Search

The enthalpies of the reactions of double rare-earth and barium cobaltites Ln2BaCOO5 (Ln = Nd, Gd, Dy, Ho) and metallic dysprosium with 1 M hydrochloric acid are measured at 298.15 K using precision calorimetric equipment. The standard enthalpies of formation of Ln2BaCoO5 from simple components and binary oxides were calculated from the obtained results and reliable literature data.

The thermodynamic properties and oxygen stoichiometry of Ba2Cu3O5 + δ are studied by means of the electromotive force (EMF) with a fluoride electrolyte, dissolution calorimetry, and thermogravimetry. It is shown that the temperature dependence of the Gibbs energy of the formation of barium cuprate from simple oxides and oxygen in the temperature range of 860–1120 K can be described by the polynomial Δf, oxG∘(Ba2Cu3O5 + δ) ± 0.1 (kJ/mol) = −291.78 + 1.127T − 0.13207 TlnT (kJ/mol).

The enthalpies of reactions of Sm1 + xBa2 − xCu3Oy substitution solid solutions (x = 0, 0.1, 0.2, 0.3, 0.7, and 0.8) with 1.07 N HCl were measured at 298.15 K in a hermetic isothermic-shell swinging calorimeter. The results and the literature data were used to calculate the standard enthalpies of their formation from simple substances and binary oxides (ΔfH298.15o and ΔoxH298.15o). The dependence of the enthalpy of formation on the degree of samarium substitution for barium was obtained.

The enthalpies of reactions of substitution solid solutions Pr1 + xBa2 − xCu3Oy, where x = 0, 0.2, 0.4, 0.6, and 0.9, with 1.07 N HCl were measured at 298.15 K in a hermetic swinging isothermic-shell calorimeter. The results and the literature data were used to calculate the standard enthalpies of formation of solid solutions from the elements and oxides. The dependence of the enthalpy of solid solution formation on the degree of praseodymium substitution for barium (x) was revealed.

The enthalpies of solution of praseodymium tribromide and triiodide in water were measured at 298.15 K in a hermetic isothermic-shell swinging calorimeter. The data obtained and the Δf H° (Pr3+, sln, ∞H2O, 298 K) value found earlier were used to calculate the enthalpies of formation of three praseodymium halides (PrCl3, PrBr3, and PrI3) in the crystalline state and aqueous solution.

The enthalpy of reaction between praseodymium metal and 1.07 n HCl and the enthalpy of solution of praseodymium trichloride in 1.07 n HCl and water were measured in a swinging isoperibol calorimeter at 298.15 K. The results were used to calculate the enthalpy of formation of the praseodymium ion in the state of an infinitely dilute aqueous solution, ΔfH°298.15 Pr3+(sln, ∞H2O) = −687.8 ± 1.7 kJ/mol.

The thermodynamic properties of the Ln2BaO4 phases (Ln = Dy, Ho, Sm) were studied by the electromotive force method with a fluoride electrolyte (890–1180 K), solution calorimetry in 1.07 N hydrochloric acid at 298.15 K, and differential scanning calorimetry (298–860 K). The experimental data were jointly processed, and the thermodynamic functions of the compounds over the temperature range 298–1200 K were calculated.

The enthalpy of reaction of metallic calcium with perchloric acid was measured for the first time in a sealed swinging calorimeter equipped with an isothermal shell. Standard enthalpies of formation of calcium ion in an infinitely diluted aqueous solution (−542.8 ± 1.0 kJ/mol) and calcium chloride in crystal state (−794.9 ± 1.0 kJ/mol) were calculated according to the results obtained with the use of published data.

Thermoanalysis (TG-DSC) of the pure compound Ba2Cu3O5+δ (023) has been carried out at oxygen pressures of 0.21 and 1 atm in the temperature range 25–970°C. It was shown that 5.5 823°C at 0.21 atm O2; > 890°C at 1 atm O2) appeared. The liquid phase transition took place at temperatures higher than 860°C (0.21 atm) and 910°C (1 atm).