Viscosity and Softening Behavior of Alkali Zinc Sulfophosphate Glasses

Abstract

We report on the softening properties and viscosity of glasses from the system ZnO–Na 2 O–SO 3 –P 2 O 5 for low‐temperature sealing applications. Up to a ratio of network‐forming ions PO 4 3− :SO 4 2− of about 2:1, a gradual substitution of P 2 O 5 by SO 3 results in decreasing glass transition and softening temperatures. At the same time, decreasing kinetic fragility is observed, noteworthy even for decreasing the total amount of network former from 44 at.% to 39 at.%. Thermomechanical and calorimetric analyses reveal a distinct SO 4 2− ‐promoted relaxation phenomenon at temperatures significantly below the macroscopic glass transition temperature, which is interpreted as a result of the formation of an increasingly interconnected assembly of SO 4 2− and PO 4 3− units with increasing SO 3 content.