Redox equilibria and kinetics of iron in a borosilicate glass-forming melt

Abstract

The redox element that is most often prevalent in glass-forming melts is iron. Fundamental equilibrium and kinetic properties pertaining to the oxidation-reduction reactions of iron in glass melts are thus of prime importance in understanding the basic chemistry of redox species in such systems. A comprehensive study of the redox equilibria and kinetics of iron, Fe(III)-Fe(II)-Fe(0), in the borosilicate glass melt SRL131 (57.9 wt.% SiO 2, 1.0% TiO 2, 0.5% ZrO 2, 14.7% B 2O 3, 0.5% La 2O 3, 2.0% MgO, 17.7% Na 2O, and 5.7% Li 2O) has been completed. Composition SRL131, Savannah River Laboratory glass frit 131, is a typical waste form under consideration for the immobilization of nuclear waste and has also been widely used as a reference melt for the characterization of glasses. The iron redox equilibria have been determined as a function of the melt temperature, imposed oxygen fugacity, and total iron content of the melt. Iron redox kinetics in a melt, whereby a system initially at equilibrium is perturbed by a change in imposed oxygen fugacity so that the kinetics of equilibrium re-establishment can be monitored, have been measured as a function of the melt temperature and total iron content of the melt. Such kinetic information has been related to the diffusion of oxygen through the melt.