Youn-Ki Jun

Synthesis and dissolution behavior of β-TCP and HA/β-TCP composite powders

Abstract Calcium phosphate powders, β-TCP and biphasic HA/β-TCP, were synthesized by calcining the powders obtained from the co-precipitation method using Ca(NO3)2·4H2O and (NH4)2HPO4. The effects of the initial Ca/P ratio and pH of the solution on the phase evolution and in vitro dissolution behavior of the powders in a Ringers solution were investigated. The Ca/P ratio of the resulting powders was strongly dependent on the pH of the solution and weakly dependent on the initial Ca/P ratio. Single phase TCP powder was obtained at pH=7.4 and the initial Ca/P ratio had a little effect on the resulting Ca/P ratio. Biphasic composite powders were prepared at pH=8.0 and the Ca/P ratio of resulting powder was controllable by adjusting the initial Ca/P ratio. TCP powder showed the highest dissolution rate in the Ringers solution and biphasic composite powder exhibited an intermediate dissolution behavior between that of HA and TCP.

The fabrication and biochemical evaluation of alumina reinforced calcium phosphate porous implants.

Alumina reinforced calcium phosphate porous implants were manufactured to improve the mechanical strength while maintaining the bioactivity of calcium phosphate ceramics. The alumina porous bodies, which provided the mechanical strength, were fabricated by a polyurethane sponge method and multiple coating techniques resulted in the porous bodies with a 90-75% porosity and a compressive strength of up to approximately 6MPa. The coating of hydroxyapatite (HAp) or tricalcium phosphate (beta-TCP) was performed by dipping the alumina porous bodies into calcium phosphate ceramic slurries and sintering the specimens. The fairly strong bonding between the HAp or TCP coating layer and the alumina substrate was obtained by repeating the coating and sintering processes. The biochemical evaluations of the porous implants were conducted by in vitro and in vivo tests. For in vitro test, the implants were immersed in Ringers solution and the release of Ca and P ions were detected and compared with those of calcium phosphate powders. For in vivo test, the porous bodies were implanted into mixed breed dogs and bone mineral density measurements and histological studies were conducted. The alumina reinforced HAp porous implants had a higher strength than the HAp porous implants and exhibited a similar bioactivity and osteoconduction property to the HAp porous implants.

Dielectric and magnetic properties in Ta-substituted BiFeO 3 ceramics

The dielectric and magnetic properties were investigated in Ta-substituted BiFeO 3 polycrystalline ceramics synthesized by a solid-state reaction. The Ta substitution decreased the grain size by two orders of magnitude compared with that of unsubstituted ceramics and increased the electrical resistivity by 6 orders of magnitude. The high resistivity and low dielectric loss allowed the dielectric constant to be determined at room temperature. The magnetic hysteresis loops were observed in the Ta-substituted BiFeO 3 , and the appearance of ferromagnetism was closely associated with the distortion of the oxygen octahedra by the Ta substitution. The coupling between the electric and magnetic dipoles was examined by determining the changes of the dielectric constant with the external magnetic field.

Niobium과 Cobalt를 첨가한 Multiferroic BiFeO₃ 박막의 유전 및 자성 특성

The effects of Nb and Co ion substitution on the dielectric and magnetic properties of the multiferroic BiFeO₃ thin films have been investigated. Heteroepitaxial BiFeO3 thin films were deposited by Pulsed Laser Deposition method. Nb substitution decreased the leakage current by 6 orders of magnitude and Co substituted BiFeO₃ thin films showed an enhanced magnetization, 2 times larger than that of un-substituted BiFeO₃. Through the co-substitution of Co and Nb, BiFeO₃ thin films with a low leakage current and an enhanced magnetization could be obtained.