ABSTRACT

The "B" type carbonate fluorapatites Ca10 x+u(PO4)6 x(CO3)xF2 x+2u, with 0 6 x 6 2 and u 6 x/2, were synthesized by a double decomposition method. The samples were characterized by X-ray diffraction and infrared spectroscopy. The heat of dissolution of these products in a phosphoric acid solution was measured by a C-80 SETARAM microcalorimeter. A thermochemical cycle was proposed and complementary processes were carried out in order to get the standard enthalpies of formation of these apatites. Estimation of the values of entropy of formation allowed the determination of standard Gibbs free energies of formation of these compounds. The results showed that incorporation of carbonate ions results in a decrease of the stability of the apatite structure.

Compounds

#	Formula	Name
1	FNa	sodium fluoride
2	Ca3O8P2	calcium phosphate
3	H5Na2O6P	disodium phosphate dihydrate
4	H3O4P	phosphoric acid
5	H2O	water

Datasets

The table above is generated from the ThermoML associated json file (link above). POMD and RXND refer to PureOrMixture and Reaction Datasets. The compound numbers are included in properties, variables, and phases, if specificied; the numbers refer to the table of compounds on the left.
Type	Compound-#	Property	Variable	Phase	Method	#Points
POMD	4 1 5	Molar enthalpy of solution, kJ/mol ; Liquid	Solvent: Mass fraction - 4; Liquid Mole fraction - 1; Liquid Temperature, K; Liquid Pressure, kPa; Liquid	Liquid	ISOPERIBOL	1
POMD	4 5 2	Molar enthalpy of solution, kJ/mol ; Liquid	Solvent: Mass fraction - 4; Liquid Mole fraction - 2; Liquid Temperature, K; Liquid Pressure, kPa; Liquid	Liquid	ISOPERIBOL	1
POMD	4 5 3	Molar enthalpy of solution, kJ/mol ; Liquid	Solvent: Mass fraction - 4; Liquid Mole fraction - 3; Liquid Temperature, K; Liquid Pressure, kPa; Liquid	Liquid	ISOPERIBOL	1

Thermodynamics Research Center / ThermoML | Journal of Chemical Thermodynamics

Standard enthalpy, entropy and Gibbs free energy of formation of "B" type carbonate fluorapatites

Zendah, H.[Houda], Khattech, I.[Ismail]

ABSTRACT