Determination of standard Gibbs free energy of formation for Ca2P2O7 and Ca(PO3)2 from solid-state EMF measurements using yttria stabilised zirconia as solid electrolyte

Determination of standard Gibbs free energy of formation for CaKPO4, CaK4(PO4)2, CaK2P2O7, and Ca10K(PO4)7 from solid-state e.m.f. measurements using yttria stabilised zirconia as solid electrolyte

“…four equilibria and four species with unknown thermodynamic data. The discussion about the D f G°(Ni 3 P) temperature function has previously been addressed by Sandströ m et al [4].…”

“…Besides CaO and K 4 The discussion regarding the galvanic cell technique and the involvement of the auxiliary solid couple, Ni/Ni 3 P, has previously been addressed by Sandströ m et al [4]. The oxygen pressures obtained in these equilibria can be determined by e.m.f.…”

“…), Fe 2 O 3 (Fischer Scientific, Pittsburgh, PA), Ni (Merck) and Ni 2 P (Aldrich). CaK 2 P 2 O 7 was synthesised by mixing Ca(PO 3 ) 2 and K 2 CO 3 in equimolar amounts and keeping the mixture at 1073 K for $18 h. CaKPO 4 was synthesised by mixing Ca 2 P 2 O 7 and K 2 CO 3 in equimolar amounts and maintaining the mixture at 1273 K for $18 h. CaK 4 (PO 4 ) 2 was synthesised by mixing Ca(PO 3 ) 2 and K 2 CO 3 in a 1:2 ratio, heated to 1273 K and kept at that temperature for $18 h. K 4 P 2 O 7 was synthesised by dehydrating K 2 HPO 4 at 673 K. Ca 3 (PO 4 ) 2 was used as starting material in equilibrium (IV) and its synthesis has been described by Sandströ m et al [4]. The syntheses of CaO, Ca(PO 3 ) 2 , Ca 2 P 2 O 7 , and the reference system Fe/'FeO' have also been described by Sandströ m et al [4].…”

“…However, reliable thermodynamic data for ternary phases in this system are lacking. Work is now being carried out at our department to structurally characterise and to determine stabilities of a number of phases in the CaO-K 2 O-P 2 O 5 system [1][2][3][4][5][6]. Recently, solid state e.m.f.…”

“…Recently, solid state e.m.f. measurements were carried out to determine Gibbs free energies in the subsystem CaO-P 2 O 5 [4]. The present work was undertaken to determine thermodynamic stabilities of a number of ternary phases using the solid electrolyte galvanic cell technique.…”