Electric field-induced softening of alkali silicate glasses

Motivated by the advantages of two-electrode flash sintering over normal sintering, we have investigated the effect of an external electric field on the viscosity of glass. The results show remarkable electric field-induced softening (EFIS) as application of DC field significantly lowers the softening temperature of glass. To establish the origin of EFIS, the effect is compared for single vs. mixed-alkali silicate glasses with fixed mole% of the alkali ions such that the mobility of alkali ions is greatly reduced while the basic network structure does not change much. Sodium silicate and lithium-sodium mixed alkali silicate glasses were prepared by standard melt-quench method. The samples were tested mechanically in situ under compression in external electric field ranging from 0 to 250 V/cm in specially designed equipment. A creep tester was modified to track viscous displacement of glass while a measurement circuit was built to record voltage across and current though the sample. The circuit was designed to carefully measure current within six orders of magnitude. A comparison of data for different compositions indicates a complex mechanical response due to Joule heating, electrolysis, dielectric breakdown and field-assisted viscous flow.