Mechanical Characterization of Potassium and Hydroxyl Bearing Fluorapatite Bioceramics: A Brief Overview

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 Ca_10-xKx(PO₄)₆F_(2-2x)(OH)_x with 0 \(\le\) x \(\le\) 1 synthesized by the wet precipitation method, were found to be single-phase apatite 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\(^{\circ}\)C, indicated a partial decomposition of the apatite phase and its transformation to tricalcium phosphate \(\beta\)-Ca₃(PO₄)₂ at temperatures exceeding 750\(^{\circ}\)C. A relative density of the sintered samples achieved the highest value with x = 0.25 and reached about 95% after sintering at 1050\(^{\circ}\)C for 1 h. The microstructures of the sintered samples were 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 modulus, flexural strength and fracture toughness measurements. The overall trend of these parameters evolved comparable to the relative density, and the maximum values obtained from x = 0.25 were measured to be 96 MPa, 47 MPa and 1.14 MPa·m^1/2, respectively.