Sintering of potassium doped hydroxy-fluorapatite bioceramics

Abstract

The present study describes the influence of potassium and hydroxyl substitutions on the structural, thermal and mechanical properties of fluorapatite bioceramics. A set of non-stoichiometric ion-substituted compounds, with a chemical formula of Ca10−x Kx (PO4 )6 F(2−2x) (OH)x with 0 ≤ x ≤ 1 synthesized by the wet precipitation method, were found to be single-phase apatites crystallizing in the hexagonal P63 /m space group. The structural parameters, as well as the crystallite sizes, increased accordingly to the amount of added dopant-ions. The thermal behavior of these compounds, studied within the temperature range 500–1200◦ C, indicated a partial decomposition of the apatitic phase and its transformation to tricalcium phosphate β-Ca3 (PO4 )2 at temperatures exceeding 750◦ C. A relative density of the sintered samples achieved the highest value with x = 0.25 and reached about 95% after sintering at 1050◦ C for 1 h. The microstructures of the sintered samples were of a trans-granular aspect and experienced an increase in the radius of their pores as x increased. The prepared bioceramic materials were mechanically characterized by means of Young’s modu-lus, flexural strength and fracture toughness measurements. The overall trend of these parameters evolved comparably to the relative density, and the maximum values obtained for x = 0.25 were measured to be 96 MPa, 47 MPa and 1.14 MPa·m1/2, respectively.