Relationship between plasma spray operational parameters and microstructure of hydroxyapatite coatings and powder particles sprayed into water

A full factorial design of 24 experiments was used to determine the effects of four principal plasma spray parameters (i.e., plasma forming gas composition, electric power, spraying distance, and carrier gas flow rate on the microstructure of hydroxyapatite (HA) coatings and powders). The granulometry of powders was tested after spraying into water and compared to the initial one. The crystal phase content of powders and coatings was determined using quantitative X-ray diffraction (XRD) analysis. The morphologies of coatings surfaces, cross-sections, and particles sprayed into water were characterized using scanning electron microscopy (SEM). The mapping of elements inside plasma-treated powders was carried out using electron microprobe analysis (EMPA). Infrared spectroscopy (FTIR) allowed determination of the dehydration of HA under different spray conditions.