Interdependence of different properties of hydroxyapatite coatings and powders plasma sprayed into water

Plasma spraying process was applied to deposit Ca10(PO4)6(OH)2, hydroxyapatite (HA) coatings onto metallic substrates and to recover powders after their trajectory in plasma into distilled water. The processes had four variables: electric power input, plasma gas composition, carrier gas flow rate, internal or external injector. The variables were used in low and high level enabling 24 experiments to be realized. Phase composition of obtained coatings was tested with X-ray diffraction (XRD). The technique enabled to find out that a part of HA in initial powder decomposed at processing into tricalcium phosphate (α-TCP) and tetracalcium phosphate (TTCP). Coatings microhardness was tested using indentations of the coatings cross-sections. The powders treated in plasma jet and recovered in water were analyzed using laser particles sizer and their morphology was interpreted with a help of an optical microscope. The results of coatings and powders characterizations were statistically treated with the principal components analysis (PCA) using Statbox software in order to find out the correlation between them. The final task of this analysis was to determine which characteristics correlate at strongest with content of crystalline hydroxyapatite in sprayed coating. This content determines their quality in biomedical applications.