 2 or 3 are obtained. These experimental results can be explained well by rheological 4-elements model shown in Fig. 4 in the same manner as the fiber elongation. Therefor the viscosity of glass at constant temperature is obtained by following equation, η=mg/S(-Δl/l0)/Δt, where η is the viscosity of glass (poise); mg, the applied load (dyne); S, the sectional area of sample; and (-Δl/l0)/Δt, a tangent of the linear part of curves in Fig. 2 or 3. Measured viscosity values of NBS 710 are given in Table 1. These results show that the viscosity obtained by the fiber elongation method is normal viscosity, while the viscosity by this compressive method is shear viscosity.