Excellent biocompatibility of hydroxyapatite (HA) is the main reason of application plasma-sprayed coatings onto orthopedic prostheses. A careful optimization of spray parameters is necessary to avoid thermal decomposition of HA onto less biocompatible products such as e.g. tricalcium phosphate, tetracalcium phosphate, calcium oxide and amorphous calcium phosphates. The spray parameters influence considerably the decomposition and the present study is devoted to understand this influence using on an experimental way. The design of experiments (DOE) was made using two-level 2N plan of experiments (N=5). In total, 32 experiments of spraying were carried out by varying following operational parameters: (i) composition of plasma working gases; (ii) electric power input; (iii) art of spraying (into water or onto substrate); (iv) carrier gas flow rate and; (v) art of injection (external and internal). Plasma-sprayed coatings and powders were analyzed by Fourier Transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD). The X-ray diagrams enabled to find the content of crystal phases. The content was a first response function described by a polynomial regression equation. The morphology of obtained deposits was also characterized using Scanning Electron Microscope (SEM). Their porosity was estimated using image analysis of coatings cross section images.

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