Formation mechanism of nano-hardystonite powder prepared by mechanochemical synthesis

•Utilization of mechanochemical synthesis to fabricate nano-hardystonite.•Optimised condition of 20 h milling followed by sintering at 900 °C.•Findings on the chemical reactions during hardystonite formation.•Application of a two-step sintering method to prepare bulk hardystonite.•Bulk hardystonite compressive strength (121 ± 2 MPa) and elastic modulus (27 ± 4 GPa) were measured.

Hardystonite is currently recognized as a biocompatible bio-ceramic material for a range of medical applications. In this study, pure nano-crystalline hardystonite powder was prepared by mechanochemical synthesis of calcium carbonate, zinc oxide and silicate oxide in a planetary ball mill followed by sintering. A range of techniques including X-ray diffraction (XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM) were applied to fully characterize the obtained powders. The effect of time and sintering temperature on the formation mechanism of nano-hardystonite was studied. It was found that pure nano-crystalline hardystonite powder formation occurred following 20 h of milling and subsequent sintering at 900 °C for 3 h. The measured crystallite and agglomerate particle size were found to be 28 ± 2 and 191 ± 3 nm, respectively. The two-step sintering processing was also applied for the preparation of bulk hardystonite. The compressive strength and elastic modulus of bulk hardystonite with 75.5 ± 3% relative density were approximately 121 ± 2 MPa and 27 ± 4 GPa, respectively.

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