PHASE STABILITY AND MORPHOLOGICAL EVOLUTION OF HYDROXYAPATITE PREPARED AT DIFFERENT BALL-MILLING TIME

Abstract

Eggshells are readily available organic wastes used as calcium precursors in the form of calcium oxide for producing Hydroxyapatite (HA). However, limited research has been reported on the potential of eggshell-derived calcium precursors in calcium carbonate (CaCO₃). This study used CaCO₃ from calcined eggshell waste as a sustainable calcium precursor to synthesise HA by combining mechanochemical activation and a heat treatment regime at 800 °C. The effects of varying ball milling duration (5, 6, and 7 hours) at the rotational speed of 550 rpm were explored.  It was observed that all synthesised powders exhibited a high degree of HA crystallinity with a minor appearance of β-TCP as the milling time increased from 6 to 7 hours. Better crystallite size with increased milling times was observed with 16.15nm, 12.767nm and 12.237nm for 5,6 and 7 hours of ball-milling time, respectively. A similar trend was also exhibited in morphological analysis whereby the agglomeration of particles along with average particle size decreases with milling times. Besides that, the Ca/P ratio obtained in all synthesised powders closely resembles the Ca/P ratio of pure HA at 1.67. Thus, CaCO₃ from calcined eggshell waste has been successfully employed as a sustainable calcium precursor in producing eggshell-derived HA.