Papers by Author: Kug Sun Hong

Abstract: For low temperature cofired ceramic (LTCC) materials to achieve increase functionality, as well as low loss and moderate dielectric constant, it is essential to achieve the temperature stability of the resonant frequency. Facing several empirical approaches toward tuning the temperature coefficient of the resonant frequency (τf) through the formation of mixtures or a solid-solution between the two end members with opposite signs of τf, which result in higher dielectric loss, we took a closer look at the texture engineering that determines the anisotropic dielectric properties in barium niobate ceramics. We demonstrate the advantage of texture engineering for microwave dielectric properties including temperature stability by control of crystallographic orientation. Also, the monoclinic rare earth niobates are investigated as novel microwave dielectric materials. Furthermore, the stable τf of the rare earth niobates could be efficiently explained through the ferroelastic domain engineering related to phase transformation.

Abstract: The effects of CuO and V2O5 addition on sintering behaviors and microwave dielectric properties of 0.7Ca2P2O7-0.3TiO2 ceramics were investigated. With CuO and V2O5 addition, the sintering temperature of 0.7Ca2P2O7-0.3TiO2 can be effectively reduced from 1150 to 950oC. The dielectric constant of the low fired 0.7Ca2P2O7-0.3TiO2 ceramics was not significantly changed while the quality factor was affected by additives. The temperature coefficient of resonant frequency value was increased in negative value with the additive contents. V2O5 and CuO additives effectively improved the densification and dielectric properties of 0.7Ca2P2O7-0.3TiO2 ceramics. The correlation between the phase constituents and the dielectric properties was investigated with additive contents.

Abstract: 5, 10, and 30 nm thickness of transparent TiO2 thin films were fabricated using sol-gel process, and the influence of film thickness on the photocatalytic property was investigated. The increase in film thickness was found to enhance the photocatalytic property of the films. Photocatalytic properties of each film were estimated by decomposition of stearic acid. The amount of decomposed stearic acid increased with film thickness (5 - 30 nm). For the case of 30 nm thickness film, the stearic acid was decomposed perfectly in twelve minutes. UV-vis spectra and photocurrents of each film clearly showed that the photoactivities of TiO2 films were related to the amount of absorbed UV light and band gap shift.

Abstract: The purpose of this study is to compare the osseointegration of calcium pyrophosphate(CPP) coated screws with uncoated screws. CPP coating was prepared and coated by dipping method. CPP coated and uncoated screws were inserted into the mongrel dogs. The insertion torques, radiographs, histology, histomorphometric analysis, and extraction torques were evaluated at 2, 4, and 8 weeks after surgery. The insertion torque was not different between CPP coated and uncoated screws. The extraction torques of CPP coated screws at 2, 4, and 8 weeks(5.45±2.05, 7.62±1.51 and 6.60±2.80 cNM) were significantly higher than their insertion torques(2.74±1.13, 2.98±0.70, and 2.18±1.34 cNM)(p<0.0001, <0.0001 and 0.0005 respectively) and significantly higher than the extraction torques of uncoated screws(1.14±0.470, 2.57±1.36, and 3.18 ±0.499 cNM). The percentages of direct bone-screw contact of CPP coated screws were statistically higher than those of uncoated screws at 2, 4, and 8 weeks. These results suggest that CPP coating may improve the clinical results by allowing early motion exercises and early weight bearing.

Abstract: The purpose of our study is to compare the biodegradation and osteoconduction between CaO-SiO2-B2O3 glass-ceramics(CS10B) and hydroxyapatite(HA), tricalcium phosphate(TCP). Porous CS10B implants were prepared by polymer sponge method. Single-level posterolateral spinal fusions were performed on thirty rabbits. The animals were divided into three groups by implant material: HA, TCP and CS10B. Radiographs checked every two weeks. All animals were sacrificed 12 weeks after surgery. The proportion of the area occupied by ceramics in final radiography on the initial radiography was calculated. Uniaxial tensile strength was measured on 7 cases in each group. The proportion of the area of HA(88.7%±16.1) was significantly higher than those of the others(p<0.05), and the proportion of the area of CS10B(28.2%±9.3) was significantly lower than those of HA and TCP(37%±9.6)(p<0.05). The mean values of tensile strength of the HA(191.4±33.5 N) and CS10B(182.7±19.9 N) were significantly higher(p<0.05) than those of the TCP(141.1±28.2 N). CS10B showed the tensile strength of fusion masses similar to those of the HA, however, more rapid biodegradation than HA and TCP. These findings suggest that CS10B grafts have the possibility as a bone graft substitute.