Methods: According to the sol-gel technique, thiethyl phosphite (P(OC2H5)3) was hydrolyzed with distilled water (DW). Calcium nitrate (Ca(NO3)2 was dissolved in DW and this solution was added to the hydrolyzed phosphate sol. The mixed solution was kept static at 45oC for 2 h (aging time). The aged sol was then subjected to thermal treatment (drying time). The dried gel was calcined by applying a constant heat rate of 10oC/min up to 500oC, and then further calcined for 10 min. The final product was ball-milled to get a fine powder texture. A sample of the synthesized HA was mixed with a deflocculating agent at a 3:1 ratio in an attempt to further reduce the size of the particles. The nano-HA was characterised using x-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM).
Results: The XRD results showed that there was a good match between the experimental and theoretical HA spectra. The manufactured HA was also compared with commercially available HA. Factors such as the aging and drying time, and the temperature play an important role in the crystallinity and morphology of nano-HA. SEM results indicated that nano-HA formed agglomerates, which were further characterised with TEM. These particles were found to have dimensions between 50nm and 70nm. In the samples that deflocculant had been used, individual HA particles appeared to be as small as 10nm. The deflocculant appears to affect the morphology and distribution of the HA particles.
Conclusions: Nanoparticulate HA was synthesized using the sol-gel technique. Sub 100nm particles were obtained and their size was further reduced by mixing with deflocculating agents.