PHYSICAL AND MECHANICAL PROPERTIES OF HYDROXYAPATITE CERAMICS WITH A MIXTURE OF MICRON AND NANO-SIZED POWDERS: OPTIMISING THE SINTERING TEMPERATURES

In order to determine the optimum sintering temperatures of hydroxyapatite ceramic sintered bodies, while maintaining high physical and mechanical properties, pellet-shaped hydroxyapatite (HA) samples were prepared by controlling micron-and nano-sized powders. Determining the optimum sintering temperature aims to avoid changes in the HA phase and reduce excessive grain growth at too high temperatures. The samples were made by mixing micron-and nano-sized HA powders at a ratio of 80:20 wt. % and adding polyvinyl alcohol (PVA) of 10 wt. % as a binder. Green bodies were made using the uniaxial pressing method under a pressure of 200 MPa. The initial heating was carried out at a temperature of 700 degrees C for 1 h to remove the PVA, followed by a sintering process performed at temperatures ranging from 1000 degrees C to 1200 degrees C with a holding time of 2 h. The results showed that the optimum sintering temperatures ranged from 1150 degrees C to 1200 degrees C, with no significant linear shrinkage occurring at those temperatures. In the microstructural analysis, a significant decrease occurred in the number of pores in the sintered bodies at a temperature of 1200 degrees C. The mechanical properties are maintained at a high level at sintering temperatures of 1150 degrees C and 1200 degrees C, i.e., Vickers hardness values of 4.40 GPa and 5.67 GPa, respectively.