Preparation And Properties Investigation Of Hydroxyapatite Particles And Its Coatings

Hydroxyapatite (HAP) is similar in chemical characters and composition to that of the inorganic calcium phosphate of natural bone. It is widely accepted for tissue and bone substitutes with low-bearing due to its excellent biocompatibility and bioactivity. Thus it is of significant value in teeth, reconstructive surgery and clinical medical application. HAP also can be used to treat wastewater with ability in physisorption and chemisorption. In this paper, nano-HAP particles had been synthesized by chemical precipitation and HAP coatings on titanium had also been prepared by electrochemical deposition. Various testing instruments were employed to characterize the phase composition, morphology and some other properties of synthesized particles and coatings. The application of HAP compounding TiO₂ particles as photocatalyst in wastewater treatment was also investigated.Nano-HAP particles had been synthesized by chemical precipitation. The calcining temperature, synthetic temperature, pH value and aging time affected the granularity and morphology of HAP powders. The best synthetic technique preparing HAP had been concluded. When synthetic temperature at 90℃, pH at 10, aging 24h and calcining temperature at 700℃, pure well-crystallized HAP could be obtained. After sintering at normal condition, mechanical properties of HAP could basically meet the requirements of compact bone.HAP coatings on titanium had also been prepared by electrochemical deposition. The effect of voltage, electrolyte temperature and deposition time on the coating was studied and a change tendency can be seen in regularity. The results showed that when voltage at 4V, electrolyte temperature at 30℃, depositing 90min, the coating surface was uniform and the crystal structure was dense, the crystal structures were like blossom cluster with a average thickness at 34μm. Stretching method was adopted to test the adhesion strength between coating and titanium substrate. Adding C2H5OH, H2O₂ into electrolyte or micro-arch oxidizing (MAO) on titanium as a pretreatment can improve the adhesion strength. And the adhesion strength could reach to 7.56MPa/cm² using MAO pretreatment.The bioactivity and electrochemical corrosion resistance of the coatings were evaluated through immersing in simulated body fluid(SBF). The coating surfaces were covered by spherical carbonate apatite layer after being immersed in SBF, a better bioactivity had been proved. And anodic polarization curve verified that the stability of HAP coatings on Ti in SBF was better than pure Ti.Using methylene blue as simulated wastewater, photocatalytic properties of three different TiO₂/ HAP catalysts synthesized by precipitation and pure TiO₂ powders were compared. Different doping ratios of three TiO₂/HAP catalysts were taken into considerate and the optimum doping amount was selected. Adding HAP into TiO₂, then co-precipitating as catalyst was more effective to improve degradation rate of methylene blue. The degradation rate could reach to 80% under proper conditions over HAP/TiO₂=0.5.