Plasma coating of hydroxyapatite

Characteristics of the hydroxyapatite (HA) plasma coatings are directly related to the performances of the plasma jet used in the deposition process. Previous research within a plasma spray technique, based on the application of the conventional plasma gun (PG), suggested the use of lower power level of the PG, about 25kW, in order to avoid significant chemical decomposition of HA occurring at higher powers. However, coatings obtained at this power level have a poor microstructure, resulting in their unsatisfactory cohesion/adhesion properties. In contrast to that, this study shows that good quality HA coatings can be produced in plasma obtained by plasma jet operated at high power level (52 kW) and in laminar flow mode. For two HA powders types, containing particles differing in mass by a factor of 20, a set of optimum deposition parameters has been defined leading to the coatings with high crystallinity (80-90%), excellent microstructure (porosity 1-2%) and high adhesion strength (60 and 40 MPa for the coating thicknesses of 120 and 350 mu m, respectively). It has been shown that higher plasma power does not necessarily lead to a higher HA decomposition.