Comparison Of Conventional And Microwave Sintering Of Bioceramics

Hydroxyapatite (HA) presents excellent biocompatibility because of its chemical composition close to that of human bone. However, its low mechanical properties limit the structural uses. An interesting way to improve the mechanical resistance of HA consists in obtaining dense samples with fine microstructure. With this aim, microwaves represent a promising method due to the very short thermal treatment duration. In this study, the direct microwave sintering in a single mode cavity was first investigated: >99% dense samples with submicronic microstructures were obtained in less than 15 minutes of irradiation. The resulting mechanical properties are therefore improved: higher Young modulus (>140 GPa), higher hardness (>9 GPa) than those classically reported with other sintering processes. The obtained results are discussed according to the microstructures and experimental parameters such as sintering temperature and microwave irradiation time. The second part of this work consists in scaling up the microwaves process to obtain larger sized dense parts (more than 40mm diameter). To achieve this goal, sintering was carried out in a 2.45 GHz multimode furnace. The resulting microstructures and mechanical properties are discussed regarding the specific characteristics of this microwaves process.