title: Calcium-deficient apatite synthesized by ammonia hydrolysis of dicalcium phosphate dihydrate: influence of temperature, time, and pressure.
abstract: In this work, calcium-deficient apatites (CDA) were synthesized by ammonia hydrolysis reaction of dicalcium phosphate dihydrate (DCPD; CaHPO4 x 2 H2O) to obtain biphasic calcium phosphates (BCP) without any extraionic substitution. The influence of three parameters was studied: temperature of the reaction (70 and 100 degrees C), time of the reaction (4 and 18 h), and the pressure (open and closed system). Experiments were made according to a factorial design method (FDM) allowing optimization of the number of samples as well as statistical analysis of results. Moreover, the influence of temperature (until 200 degrees C) was investigated. The crystal size of CDA was determined according to the Scherrer's formula and from Rietveld refinements taking the CDA anisotropy into account. The last method seems to be a reliable method to determine crystallite sizes of CDA, since crystallite sizes of CDA along <00l> and <hk0> directions were accessible. The results describe the hydroxyapatite % (HA%) in BCP by a first-order polynomial equation in the experimental area studied and the HA content was found to increase by raising time and temperature of the reaction. Moreover, the type of reaction system (open/closed vessel) appeared to have little influence on HA%.
authors: INSERM UMRS 791, Laboratoire d'Ingénierie Ostéoarticulaire et Dentaire, Univ Nantes, Faculté de Chirurgie Dentaire, BP 84215, F-44042, Nantes Cedex 01, France. laetitia.obadia@univ-nantes.fr
authors: Laetitia
authors: L
authors: Obadia
authors: Thierry
authors: T
authors: Rouillon
authors: Bruno
authors: B
authors: Bujoli
authors: Guy
authors: G
authors: Daculsi
authors: Jean Michel
authors: JM
authors: Bouler