Redox chemistry of iron-manganese and iron-chromium interactions in soda-lime-silica glass melts

Abstract

Glass melts are mostly not in a chemical equilibrium with a coexisting gas phase, it does not adjust before maintaining the melt at a constant temperature and a constant gas phase for hours. But the one-phase equilibrium between several polyvalent Clements in a melt above the glass transition temperature always exists, it adjusts spontaneously. Below the transition temperature the redox State is invariably frozen-in. The calculation of redox states must be based on the matter and Charge balance (stoichiometric equations) and equilibrium relations (mass-action law). Such a calculation of Schreiber's experimental results was consistently possible. Accordingly cooled glasses are free from Cr⁶⁺, if the glass contains Fe²⁺. To achieve this one has to melt oxidized chromium-containing glasses with sufficient iron content.