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 (p0 =0.1 MPa) thermodynamic functions Cp,m-bar /R,Δ0THm-bar /RT,Δ0TSm-bar /R,andΦm-bar =Δ0TSm-bar -Δ0THm-bar /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