Étude de la préparation de poudres et de dépôts à partir de suspension par plasma inductif le cas de l'hydroxyapatite phosphocalcique

Abstract

The work presented in this thesis has been directed to the study and the development of a new thermal spray process now known as the"SPS" (Suspension Plasma Spraying), in which the raw material to be treated is initially a liquid suspension.The SPS process is employed either for the preparation of thick coating or to the production of spherical and dense powders. The principle of SPS is the axial injection of a suspension into the plasma core by gas atomization.The atomization droplets are successively dried, melted and accelerated in the plasma plume. Finally, melt droplets strike a substrate and solidify to build the coating (deposition route) or are solidified in-flight and are then collected from within the reactor (powder route).The SPS process is best achieved with the use of r.f. thermal plasma technology and has been applied to the complex shape forming of ceramic materials: e.g. hydroxyapatite (HA), Ca[subscript]10 (PO4 )[subscript]6 (OH)[subscript]2 . HA, which is a bioceramic used in various biomedical applications such as bone substitute. The original chemical synthesis of the HA is a key step for the control of physical and chemical properties of the HA suspension which in turn are fundamental to the success of the entire SPS process. HA decomposes at elevated temperatures. With proper control of the plasma spraying parameters (i.e. the nature of the plasma gas and its composition, plasma power level, pressure, etc), the in-flight plasma decomposition can be minimized. Moreover it is possible to control the coating texture, its crystallinity and adhesion strength while maintaining high deposition rates (>150 [micrometre]/min).The morphology of powders prepared by the SPS technique and the size of resultant powders depends strongly on the atomization parameters of the spray suspension in the plasma. Water promotes the stabilization of HA during the plasma treatment and therefore helps to limit its in-flight decomposition. The SPS process is a potentially powerful technology providing in-flight reaction routes for new materials synthesis and shaping, both as powders and as finished coatings. A further advantage of the SPS process concerns its economics through the used of a reduced number of process steps required in comparison to conventional plasma spray process