Development of hydroxyapatite crystallization utilizing the contact reaction of a minute droplet with atmospheric plasmas

•The fine spherical particles of HAp are generated by plasma crystallization method.•Spherical hollow particles of HAp are also generated.•The presence of citric acid causes the acceleration of HAp crystallization.•Crystallinity of HAp can controllable by the plasma irradiation power. For the creation of a new crystallization method of hydroxyapatite ((Ca10(PO4)6(OH)2); HAp) fine particles through a simplified operation, a combined system of atmospheric plasma with minute droplets was developed. An atmospheric pressure plasma-jet was generated by an inductively coupled plasma method that is contacted to minute droplets including HAp liquid sources as Ca, PO4 and OH elements. In this paper, the effects of the organic compound chemical properties and plasma irradiation power on production of HAp fine particles were examined. Consequently, the fine spherical particles of HAp are generated by the introduction of minute droplets including Ca, PO4 and OH elements into an atmospheric plasma field. Moreover, when citric acid is added to a HAp liquid source for minute droplets, HAp yield is increased 2-times compared to other operations. In conclusion, crystalline HAp is obtained without calcination under conditions of RF irradiation power at 1500W.