Formation of ultrafine particles in heat treated plasma-sprayed hydroxyapatite coatings

Nanophase materials are expected to enhance the functions of osteoblasts and promote osseointegration. In this study it was found that ultrafine HA particles with nano-grade size can be formed on surfaces of plasma-sprayed hydroxyapatite (HA) coatings after heat treatment. The phases were characterized by X-ray diffraction (XRD). Heat treatment at 600–700 °C for 2 h was found to cause a better crystallization. The restoration of OH− groups was confirmed by Fourier Transform Infrared (FTIR) spectroscopy. Newly formed small HA particles with different shapes, attached to the surface or embedded in the coating, were observed by scanning electron microscopy (SEM). Their microstructure was also examined using transmission electron microscopy (TEM). The calculated average crystal size of these new particles is approximately 100 nm.