Термодинамічні властивості пірофосфату кальцію Ca2P2O7: порівняння різних результатів та одержання нових даних

Abstract

In this work the analysis of applicability of Kellog-Kubaschewski method is conducted for establishment of isobaric heat capacity Ср of calcium pyrophosphate Ca2P2O7. On the basis of the analytical data, for low temperature modification of Ca2P2O7 certainly there are new thermodynamic properties. Divergence between the known results of isobaric heat capacity for the solid C-phase of calcium pyrophosphate Ca2P2O7 and got in this work is insignificant. In temperature range 298.15–600.00 K it does not exceed 1 %. With the increase of temperature of rejection % grows and arrives at a maximal value 2.233 % in a phase transit point at 1023.00 K. The values of other thermodynamic parameters, taken for comparison – change of enthalpy HT– H298, are characterized even less deviations from the known data. Value % grow to 1 % only at approaching to the temperature of structural transformation. With the purpose of comparison also took temperature dependences of isobaric heat capacity Ср and change of enthalpy for average and high temperature modifications of Ca2P2O7 (accordingly Band A-phases). Thus is established that at 1413 K (to the transit point of B- in A-phase) of rejection arrives at 3.299 %, and at 1631 K (to the overhead point of existence of A-phase) – 4.197 %. Interestingly to notice that at 1631 K begins melting of Ca2P2O7 and, in obedience to literary data, there is a jump of heat capacity is grows more than on 27 %. Such variation is not fixed a Kellog- Kubaschewski method, select in this work. Taking into account, that the most exact modern methods are characterized an error within the limits of 1–3 %, determination of isobaric heat capacity of Ca2P2O7 after a select method, at least to the first phase transition, it is possible to consider high-fidelity. In this connection, by the greatest exactness at determination of thermodynamic parameters (over 97 %) guilty characterized temperature interval 298.15–1023.00 K for which new results are got in this work. In particular, certainly values of Ср and HT–H298 for temperatures from the indicated range, but which are not resulted in literature. Are the proper values in addition, got for additional thermodynamic parameters – change of entropy ST– S298 and reduced of Gibbs energy ΦT, what are not in literary sources. Keywords: calcium pyrophosphate Ca2P2O7; thermodynamic properties; Kellog-Kubaschewski method.