Purity Modification within Sol-gel Derived Hydroxyapatite (HAp) Nanopowders

In this study, the nanopowders of hydroxyapatite (HAp) with three different materials using Ca(NO3)2.4H2O, H3PO4, P2O5, and PO(OC2H5)3 precursors have been synthesized by sol-gel and characterized by some physic-chemical approaches such as XRD, FTIR, DTA, and SEM elemental analysis and their purity have also been investigated. Followings, by the XRD data and with the aim of Scherrer equation, their particle size values have been determined. These results have good agreement with observed particle size within TEM images. It is interesting to note that based on DTA curves, the synthesized sample from PO(OC2H5)3 precursor has been crystallized at 400 ºC that is absolutely lower than the reported crystallization temperature (CT) of other samples. However, the important factors such as sol temperature, aging time and calcination temperature affect product purity. Indeed, the higher sol temperature and aging time increase the product purity. With the increase of the calcination temperature till upper than 600 ºC, calcium phosphate impurity phases transform to HAp. As expected, the mean crystalline size increased with raising in calcination temperature. By increasing temperature from 600 to 700 ºC mean particle size growed from 50 to 98 nm, hence the latter temperature assigned as suitable CT for preparing of the titled nanopowders.