Influence of redox conditions on the isothermal workability of glass melts

Abstract

The influence of various redox ratios on the isothermal workability of glass melts is investigated by means of ultrasonic waves and mainly by the cylinder-compression method. The experiments were made with laboratory glass melts of float glass composition containing 0.22 wt% iron oxide for which the redox ratio Fe2+/Fetotal was varied between 14 and 84 % (melting history or redox prehistory). Properties are measured being responsible for the brittleness or stiffness and for the isothermal workability of a glass melt (non-Newtonian flow behaviour, relaxation modulus and high-temperature tensile strength). The main results are that a reduced glass melt shows a better isothermal (and isochomal) workability than an oxidised one. This means a better high-temperature tensile strength and a lower relaxation modulus and therefore a lower brittleness and rigidity of the reduced melt as well as lower compression and elastic moduli. Besides that, interesting alterations within the melts could be detected by means of spectroscopic investigations such as a shift of the iron absorption bands depending on the thermal, pressure and redox prehistory. The influence of different OH- contents and the problem of the origin of the amber colour were considered intensively.