Thermal Behavior, Sintering and Mechanical Characterization of Multiple Ion-Substituted Hydroxyapatite Bioceramics

Abstract

Several trace elements such as Mg2+, Na+, K+, F−, Cl− are contained in biological apatite of natural bones. The presence of these elements in bones is indispensable for their calcification and mineralization. Their simultaneous insertion in the apatite framework with preserved structure was our aim. Therefore, calcium hydroxyapatite (HAp) biomaterials doped with the aforementioned ions was the subject of the present study. Three formulations of ion-substituted HAp powders were prepared via a wet-chemical precipitation method. Analysis and characterization by several techniques proved that the obtained powders were of apatitic nature. Although stoichiometry was slightly weaker, multiple ion-substitutions lead to stable structures. When sintering, calcined powders at 500 °C for 1 h were uniaxially isostatically cold compacted into pellets. These pellets were pressurelessly sintered in a temperature range of 900–1250 °C. The maximum 95% densification value was obtained with the samples sintered at temperature 1150 °C for 1 h. A secondary phase of β-Ca3(PO4)2 appeared at 730 °C related to partial decomposition of the apatitic phase. The sintered materials were mechanically characterized by measurements of compressive and flexural strengths, fracture toughness, Young’s modulus and microhardness and the maximum values were obtained as 154 MPa, 60 MPa, 1.55 MPa·m1/2, 151 GPa and 600 Hv, respectively.