title: Calorimetry investigations of milled α-tricalcium phosphate (α-TCP) powders to determine the formation enthalpies of α-TCP and X-ray amorphous tricalcium phosphate.
abstract: One α-tricalcium phosphate (α-TCP) powder was either calcined at 500°C to obtain fully crystalline α-TCP or milled for different durations to obtain α-TCP powders containing various amounts of X-ray amorphous tricalcium phosphate (ATCP). These powders containing between 0 and 71wt.% ATCP and up to 2.0±0.1wt.% β-TCP as minor phase were then hydrated in 0.1M Na2HPO4 aqueous solution and the resulting heat flows were measured by isothermal calorimetry. Additionally, the evolution of the phase composition during hydration was determined by in situ XRD combined with the G-factor method, an external standard method which facilitates the indirect quantification of amorphous phases. Maximum ATCP hydration was reached after about 1h, while that of crystalline α-TCP hydration occurred between 4 and 11h, depending on the ATCP content. An enthalpy of formation of -4065±6kJ/mol (T=23°C) was calculated for ATCP (Ca3(PO4)2), while for crystalline α-TCP (α-Ca3(PO4)2) a value of -4113±6kJ/mol (T=23°C) was determined.
authors.affiliation: GeoZentrum Nordbayern - Mineralogy, Friedrich-Alexander-University of Erlangen-Nuremberg, Schlossgarten 5, 91054 Erlangen, Germany. Electronic address: katrin.hurle@fau.de.
authors.forename: Katrin
authors.initials: K
authors.lastname: Hurle
authors.affiliation: GeoZentrum Nordbayern - Mineralogy, Friedrich-Alexander-University of Erlangen-Nuremberg, Schlossgarten 5, 91054 Erlangen, Germany.
authors.forename: Juergen
authors.initials: J
authors.lastname: Neubauer
authors.affiliation: RMS Foundation, Bischmattstrasse 12, CH-2544 Bettlach, Switzerland.
authors.forename: Marc
authors.initials: M
authors.lastname: Bohner
authors.affiliation: RMS Foundation, Bischmattstrasse 12, CH-2544 Bettlach, Switzerland.
authors.forename: Nicola
authors.initials: N
authors.lastname: Doebelin
authors.affiliation: GeoZentrum Nordbayern - Mineralogy, Friedrich-Alexander-University of Erlangen-Nuremberg, Schlossgarten 5, 91054 Erlangen, Germany.
authors.forename: Friedlinde
authors.initials: F
authors.lastname: Goetz-Neunhoeffer
mesh_terms: D018786:Bone Substitutes / Q000737:chemistry*; D002130:Calcium Phosphates / Q000737:chemistry*; D002151:Calorimetry / Q000379:methods*; D003460:Crystallization / Q000379:methods*; D008422:Materials Testing / Q000379:methods*; D011208:Powders; D013814:Thermal Conductivity; D013816:Thermodynamics; D014867:Water / Q000737:chemistry*; D014961:X-Ray Diffraction
chemical_list: D018786:Bone Substitutes; D002130:Calcium Phosphates; D011208:Powders; C485828:alpha-tricalcium phosphate; D014867:Water
keywords: Amorphization; CDHA; Calcium phosphate cement; Heat flow calculation; Isothermal calorimetry