Structural and Mechanical Behavior of Mechanochemically Synthesized Nanocrystalline Hydroxyapatite from Mercenaria Clam Shells

The aim of the present investigation is to develop mechanochemically synthesized nano-crystalline hydroxyapatite (nHAp) bioceramics using clam seashells and phosphoric acid by varying the CaO:H3PO4 acid at different wt% ratios, i.e. 1:0.75, 1:1.0, 1:1.25, 1:1.5 and 1:1.75. The synthesized powders were characterized using X- ray diffraction ( XRD), scanning electron microscope and high resolution transmission electron microscopy. XRD results showed that the average crystallite size of the powder varies from 54 to 69 nm with enhancement in its crystallinity from 85 to 96%. An attempt was laid to access the mechanical behavior of nHAp through indentation at the micron scale. Microindentation derived properties, viz. microhardness, fracture toughness, brittleness index and fracture energy showed significant variation with CaO:H3PO4 mixing ratio due to the evolution of HAp and other calcium phosphate based phase(s). The fracture behavior illustrated a considerable improvement with the variation in CaO:H3PO4 mixing ratio.