Stoichiometry and particle morphology effects on the aptitude to compaction of apatitic structure powders

Apatitic calcium phosphates powders with Ca/P molar ratio of 1.5 to 1.8 were synthesized at 25 °C using the neutralization method. These powders, differing by stoichiometry and particle morphology, were compacted in similar conditions. For a similar morphology of particles, compacts of the non-stoichiometric powders have better cohesion than those of the stoichiometric hydroxyapatite (Ca10(PO4)6(OH)2: Ca/P = 1.67). The lacunar structure, with deficiency of calcium (Ca10 − x (HPO4)x(PO4)6 − x(OH)2 − x: 1.5 < Ca/P < 1.67), seems to favour the densification process and cohesion between particles during the compaction. The better tensile strength (0.79 MPa) was obtained for the powder with the lowest atomic ratio (Ca/P = 1.5, x = 1). The apatite powder (Ca/P = 1.78), which has a smooth and porous structure, presented the best transmission load ratio (95.5%), the lowest die-wall friction (μ = 0.1) and the highest strength (3.12 MPa). These results show the importance of chemical composition and morphological properties of synthesized particles in the development of better hydroxyapatite powders for the compaction process.