Formation of Titanium Dioxide Containing Calcium Phosphate Crystallites: A New Process
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combine the properties of titanium with those of the phosphates. Dental implants and hip prosthesis are fabricated using titanium coated with an HA layer. At present, the most commonly used technique for coating is plasma spraying [3]. However the technique has the double disadvantage of spoiling the crystallinity as well as the stoichiometry of HA [4]. These deteriorations can strongly affect the degree to which the coatings resist dissolution, and therefore its attachment to bone and adherence to the implant [5]. Ideally, one would like to produce an implant surface composed of TiO 2 layers mixed with HA, such that there is a gradual transition from a pure TiO2 structure to a pure HA structure by varying the Ti/Ca ratio. In this paper we propose a method to produce TiO 2 containing HA crystallites. EXPERIMENT Samples preparation Samples were prepared by room temperature precipitation. A flow chart of the method is presented in Fig. 1. 81 Mat. Res. Soc. Symp. Proc. Vol. 414 01996 Materials Research Society
Figure 1: Processing schematic for preparation of TiO 2 containing CaP crystallites Solutions composition i) Calcium and phosphate solution (solution A): a 0.1M solution of extra pure calcium chloride hexahydrate (CaCI2 +6H20; Fluka, Buchs, Switzerland) and a 0. 1M solution of ortho-phosphoric acid (H3PO4 85% purity; Fluka, Buchs, Switzerland) are mixed in the correct proportions to obtain a Ca/P ratio of 1.67 to build HA and a Ca/P ratio of 1.5 for P3-TCP. Distilled water is added until a Ca concentration of 10- 2 M is reached. ii) Titanium solution (solution B): titanium tetrachloride (TiCI4 98% purity; Fluka, Buchs, Switzerland) is diluted in a 6M solution of hydrochloric acid (HCI) until a concentration of 0.5M is obtained. iii) Alkaline Solution (solution C): An appropriate quantity of IM solution of pure potassium hydroxide (KOH)is used to neutralize the H30+ ions present in solutions A and B. Preparationmethod Solution C is added to solution A while constantly stirring. After a precipitate forms, solution B is added slowly. The Ti/Ca ratio is usually fixed at unity. The solution is then filtered. The resulting precipitate is dried and then sintered. Sintering temperatures are chosen between 900'C and 1000°C, and durations of between 18 and 48 hours. Sintering is performed in either an oxidizing (air), or neutral (argon) atmosphere or a vacuum of 2.10-3 Torr. Characterization techniques The crystalline structure was determined using X-ray Diffraction (XRD), surface chemistry by Xray Photoelectron Spectroscopy (XPS), bulk chemistry using Energy Dispersive X-ray Analysis (EDX) and morphology by Scanning Electron Microscopy (SEM). 82
X-ray powder diffraction was done at room temperature with a Siemens D-500 diffractometer with Cu Kat radiation. Each specimen was prepared by sticking the sample powder onto a plexiglass holder using silicon grease. Intensity was measured by step scanning in the 29 range between 200 and 400 with a step size of 0,01' and a measuring time of 10s per point. Phase analysis was p
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