Title: Measurement of the Activity of Fe<SUB>T</SUB>O in Na<SUB>2</SUB>O&ndash;CaO&ndash;SiO<SUB>2</SUB>&ndash;Fe<SUB>T</SUB>O and CaO&ndash;CaCl<SUB>2</SUB>&ndash;Fe<SUB>T</SUB>O Melts by the EMP Method
Abstract:The activities of FeTO in the Na2O–CaO–SiO2–FeTO and CaO–CaCl2–FeTO fluxes have been calculated from the EMF values of the following cells determined in the temperature range from 1273 to 1573 K.Fe(pu...The activities of FeTO in the Na2O–CaO–SiO2–FeTO and CaO–CaCl2–FeTO fluxes have been calculated from the EMF values of the following cells determined in the temperature range from 1273 to 1573 K.Fe(pure solid)/Na2O–CaO–SiO2–FeTO//ZrO2/O2, PtandFe(pure solid)/CaO–CaCl2–FeTO//ZrO2/O2, Pt.ZrO2 solid electrolyte stabilized with CaO or MgO was used as the reference electrode.Results obtained are summarized as follows:(1) The activity coefficient of FeTO(γFeTO°) in the Na2O–SiO2–FeTO flux increases with an increase in the Na2O/SiO2 ratio. The values of γFeTO° obtained at 1473 K for the fluxes with 1.5, 1.0 and 0.5 in the molar ratio of Na2O/SiO2 were 7.5, 2.3 and 0.5, respectively. Substitution of Na2O by CaO significantly reduces γFeTO° in a higher basicity region.(2) In the case of the CaO–CaCl2–FeTO flux with the concentration of FeTO less than 1%, γFeTO° decreases with increasing CaO content at temperatures from 1273 to 1573 K. γFeTO° of the CaO–CaCl2–FeTO flux containing 1 mol%FeTO was 12.6, 5.6, 4.0 and 1.6, when the molar ratio of CaO/CaCl2 was 5/95, 1/9, 1/4 and 3/7, respectively.(3) Thermodynamic quantities for the mixing of FeTO in the CaO–CaCl2 fluxes were calculated. Gibbs’s partial molar free energies for the mixing of FeTO(ΔHFeTOM) were 33 to 172 kJ/mol at temperatures from 1273 to 1573 K. These values are in good agreement with the values from 66 to 276 kJ/mol determined by Kay and Mitchell for the CaO–CaF2–FeTO fluxes at temperatures from 1673 to 1723 K.Read More