J. L. Xu, School of Mechanical & Aerospace Engineering, Nanyang Technological University, Singapore, Singapore; K. A. Khor, Nanyang Technological University, Singapore, Singapore; R. Kumar, Department of Environmental Engineering, Montana Tech of the University of Montana, Butte, MT
Inductively coupled radio frequency (rf) plasma spraying, powered by high-frequency oscillating electrical current, performed an important role in fine powder manufacture. It was used in the present study to prepare fine spherical bioceramic powders of hydroxyapatite (HA) whose chemical composition similar to those of natural bone. The as-sprayed powders consisted of both micron-sized spherical particles and nano-sized particles. In addition to the spheroidization effect, rf plasma treatment led to the decomposition of HA into secondary calcium phosphate phases including tri-calcium phosphate, tetra-calcium phosphate and calcium oxide. The microstructure investigation showed that the spheroidized particles were either fully dense or hollow structure with a shell. The results indicated that columnar grains grew from the surface to the core of the dense particles by the driving force of heat flow. The reason for the formation of hollow spheres was contributed to the higher density of the solidifying surface layer compared with the melted phase during solidification.
Summary: Fine nanostructured bioceramic powders were spheroidized using a inductively coupled radio frequency plasma spraying technique. The powder morphology, phase compositions and inner structure were investigated by advanced method such as Focused Ion Beam (FIB) system which helped to obtain the cross-sectional images of the structure.
