Compaction and sintering of Hydroxyapatite

Abstract

The effect of compaction load, sintering temperature and soaking time on the sinterability and densification of Nanocrystalline hydroxyapatite (HA) was assessed in this work. The compaction and sinterability of Nanocrystalline hydroxyapatite (HA) particles was done at three different compaction loads and temperatures ranging from 1 ton to 5 ton and 850⁰C to 1250⁰C respectively. Green and sintered densities of the compacts were analyzed by Archimedes method (for density measurements) for the influence of these parameters. The results revealed that compaction of the green pellets was best achieved at 5 ton compaction load and its percent green densification was up to 50% of the theoretical density of HA (3.16g/cm3 ). For sintered density, the best results were achieved at a temperature of 1250⁰C and a compaction load of 1 ton which were 98% of the theoretical density. Soaking time at these sintering temperatures was varied between 1 and 3 hours and was found that with the variation of soaking time from 3 hours to 1 hour, the sintered density decreased tremendously at 850⁰C from 85% to 50% whereas at higher temperatures the decrease in density was only 4 to 6%. Vickers micro hardness testing and biaxial flexural testing was used to evaluate hardness and flexural strength of sintered compacts respectively. The maximum hardness of 625 (+28) HV1 and flexural strength of 40 (+10) MPa was obtained for HA sintered at 1250⁰C with a soaking time of 3 hours. Phase analyses were carried out using an X-Ray diffractometer. The HA phase was stable even at the highest sintering temperature of 1250⁰C and did not decompose into α tri-calcium phosphate (TCP) and β TCP.