Calcium Phosphate Coating on Titanium Plates by Electrodeposition
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Calcium Phosphate Coating on Titanium Plates by Electrodeposition Masahiko Ishikawa, Kouji Nishikawa, Kensuke Kuroda, Ichino Ryoichi, Masazumi Okido and Osamu Takai Nagoya University, CIRSE, Furo-cho, Chikusa-ku, Nagoya, 464-8603, JAPAN ABSTRACT Calcium phosphate films were deposited on titanium electrodes cathodically from CaCl2 ･ 2H2O and Ca(H2PO4)2 ･ H2O aqueous solutions. In this study, H2O2 addition into electrolytes was applied to enhance the electrochemical process at the solution/electrode at a smaller cathodic potential than no H2O2 addition. Deposited films were analyzed by scanning electron microscopy (SEM) observation and X-ray diffraction (XRD). Cathodic current of the Ti electrode decreased once and increased in the solution with H2O2. It shows a cathodic current peak at c.a. 25 min in the case of potentiostatic condition at - 0.756 V (vs. Ag - AgCl, sat. KCl). The calcium phosphate film grows mainly with the decrease in current after the cathodic peak. The characteristics for the electrodeposited film such as crystal morphology depends on cathodic potential, solution pH, deposition temperature and amount of H2O2 addition. Dense calcium phosphate film composed of relatively good crystalline was obtained at pH 5.5 and – 0.756 V. Film adhesion on Ti appeared to be strong by peeling test. At larger cathodic potential of – 1.156 V, the film coverage on titanium plates was smaller and film adhesion worsened. Larger cathodic polarization of more than – 1.556 V was necessary to reduce water in case without H2O2 addition. INTRODUCTION Hydroxyapatite (Ca10(PO4)3(OH)2, HAp) is widely known as a promising material with an excellent bioactivity, therefore many researchers have been concentrated in development of HAp or other calcium phosphate coating techniques on titanium alloy for medical implantation in recent years [1,2]. Plasma spraying method has been of practical use as a high-speed deposition process [3,4], though this method is operated at higher temperature which increases operating cost and may cause phase transition of deposits. In order to overcome disadvantages of the conventional process, the present authors have alternatively paid attention to “soft solution” processes such as the electrophoretic method, biomimetic method, etc [5,6]. Among these soft solution processes, electrolytic deposition process has been a newly developed method, which enables us to form HAp coating film at larger deposition rate and that can be operated at nearly room temperature, atmospheric pressure and low equipment cost [7]. HAp deposition can be conducted in aqueous solutions containing both calcium and phosphate ions utilizing electrolytic production of hydroxyl ion. In this manner, supersaturation of HAp is increased especially in the vicinity of electrode enhancing heterogeneous nucleation. The problems in conventional studies are that hydrogen gas generated by reduction of water might deteriorate film adhesion and that reduction of water requires relatively larger cathodic polarization. In our new proposal for impro
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