Electron exchange reactions between polyvalent elements in soda-lime-silica and sodium borate glasses

Abstract

In oxidic glasses the redox State of polyvalent elements is determined by the oxygen partial pressure with which the melt is in equilibrium. However, if a second polyvalent element is introduced the redox ratios at a given oxygen pardal pressure change for both elements. This interaction is interpreted in terms of electron exchange reactions during cooling. The direcdon of the electron exchange and the amount of exchanged electrons are calculated from the Standard reaction enthalpy and Standard reaction entropy of the involved polyvalent elements. Oxygen balance calculations are carried out based on literature data available for iron/chromium and iron/manganese interaction in soda-lime-silic a glasses and cerium/manganese interaction in sodium borate glasses. The iron/ chromium and iron/manganese interaction fmishes already at high temperatures. In that case the amount of exchanged electrons can be calculated from stoichiometric considerations. The cerium/manganese couple shows a typical freezing-in behavior in sodium borate glass during cooling. The freezing-in temperature can be associated with the distance of the interacting ions.