The Crystallization Treatment Of Hydroxyapatite Coating Surface Nano-organization And Its Biological Behavior

This paper mainly deals with plasma sprayed hydroxyapatite(HA) coatings on pure titanium, especially in terms of the microstructure, phases composition and biological performances of nanosized structure on the surfaces of crystallized HA coatings were researched by using X-ray diffraction (XRD), electron probe microanalyser (EPMA), scanning electron microscope (SEM), field emission scanning electron microscope (FE-SEM), atomic absorption spectrophotometer and electric tension machine.The results show that under certain conditions of internal feedstock and the stand-off distance of 80-110mm, fine starting HA powder and higher spraying power lead to the higher melting degree of HA powder and the lower coating crystallinity.The investigation on the as-sprayed HA coatings made from fine powder(FC), coarse powder(CC) and bilayer coatings(BC), indicates that hydroxyapatite decomposes into amorphous HA, tetracalcium phosphate(TTCP), a-trecalcium phosphate(α-TCP) and calcium oxide(CaO). After heat treatment at 650℃ for 0.5h, the amorphous and decomposed phases can almost be transformed into crystalline HA. SEM observation shows that ultra-fine particles with the size of <300nm are formed on the surfaces of the three kinds of HA coatings. The heat treatment increased the shear strength of coating/substrate interface of CC and BC coatings, whereas that of the FC coating decreases by contraries.Nano-particles are prone to form on the BC coatings both as-sprayed and heat treated. After being recrystallized, nano-particles 50～100nm in size form more easily on the coatings sprayed in internal feedstock model. XRD analysis and chemical composition examination show that these nano-particles are mainly of apatite. At the same time, the heat treatment caused the nano-particles with the size of about 20nm reunite into spherical or irregular aggregates. More, the repetitious heat treatment made them form hard aggregates with the size of 100～200nm. The formation of nano-particles on the surfaces of splats were limited within the coatings and then little nano-particles were formed.The biological safety appraisal test indicates that bilayer coatings heat treated at 650℃ for 0.5h(BBC) do not cause stimulate effects and anaphylaxis inferior...