Hydroxyapatite synthesized from oyster shell powders by ball milling and heat treatment

Enormous quantities of shells accumulate from oyster farms along coastlines in many areas of the world. The wide availability and the low cost of oyster shells, along with their biological–natural origin are highly attractive properties in the preparation of hydroxyapatite (HA) powders for biomedical application. Chemical and microstructural analysis has shown that oyster shells are predominantly composed of calcium carbonate with rare impurities. In this investigation, solid state reactions between oyster shell powders (calcite polymorph of CaCO3) and calcium pyrophosphate (Ca2P2O7) or dicalcium phosphate dihydrate (CaHPO42H2O, DCPD) were performed through ball milling and subsequently heat treatment. The ball milling and heat treatment of Ca2P2O7 and oyster shell powders in air atmosphere, produced mainly HA with a small quantity of β-tricalcium phosphate (β-TCP) as a byproduct. However, oyster shell powder mixed with DCPD and milled for 5 h followed by heat-treatment at 1000 °C for 1 h resulted in pure HA, retaining none of the original materials.