High temperature stabilities of interoxides in the system Fe–Sb–O and their comparison with the interoxides in other M–Sb–O (M=Cr, Ni or Co) systems

Abstract

An isothermal section of the phase diagram of the system Fe–Sb–O at 873 K was established by isothermal equilibration and XRD analyses of quenched samples. Two ternary oxides namely FeSb 2O 4 and FeSbO 4 were identified. Making use of the phase diagram, the oxygen potentials of the ternary phases were measured by employing the following solid electrolyte based galvanic cells: (I) Chromel, Mo, Sb, Fe 3O 4, FeSb 2O 4∣15 CSZ∣NiO, Ni, Mo, Chromel (II) Pt, Fe 3O 4, FeSb 2O 4, FeSbO 4∣15 CSZ∣air (P O 2 =0.21 atm), Pt (III) Pt, FeSb 2O 4, FeSbO 4, Sb 2O 3∣15 CSZ∣air (P O 2 =0.21 atm), Pt where 15 CSZ stands for ZrO 2 stabilized by 15 mol% CaO. The least-squares regression analyses of the emfs of the galvanic cells I, II and III (split into two ranges) measured over the temperature ranges 771–911, 771–921 and 787–981 K, respectively, can be represented by the expressions E I±0.39 (mV)=152.8–0.04728 T ( K) E II±0.22 (mV)=1010.0–0.4172 T ( K) E IIIA±0.46 (mV)=870.1–0.3665 T ( K) E IIIB±0.31 (mV)=809.3–0.2992 T ( K) These emf expressions were used to derive the standard Gibbs’ energies of formation of FeSb 2O 4 and FeSbO 4 and are given by ΔG f o (FeSb 2O 4)±3.5 (kJ mol −1)=−1068.7+0.3561 T ( K) ΔG f o (FeSbO 4)±5.5 (kJ mol −1)=−976.9+0.3289 T ( K) The emf of the cell III exhibited a break corresponding to the liquidus temperature of Sb 2O 3. The cell III was used to assess the internal consistency of Δ G f o (FeSbO 4) derived from cell II. The consistency of Δ G f o data for these two interoxides with the relevant tie-lines in Fe–Sb–O system is highlighted. Comparison of iron interoxide stabilities with those of six other interoxides in the systems M–Sb–O where M is Cr, Co or Ni reported earlier in the literature revealed FeSb 2O 4 to be the most stable interoxide with respect to the equilibrium oxygen dissociation pressure in the corresponding set of coexisting phases. Hence, this interoxide is proposed to substitute Sb 2O 3 in the auxiliary neutron source of liquid metal cooled fast breeder reactors subject to meeting other physics requirements.