Long-Hao Li

Hydroxyapatite-TiO2 Hybrid Coating on Ti Implants

A hydroxyapatite (HA)-titania (TiO2) hybrid coating is developed to improve the biocompatibility of titanium (Ti) implants. The HA predeposited layer on Ti via electron beam (e-beam) evaporation is subsequently treated by micro-arc oxidation (MAO) to produce an HA-TiO2 hybrid layer on Ti. The e-beam-deposited HA layer has a thickness of ≈1 μm and was highly dense prior to MAO. By means of MAO treatment, a rough and porous TiO2 layer is formed beneath the HA layer with a simultaneous local dissolution of the HA layer. Due to the HA precoating, high concentrations of Ca and P are preserved on the coating surface. The osteoblast-like cells on the hybrid coating layer grow and spread favorably. The cell proliferation rate on the hybrid coatings is not much different from that on pure Ti or simple MAO-treated Ti. However, the alkaline phosphatase (ALP) activity of the cells is significantly higher (p < 0.05) on the HA-TiO2 hybrid coatings than on either the pure Ti or the simple MAO-treated specimen, suggesting that the cellular activity on the hybrid coatings is improved.

Electrostrictive properties and polarization mechanisms of Pb(Zn1/3Nb2/3)O3 based ceramics

Abstract Both the electrostrictive strain and electric polarization of Pb(Zn1/3Nb2/3)O3-BaTiO3-PbTiO3 ceramics near MPB were carefully measured as a function of electric field strength, and temperature. The longitudinal strain versus the polarization squared with varying compositions was also analyzed. In terms of their domain structure and x-ray diffraction pattern under different dc bias, the field-induced domain switching and polarization mechanism of ferroelectric ceramics is discussed. It should be stressed that microdomains and macrodomains each provide a different contribution to the field-induced strain.

Hydroxyapatite 분위기 소결을 통한 지르코니아 표면 경도 강화

To increase the mechanical property of zirconia, we have investigated the phase change and the resulting hardness of zirconia ceramics by hydroxyapatite (HA) powder bed sintering. It was observed using X-ray diffraction that the cubic zirconia phase, which has a higher hardness value than that of the tetragonal phase, was obtained at the surface of 3 mol% Y2O3 doped tetragonal zirconia polycrystal (3Y-TZP) ceramics during the sintering process; in our experimental conditions, the phase change at the surface increased as the sintering time increased. We believe that the observed crystalline phase change originated from the decomposition of HA and the diffusion of CaO, as follows. CaO, which was derived from the decomposition of HA at high temperature (1400˚C), diffused into the surface of 3Y-TZP and acted as a stabilizer. As a result, the Vickers hardness value of the treated specimens was higher than that of the non-treated specimen due to the formation of the cubic phase on the surface of 3Y-TZP.

Electric field dependence of the dielectric properties of Pb(Zn1/3Nb2/3)O3-BaTiO3-PbTiO3 ceramics

Abstract The dielectric behavior of Pb(Zn1/3Nb2/3)O3-BaTiO3-PbTiO3 under various dc bias conditions was measured and analyzed over a broad temperature range. The dc bias field reduced the dielectric constant, increased the temperature of the dielectric constant maximum, and suppressed frequency dispersion. The coherence of the characteristic temperatures was clearly observed between the dielectric constant and the dielectric loss, which is considered to be associated viscous movement of domain walls. It is suggested that the dc bias field significantly influences the freezing process of polar microregions and changes the density of domain walls.