Study On The Preparation Of Hydroxyapatite Whisker By Hydrothermal Mothed And The Mechanism Of Needle-like Growth

Hydroxyapatite(HA) whisker, with its good biological characteristics and mechanical properties, is a promising biomaterials. Hydrothermal is a excellent method to synthesize hydroxyapatite whisker; whisker gained by this method has the uniform morphology and stable properties.In this paper, the preparation of hydroxyapatite whisker by hydrothermal method is described. Well-crystal CaHPO4 are selected as initial materials. The properties of the synthetic HAP whisker are tested and analyzed systematacially. the effects of the temperature of the system, the heating speed, the pressure and the granularity of initial materials on growth of HA whisker are discussed. The paper also analyzed the crystal defeat formed in the process of growth and put forward to the solution, furthermore, the mechanism of needle -like growth was discussed.The experiment results indicate that needle-like single crystal with 1mm in length, 60-80 in length/diameter ratio can be gained by hydrothermal method. In experiment, it was found that the solubility of CaHPO4 could be affected by the temperature of the system, the heating speed, the pressure and the granularity of initial materials easily. So that the growth of hydroxyapatite whisker was affected because of the change of supersaturation. In addition, low pH and low supersaturation were in favor of the needle-like growth of hydroxyapatite whisker. The mechanism of needle -growth was presented as follow: The growth unit in c-axis was anionic coordination Ca-P6O24 and the growth unit in a, b-axis were OH-Ca6, As result, the anionic coordination Ca-P6O24 was easy to be adsorbed to the crystal face because of the positive charge on the crystal face in acidic system, but a, b-axis were opposite. At the same time, in acidic system, the lowest concentration of OH" also limited the growth of a, b-axis. In addition, the growth mechanism of c-axis was Screw dislocation growth or rough interface growth, but that of a,b-axis was two-dimension nucleation growth. Because in low supersaturation, the speed of helix dislocation growth and rough interface growth was higher than that of two-dimension nucleation growth. It leaded to the needle-like growth of hydroxyapatite whisker.