Measurement of the effects of temperature and partial pressure of oxygen on the oxidation states of europium in silicate glasses

The techniques of electron paramagnetic resonance (EPR) were used to measure the concentration ratio of Eu²⁺ to Eu³⁺ in quenched CaMgSi₂O₆, Ca₃Si₃O₁₂, and CaAl₂Si₂O₈ liquids as functions of partial pressure of oxygen and temperature. The redox equilibrium of the Eu ions was described by the reaction 4Eu³⁺ + 20^2? = 4Eu²⁺ + O₂. The reduction of Eu³⁺ to Eu²⁺ was endothermic, and for CaMgSi₂O₆ and Ca₃Al₂Si₃O₁₂ liquids the mean value of ΔH⁰ and the standard deviation from that mean were 25 ± 7 kcal/mole.The magnitude of the Eu anomaly in the distribution coefficients is discussed in terms of the compositions of the solid and liquid phases.