Thermodynamic study of MgO–Sb2O3 system and the stability functions of magnesium antimonite

• Standard Gibbs free energy of formation of MgSb2O4 was accurately measured.
• New set of data on ΔfG° of magnesium antimonite was determined by the EMF method.
• Galvanic cells based on yttria stabilized zirconia solid electrolyte were employed.
• Activity of liquid antimony in the MgO–MgSb2O4 saturation was calculated.

In this study, the standard Gibbs free energy of formation of MgSb2O4 has been determined by means of the solid-oxide electrolyte EMF technique. A pure-oxygen reference electrode was applied for the first time to this system in an oxygen concentration cell. The EMF values, temperature and the prevailing pressure of the following galvanic cell were measured:(-)Pt,Re,Sb(l),MgO(s),MgSb2O4(s)|YSZ|O2(g),Pt(+).(-)Pt,Re,Sb(l),MgO(s),MgSb2O4(s)|YSZ|O2(g),Pt(+).The standard Gibbs free energy of the virtual cell reaction 2Sb(l)+3/2O2(g)+MgO(s)=MgSb2O4(s)2Sb(l)+3/2O2(g)+MgO(s)=MgSb2O4(s) was determined to be:ΔrG°/(kJ·mol-1)±2.97=-734.96+0.2645T/K(906≤T/K≤1148).The standard Gibbs free energy of formation of solid MgSb2O4 from its pure component oxides Sb2O3(l)+MgO(s)=MgSb2O4(s)Sb2O3(l)+MgO(s)=MgSb2O4(s) was determined to be:ΔfG°MgSb2O4/(kJ·mol-1)±3.00=-52.75+0.0253T/K(929≤T/K≤1148).The standard Gibbs free energy of formation of solid MgSb2O4 from the elements Mg(l)+2Sb(l)+2O2(g)=MgSb2O4(s)Mg(l)+2Sb(l)+2O2(g)=MgSb2O4(s) was determined to be:Δf′G°MgSb2O4/(kJ·mol-1)±18.2=-1392+0.4055T/K(973≤T/K≤1148).