Thermodynamics and diffusion of iron in homogeneous and phase separated sodium borosilicate melts

Voltammetric measurements were carried out at temperatures in the range of 600 to 1200 degrees C in both homogeneous and phase separated glass melts of different compositions in the Na2O-B2O3-SiO2 system doped with 0.5 mol% Fe2O3. At high temperatures, the current-potential curves were fairly similar to those recorded, e.g., in soda-lime-silica glasses. At temperatures below the immiscibility temperature T-C, peak splitting in the curves occurs, the two different states can be attributed to iron in the silica-rich and in the berate-rich phase. Peak splitting, however, also occurs up to temperatures about 250 degrees C higher than T-C. This behaviour is interpreted by a layer adjacent to the electrode formed by a boron-rich phase.