Thermodynamic calculation of the formation of ceramic coatings based on dicalcium phosphate dihydrate and octacalcium phosphate

This research is focused on preliminary calculations of the thermodynamic model and total Gibbs energy for ceramic coatings based on dicalcium phosphate dihydrate (CaHPO$_4$ $\cdot$ 2H$_2$O) and octacalcium phosphate (Ca$_8$H$_2$(PO$_4$)$_6$ $\cdot$ 5H$_2$O) obtained by chemical modification of ceramics based on $\alpha$-tricalcium phosphate (Ca$_3$(PO$_4$)$_2$). The formation of thermodynamically favorable calcium phosphate (CP) phases during the formation of coatings is shown. The calculations were carried out using the Medusa software. Solutions of sodium acetate (CH$_3$COONa) and phosphoric acid (H$_3$PO$_4$) were used as initial components of the system. According to the calculations, at a pH value of 5.1 and a concentration of pH = 5.1 ions = 10$^{-2}$ M and PO$_4^-$ = 0.45 M, a coating based on DCPD is formed, and at a pH value of 9 and a concentration of pH = 9 ions = 10$^{-3}$ M – phase OCP.