Synthése et thermochimie de phosphates au cadmium: Partie I: Cas du phosphate tricadmique et de la chlorapatite cadmiée

Tricadmium phosphate Cd3(PO4)2 (TriCd) and cadmium chlorapatite Cd10(PO4)6Cl2 (CdClap) were prepared by dry chemistry method. They were characterized by X-ray diffraction, IR spectroscopy and chemical analysis. Using an isoperibol calorimeter, the heat of solution of these products in 9% weight nitric acid solution were determined. They are (−147,3±2,1) kJ mol−1 and (−261,6±1,1) kJ mol−1 for TriCd and CdClap, respectively. Combining these results with the enthalpies of formation of [Cd(NO3)2, 4H2O], H3PO4aq, HClaq and H2O and their enthalpies of solution in the same solvent, leads to the standard enthalpies of formation of these Cd-phosphates. These quantities are: −2626 kJ mol−1 for TriCd and −8463 kJ mol−1 for CdClap.