Experimental study of suspension plasma spraying of hydroxyapatite

Thermal plasma spraying is a suitable technique for hydroxyapatite [HA, Ca₁₀(PO₄)₆(OH)₂] coating preparation. Suspension Plasma Spraying (SPS) is a newly developed process based on a suspension of fine (<10 µm) or even ultrafine (<100 nm) powders, axially fed into the r.f. plasma through an atomization probe. The atomization of the suspension results in microdroplets (20 µm in size). They are flash dried, melted and finally impacted onto the substrate to solidify and build the coating. The aqueous suspension of HA is chemically synthesized. Our experiments included variations of the plasma gas composition (Ar/0₂, Ar/H₂), the plasma deposition reactor pressure. Characterizations techniques (e.g. X-ray diffraction, scanning electron microscope and transmission electron microscope) were applied to resultant SPS HA coatings which possessed good crystallinity and about 3% weight α-TCP and lime. The texture examination has shown that preferential crystal orientation followed the (001) Miller's plane family. SPS by r.f. induction plasma has proved to be a reliable process for the production of thick (200 µm) HA coatings with high deposition rate (>150 µm/min).