Redox reactions during cooling of glass melts - A theoretical consideration

Abstract

Redox equilibria in glass melts and solid glasses, containing more than one polyvalent element are shifted during cooling if the enthalpy of the redox reaction is not zero. In the case of an iron-doped soda-lime-silica glass (Tg = 550 °C) the equilibrium cannot be frozen in above 600 °C even at a cooling rate of 10^3 Κ s^-1. At temperatures below 350 °C the equilibrium is completely frozen in even at cooling rates of 0.86 Κ d^-1. At the most suitable cooling rates (10^-3 to 1 Κ s^-1) the redox equilibrium is frozen in within the comparably small temperature range from 425 to 500 °C. These freezing-in temperatures depend on the type of polyvalent element but they can be calculated for all polyvalent ions, if the diffusion coefficients and their temperature dependences are known.