Thermodynamic properties of trizirconium tetraphosphate

The heat capacity measurements of the crystalline trizirconium tetraphosphate were carried out in a low-temperature adiabatic vacuum calorimeter between T = (7 and 350) K and in dynamic calorimeter between T = (330 and 640) K. The experimental data were used to calculate the standard (p∘ = 0.1 MPa) thermodynamic functions Cp,m∘/R,Δ0THm∘/RT,Δ0TSm∘/R,andΦm∘=Δ0TSm∘-Δ0THm∘/T (where R is the universal gas constant) in the range T → (0 to 640) K. The fractal dimension Dfr for the crystalline phosphate Zr3(PO4)4 between T = (20 and 40) K was evaluated. From hydrofluoric acid solution microcalorimetry, the enthalpy of solution of Zr3(PO4)4 at T = 298.15 K was determined and the standard molar enthalpy of formation was derived. By combining the data obtained by the two techniques, the standard molar Gibbs function of formation of Zr3(PO4)4 at T = 298.15 K was calculated.