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

Redox potentials of Fe3+/Fe2+ in silicate liquids measured by voltammetry were evaluated by comparison with those obtained by other analyitical methods. Differential pulse voltammetry was carried out for 20Na(2)O center dot 80SiO(2) and 18K(2)O center dot 82SiO(2) (mol%) melts doped with 0.5 or 3 wt% Fe2O3 and 15Na(2)O center dot 9CaO center dot 76SiO(2) and 25CaO center dot 16MgO center dot 9Al(2)O(3)center dot 50SiO(2) melts doped with 1 wt% Fe2O3. Observed half wave potentials (E-1/2) agreed with those of previous voltammetry experiments. however, systematically smaller than E-1/2 calculated from redox ratios measured by wet chemistry and Mossbauer spectroscopy and redox potentials estimated from calorimetric data by about 0.1-0.3 V. The Fe3+/Fe2+ ratios calculated from the E-1/2 by the voltammetry were always overestimated compared with those by other analytical methods. We could not explain the reason for discrepancy of file E-1/2. It is expected that at least the discrepancy call not result from reduction of oxygen in working electrode. ohmic drop effect and difference between diffusivities of Fe2+ and Fe3+ in the liquids. (C) 2009 The Ceramic Society of Japan All rights reserved