Test and calibration processes for the differential reaction calorimeter (DRC): Application: Dissolution of calcium fluorapatite in the hydrochloric acid

• Modification of a DRC Setaram calorimeter in order to have higher sensitivity.
• Calorimeter's calibration was done by electrical effects and a statistical treatment was performed to adjust the calibration curve coefficients.
• Performance of calorimeter tested by dissolution measurement of the “THAM” in HCl (0.1 mol kg−1).
• Dissolution molar enthalpies of calcium fluorapatite in HCl (0.1 M; 0.5 M; 1.0 M; 1.5 M; 2.0 M) at 298 K.
• Dissolution molar enthalpy of calcium fluorapatite in water at 298 K.

Changes were performed on the apparatus of the differential reaction calorimeter (DRC) in order to get higher sensitivity. The performance of this simple instrument was tested by measuring the enthalpy of dissolution of the trihydroxymethyl aminomethane, (HOCH2)3CNH2, or “THAM” in 240 g of 0.1 mol L−1 hydrochloric acid at 298 K. We used the joule effect to calibrate the DRC and a statistical treatment to adjust the coefficients of calibration curves.DRC was also used to achieve the dissolution of the synthesized calcium fluorapatite, Ca10(PO4)6F2, in hydrochloric acid for different concentrations at 298 K. Two solution mechanisms were suggested for different pH ranges and therefore the enthalpy of dissolution of Ca10(PO4)6F2 in pure water was deduced.