Magnesium‐substituted hydroxyapatite ceramics

The effect of the addition of magnesium (up to 10 wt%, expressed as MgO) on the phase composition, the microstructure and the mechanical properties of hydroxyapatite‐based ceramics (HA) was studied by X‐ray powder diffraction, infrared spectroscopy, scanning electron microscopy, and mechanical testing. Doping with magnesium did not change the crystal lattice of HA but, due to an isomorphous substitution of Mg2+for Ca2+, it caused a decrease in the average grain size, an increase of microporosity, a removal of the texture, and the formation of a weak intergranular boundary. The transcrystallite fracture pattern of pure HA was changed to a predominantly intercrystallite one. This resulted in a decrease in density (down to 2.93 g cm‐3), in microhardness (down to 400 MPa), in compressive strength (down to 190 MPa) and in improved plastic properties of the material (increasing the fracture toughnessK1C up to 2.7 MPa m1/2, close to that of the bone). It is interesting that theK1C increase could be only observed for a small concentration of additives (up to 1 wt%), i.e. close to the Mg concentration in natural bone mineral.