Suspension plasma spraying for hydroxyapatite powder preparation by RF plasma

Numerous techniques have been developed to synthesize ceramic powders with improved physical and chemical characteristics. This paper describes a new process called suspension plasma spraying (SPS), based on the use of radio frequency (RF) plasma technology. The objective of SPS is to prepare dense and spherical powders from a suspension of fine (<10 pm) or even ultrafine (<100 nm) powders. The precursor for SPS is a colloidal suspension (or physical gel) which is gas atomized in the plasma. Liquid evaporation, consolidation, and sintering occur during the plasma heat treatment. Results concerning the preparation of a bioceramic (hydroxyapatite, HA) powder from an aqueous suspenslon precursor are reported. Process variables are studied as a function of phase structure morphology and crystallinity of the obtained powder. The plasma power was kept in the range 35-45 kW; the plasma gas was a mixture of Ar/H₂ or Ar/O₂. Investigations by X-ray diffraction (XRD), scanning electron microscopy, transmission electron microscopy, and infrared spectroscopy were performed on the suspension as well as on the produced powders. Atomized HA particulates are pure, dense, and well spheroidized, with an average particle diameter of 20 μm