Electrochemical Preparation Of Silicon-substituted Hydroxyapatite And Amorphous Calcium Phosphate Along With Their Composite Coatings

Silicon-substituted hydroxypaptite(Si-HA) and amorphous calcium phosphate (Si-ACP) coatings along with their composite coatings were prepared by electrochemical depostion on titanium substrate. The effect of silicon content on coatings microstructure and propertites and the formation mechanism were studied. The deposition process was all conducted at a constant voltage of 3.0V for 1h. The chemical compositions, microstructure and micro-morphologies of coatings were characterized with scaning electron microscope(SEM), X-ray diffraction(XRD), Fourier transform infrared spectroscopy(FTIR), and inductively coupled plasma(ICP).1) Silicon-substituted hydroxyapaptite coatings were obtained with electrochemical deposition technique in electrolytes containing Ca2+, PO43- and SiO32- ions at 85℃.The results show that the silicon amount in Si-HA coatings deposited by electrochemical method can reach to a saturation level of around 0.55wt%, and the substitution of silicate for phosphate in the form of SiO44- results in loss of some OH-to maintain the charge balance. Additionally, the presence of silicon ions in electrolytes inhibits HA crystals growth in coatings, leading to decrease of coating thickness and transformation of rod-like crystals into dendritic crystals in the electrolyte of 20% molar ratio silicon.2) Silicon-contained amorphous coatings were prepared with addition of Na3cit and Na2SiO3 in Ca-P electrolytes at 60℃. The results suggest that the Na3cit can promote the formation of ACP while the Na2SiO3 can make the ACP particle uniform, and the Si/P ratio is increased and the ACP particle size is reduced in coatings when the silicon content in electrolytes is increased, however the Ca/P ratio is kept at level of about 1.8 and the silicon does not fully enter the coating by the assuming ratio in electrolyte.3)Using the transformation of ACP to HA whose mechanism is surface mediated crystallization, the HA/ACP composite coatings can be acquired by one step at 85℃, and the more silicon content in electrolyte, the less HA content in composite coatings. Moreover the composite coatings in which the interspace of HA crystal is filled by ACP can be gained by firstly deposition of Si-HA coating then by Si-ACP coating, however the more silicon content of electrolyte, the less ACP content in coatings.