EFFECT OF BASICITY ON REDOX EQUILIBRIA IN SODIUM-SILICATE MELTS - AN IN-SITU ELECTROCHEMICAL INVESTIGATION

Redox ratios of chromium and antimony were directly measured at 1000 d egrees C in sodium silicate melts by electrochemical methods. The redo x ratios were found to increase while increasing the sodium oxide cont ent, i.e. the liquid basicity. It was shown that the logarithm of the redox ratio is a linear function of the logarithm of the sodium oxide activity. Our results differ systematically from those obtained on que nched samples. The results are discussed in the light of a thermodynam ic model considering activities of molecular species. We suggest that, when dissolved in silicate melts, multivalent ions form oxocomplexes which are not fully discrete species because non-bridging oxygens can intervene in their coordination sphere. We also concluded that there a re rapid exchanges of oxygen atoms between the oxocomplexes and the so lvent.