Fabrication, characterization, and properties of hydroxyapatite ceramics derived from cockle shell

Hydroxyapatite (HAp) powder was synthesized through a precipitation method using waste cockle shell as a calcium source. HAp powder had a single phase of Ca₅(PO₄)₃OH with a Ca/P ratio of 1.77. The crystals were rod-like, 80–110 nm long, and 20–30 nm wide. HAp ceramics sintered below 1350 °C in air resulted in ceramics with a stable HAp phase. The formation of β-tricalcium phosphate impaired the flexural strength of the specimen. The microhardness increased with sintering temperature due to the modification of density and porosity. The chemical solubility in acetic acid was related to density, porosity, and grain size. HAp ceramic sintered at 1250 °C provided appropriate properties for medical and dental applications. This ceramic had a grain size of 1.44 ± 0.37 µm, a density of 2.85 ± 0.01 g/cm³, a microhardness of 4.17 ± 2.37 GPa, a porosity of 10.3 ± 0.71%, a flexural strength of 46.13 ± 4.53 MPa, and a chemical solubility of 2.64 ± 0.10%.