Study On Preparation Of Nanometer Bioceramic Materials And Electrophoretic Deposition Of Hydroxyapatite

Hydroxyapatite (HAP), formulated as Caio(PO4)e(OH)2, has become a favorable biomaterial for implants since its chemical composition and crystal structure are similar to the calcium phosphate minerals present in biological hard tissue. The clinical use of HAP as a load-bearing implant, however, is limited because of its mechanical brittleness and low tensile strength. Many efforts have been made in recent years in the development of processing methods for depositing HAP on the implant alloy substrate in order to have high strength as well as excellent biocompatibility and bioactivity. Electrophoretic deposition of HAP bioceramic coatings has recently attracted considerable attention because of a variety of advantages of the method of the coating fabrication, such as a low process temperature, ability to deposit on porous or complex shapes of substrate, the simple control of deposit thickness.It has been studied in this thesis that nanometer hydroxyapatite materials were fabricated by a wet method and bioceramic coatings of hydroxyapatite were prepared by the electrophoretic deposition (EPD) technique. The major results and conclusions are summarized as follows:1. Hydroxyapatite for EPD was prepared by wet method using CaCO3 and H3PO4 as the raw materials. The crystal structure and chemical composition of the product were determined by X-ray diffraction (XRD) and Fourier transform infrared(FTIR). The results show that the high pure nanometer hydroxyapatite materials can be prepared while CaO obtained from the decomposition of CaCO3 reacted with H3PO4 for 96 hours in the Ca/P ratio of 1.67.2. HAP coatings on clinical alloys were obtained by electrophoretic deposition that is a combination of two processes: electrophoresis and deposition. Electrophoresis is the motion of charged HAP particles in a suspension under the influence of an electric field, and deposition is the coagulation of HAP particles to a dense mass. The sintered surface of bioceramic coatings deposited by electrophoresis method was detected by scanning electron microscopy (SEM) and X-ray diffraction (XRD). Accordingto the relationship of the deposition time versus the deposit weight and the current density as well as deposit weight versus applied voltage, a model of capacity charging is proposed to explain the process of EPD.3. The kinetics of EPD was studied under the precondition that the charged powder of HAP is the only carrier of electric charge in suspension. The kinetic equations are developed for constant-current and constant-voltage EPD using mass balance conditions. The formula of deposition weight versus time as well as the relationship of velocity versus deposition time could be derived from the experimental data of current versus time, which is obtained under the condition of constant voltage and constant concentration of HAP, and the relationship between observed current and velocity of HAP powders, which results from the theoretical kinetic equation and experimental data measured at the condition of constant current and constant concentration of HAP. The calculated kinetic curve is better fit at the beginning of EPD to the experimental curve plotted under the condition of constant voltage and constant concentration of HAP.