Microstructure Of Hydroxyapatite Research Articles

Improvement of the microstructure and microhardness of hydroxyapatite ceramics by addition of lithium

Abstract The aim of this work is to improve sintered density, microhardness and microstructure of hydroxyapatite (HA) ceramics, sintered in air at 1200 °C with the addition of lithium ions. Samples were characterized by density measurements, X-ray diffraction (XRD), Vickers microhardness, and scanning electron microscopy (SEM). Also, conductivity vs. time curves and dissipation factor measurements between 100 Hz-1 MHz were made in order to relate composition and microstructure characteristics with electrical behavior.

Physics of hydroxyapatite plasma coatings on TiNi shape memory materials

The microstructure of hydroxyapatite (HAP) ceramics coatings on TiNi shape memory alloy substrates was investigated. From the point of view of adherence, these coatings posses higher strength than approx. 30 MPa. The three levels of power input parameters were applied during the spraying process (55, 50 and 45 V). At lower voltage, the prepared HAP coatings contained pure Ca 10(PO 4) 6(OH) 2 with a Ca/P ratio of 1.65. At the highest voltage (55 V), the transition phase Ca 10(PO 4) 6(OH) 0.5O 0.75 was detected. The observed good metal/ceramic interface strength is given by the formation of chemical bonding and by the energy dissipation due to stress induced martensite formation (SIM) and/or martensite reorientation (RE) during stressing the investigated composite.

Sub-Micrometer Hydroxyapatite Bioceramics

AbstractWe studied the microstructures of hydroxyapatite (HA) ceramics which were sintered under three different conditions. It was found that all the ceramics were of sub-micrometer structure. The synthetic HA ceramics were also compared with human enamel. It is concluded that human enamel has higher strength because of its unique microstructure.

Kinetics of Hydroxyapatite Formation at Low Temperature

The influence of temperature on the kinetics of formation of calcium‐deficient hydroxyapatite by an acid‐base reaction has been determined. Calcium‐deficient hydroxyapatite is compositionally similar to bone apatite. Reactants used in this study were tetracalcium phosphate, a calcium phosphate more basic than hydroxyapatite, and dicalcium phosphate, which is more acidic than hydroxyapatite. The kinetics of hydroxyapatite formation are initially controlled by the surface areas of the reactants; however, eventually the rate of hydroxyapatite formation becomes diffusionally controlled. The origin of diffusion control appears to be associated with the epitaxial formation of hydroxyapatite on the surface of the dicalcium phosphate reactant. The microstructure of hydroxyapatite formed at 5°, 15°, and 25°C were generally similar and are characterized by the formation of a porous acicular product which covers the surfaces of the reactants. The microstructure of the hydroxyapatite formed at 38°C was distinct from this and exhibited a pseudomorphic relationship with the dicalcium phosphate reactant. Seeding with hydroxyapatite accelerated the initial reaction but did not appear to have major long‐term effects on the fractional degree of reaction or on microstructural development. Reaction was also accelerated in a neutral salt solution of high ionic strength.