Spark plasma sintering of graphene reinforced hydroxyapatite composites

Hydroxyapatite (prepared from eggshell)/graphene (HAP/GNPs) composites were prepared by spark plasma sintering (SPS). Pure HAP does not have good mechanical properties so it is necessary to combine them with other materials, which endow them acceptable strength. Sintering was carried out at various temperatures (700 °C and 900 °C) and holding times (5 and 10 min). Rapid processing time and low sintering temperatures was of importance to avoid HAP decomposition. Mechanical and structural properties of the sintered bodies were studied with different methods. The highest relative density ~96% was obtained at 700 °C sintering temperature regardless of the holding time. Composite with the best mechanical properties (hardness ~4 GPa, 3-point bending strength ~119 MPa) consisted of HAP elongated grains with average length of 300 nm. The GNPs were agglomerated and located on grain boundaries closed to porosities. The structural observation confirmed increased fraction of hexagonal shaped grains, and poorer mechanical properties with increased sintering time and temperature.