EPR and voltammetric studies of iron-containing mixed alkali glasses with the basic composition xNa₂O · (16-x)Κ₂O * 10CaO * 74SiO₂

Abstract

Mixed soda-potassium-lime glasses containing iron oxide in a concentration ränge of 0.1 to 2 m o l % were studied by means of EPR spectroscopy and voltammetry. At low iron concentrations a one-step reduction of Fe³ to Fe² was observed. The values of the Standard reaction enthalpy, ΔH⁰, and of the Standard reaction entropy, ΔS⁰, calculated from the temperature dependence of the Standard potentials show maxima if sodium and potassium concentrations are approximately equal. EPR spectra of all glasses investigated show two paramagnetic signals at g = 2.0 and g = 4.3. The ratio of the peak intensities, I₂.₀ /I₄.₃, increases with the Square of the total iron concentration. Here, the intensity of the g = 4.3 peak increases with increasing Na₂O concentration; the behaviour of the mixed alkali glasses, however, cannot be explained as an additive effect.