High-temperature electrochemical study of Na2O-MoO3 melts

Physical chemistry of the Na2O-MoO3 system was investigated using a high-te mperature electrochemical cell with Na, p-alumina as the solid electrolyte. The reference electrode was a solid mixture of tungsten, tungsten sulfide and sodium sulfide. The cell may be expressed as the following: W(s),WS2(s) / Na+ / O-2(g), Pt(s) Na2S(s) / beta -alumina / Na2O-MoO3 melt The activity of Na2O in the Na2O-MoO3 melt in the composition range from 50 .87 to 92.18 mol% MoO3 and temperatures from 890 to 1230 K was determined u sing this cell. Partial molar enthalpies of mixing for Na2O in the melt wer e evaluated from the temperature dependence of the activity data using the Gibbs-Helmhotz equation. The values agree with those reported in the litera ture from calorimetric measurements. The activity of MoO3 in the melt as a function of the melt composition at various temperatures was also determine d using the Gibbs-Duhem equation and the Na2O-MoO3 phase diagram. (C) 2001 Elsevier Science B.V. All rights reserved.