Densification of nanocrystalline hydroxyapatite powder via sintering: enhancing mechanical properties for biomedical applications

Abstract

The effect of compaction load, sintering temperature and soaking time on the sinter-ability and densification of Nano crystalline hydroxyapatite (HA) was assessed. The compaction and sinter-ability of HA particles was done at three different compaction loads and temperatures ranging from 1 ton to 5 ton and 850 °C to 1250 °C, respectively. Compaction of the green pellets was best achieved at 5-ton compaction load and it’s percent green densification was up to 50% of the theoretical density of HA (3.16g cm−3). For sintered density, the best results were achieved at a temperature of 1250 °C 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 h and was found that with the variation of soaking time from 3 h to 1 h, the sintered density decreased tremendously at 850 °C from 85% to 50% whereas at higher temperatures the decrease in density was only 4 to 6%. The maximum hardness of 625 (±28) HV1 was obtained for HA sintered at 1250 °C with a soaking time of 3 h. Phase analyses were carried out using an x-ray diffractometer. The HA phase was stable even at the highest sintering temperature of 1250 °C and did not decompose into α tri-calcium phosphate (TCP) and β TCP. The grain size was reduced by decreasing soaking time and lowering sintering temperature.