Effect of AlF3, CaF2 and MgF2 on hot-pressed hydroxyapatite–nanophase alpha-alumina composites

Nanophase alpha-alumina and hydroxyapatite composites (with and without 5 wt% AlF3, CaF2 or MgF2, added separately) were hot pressed at 1100 °C and 1200 °C to investigate their mechanical properties and phase stability. Hydroxyapatite slightly decomposed to tri-calcium-phosphate when there was no F− present. With the addition of AlF3, CaF2 or MgF2 into the composite, it improved its thermal stability and mechanical properties. Substitution of OH− by F− ions in hydroxyapatite was verified by the change in hydroxyapatite's hexagonal lattice parameters and unit cell volume. A fracture toughness of 2.8 MPa m and μ-hardness of 8.25 GPa were calculated for the composite containing CaF2 after the hot pressing at 1200 °C.