In-Flight Temperature and Velocity of Powder Particles of Plasma Sprayed Hydroxyapatite

This paper presents a systematic research on the process of thermal spraying of HA encompassing all stages of layer deposition: powder production & characterization (optimized production led to spherical ~40 mm powder with no TCP or TTCP phases), plasma jet properties influence on the in-flight powder properties (major influence of spray distance factor), the influence of the in-flight temperature and velocity of hydroxyapatite powder particles (ranges of 2350 K to 2724 K and 160 m.s-1 to 287 m.s-1) on the final characteristics of the deposited coatings. Six combinations of the system parameters leading the low-medium-high in-flight properties were selected and the respective coatings were investigated, with some data in contradiction to previously published results. It was found that the temperature of the particles significantly influences the microstructure of the coatings, its respective surface roughness levels (Ra = 7:4 to 13:9 mm) and plays a critical role for the development of detrimental CaO (content increase of up to 14.6%) and metastable TTCP (up to 49.5%) phases in the coatings.