Evaluation of voltammetric redox potential for Fe3+/Fe2+ in silicate liquids

概要

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Redox potentials of Fe3+/Fe2+ in silicate liquids measured by voltammetry were evaluated by comparison with those obtained by other analytical methods. Differential pulse voltammetry was carried out for 20Na2O·80SiO2 and 18K2O·82SiO2 (mol%) melts doped with 0.5 or 3 wt% Fe2O3 and 15Na2O·9CaO·76SiO2 and 25CaO·16MgO·9Al2O3·50SiO2 melts doped with 1 wt% Fe2O3. Observed half wave potentials (E1/2) agreed with those of previous voltammetry experiments, however, systematically smaller than E1/2 calculated from redox ratios measured by wet chemistry and Mössbauer spectroscopy and redox potentials estimated from calorimetric data by about 0.1-0.3 V. The Fe3+/Fe2+ ratios calculated from the E1/2 by the voltammetry were always overestimated compared with those by other analytical methods. We could not explain the reason for discrepancy of the E1/2. It is expected that at least the discrepancy can not result from reduction of oxygen in working electrode, ohmic drop effect and difference between diffusivities of Fe2+ and Fe3+ in the liquids.