Ji-Young Yoon

Synthesis of α-SiC from tetramethylsilane by chemical vapor deposition at high temperature

Tetramethylsilane (TMS) is a common liquid-phase precursor that is used in the synthesis of β-SiC by chemical vapor deposition (CVD). At temperatures above 1500 °C, however, it has been shown that C is also formed together with SiC. In this study, based on thermodynamic modeling, we report on the successful synthesis of single-phase SiC with no evidence of the inclusion of C from TMS through CVD at temperatures over 1900 °C. X-ray diffraction data showed that α-SiC phases are formed at temperatures over 2000 °C. On the basis of these results, TMS can be used as a precursor for α-SiC synthesis.

The effect of resin cements and primer on retentive force of zirconia copings bonded to zirconia abutments with insufficient retention.

PURPOSE The purpose of this study was to investigate the effect of resin cements and primer on the retentive force of zirconia copings bonded to zirconia abutments with insufficient retention. MATERIALS AND METHODS Zirconia blocks (Lava, 3M ESPE, St. Paul, MN, USA) were obtained and forty sets of zirconia abutments and copings were fabricated using CAD/CAM technology. They were grouped into 4 categories as follows, depending on the types of resin cements used, and whether the primer is applied or not:Panavia F2.0 (P), Panavia F2.0 using Primer (PRIME Plus, Bisco Inc, Schaumburg, IL, USA) (PZ), Superbond C&B (S), and Superbond C&B using Primer (SZ). For each of the groups, the cementation was conducted. The specimens were kept in sterilized water (37℃) for 24 hours. Retentive forces were tested and measured, and a statistical analysis was carried out. The nature of failure was recorded. RESULTS The means and standard deviations of retentive force in Newton for each group were 265.15 ± 35.04 N (P), 318.21 ± 22.24 N (PZ), 445.13 ± 78.54 N (S) and 508.21 ± 79.48 N (SZ). Superbond C&B groups (S & SZ) showed significantly higher retentive force than Panavia F2.0 groups (P & PZ). In Panavia F2.0 groups, the use of primer was found to contribute to the increase of retentive force. On the other hand, in Superbond C&B groups, the use of primer did not influence the retention forces. Adhesive failure was observed in all groups. CONCLUSION This study suggests that cementation of the zirconia abutments and zirconia copings with Superbond C&B have a higher retentive force than Panavia F2.0. When using Panavia F2.0, the use of primer increases the retentive force.

The effect of microgrooves on osseointegration of titanium surfaces in rabbit calvaria

The purpose of this study was to evaluate bone formation ability and bone-implant adhesion over time when microgrooves are present on the surface of cylindrical titanium implants. Eight New Zealand White rabbits with a weight of approximately 3.5 kg were used. Cylindrical titanium implants with a smooth surface (NE0), acidetched rough surface (E0), and microgroove surface (NE60/10) were placed in each rabbit’s skull, with one implant of each type placed in each skull. Experimental animals were sacrificed after 2 and 4 weeks, and tissue specimens were processed for histomorphometric analysis of bone formation by measuring bone-implant contact (BIC) and the degree of differentiation. The bone-implant contact ratio at 2 and 4 weeks was 15.9% and 29.6% (NE0), 15.6% and 34.5% (E0), and 15.3% and 52.7% (NE60/10), respectively. Good bone regeneration was observed in all experimental groups; at 4 weeks, in particular, the NE60/10 group showed high bone contact relative to the control group (p < 0.05), and other groups showed stable and mature bone. On the basis of the observed increase in bone-implant adhesion at the titanium surface, microgrooves with a width of 60 μm and depth of 10 μm are considered to promote implant osseointegration.

Design of new prosthetic leg damper for above knee amputees using a magnetorheological damper activated permanent magnet only

Magnetorhological fluids (MR) have been applied to numerous devices or systems which require forward or feedback control to achieve desired performances. One of applications is the rehabilitation device. MR dampers applied to artificial joints are implemented with two phases; stance phase: motion to support the feet on the ground, and swing phase : motion to step out. In case of stance phase, the damping force should be increased by applying the magnetic field to support the body. On the other hand, in case of swing phase, the damping force should be removed by not applying the magnetic field so that the prosthesis can be easily rotated by the motor. In this study, a special mechanism of MR damper is proposed to make a prosthetic leg which can derive on/off mode using permanent magnet only. The design mechanism is undertaken and damping force is analyzed to validate the effectiveness of the proposed damper system for the patient’s motion without control device.

Process design for solution growth of SiC single crystal based on multiphysics modeling

*Energy and Environmental Division,Korea Institute of Ceramic Engineering and Technology, Jinju 52851, Korea**Department of Chemical and Biomolecular Engineering, Yonsei University, Seoul 03722, Korea(Received November 20, 2015)(Revised November 30, 2015)(Accepted December 7, 2015)Abstract A top-seeded solution growth (TSSG) is a method of growing SiC single crystal from the Si melt dissolved thecarbon. In this study, multiphysics modeling was conducted using COMSOL Multiphysics, a commercialized finite elementanalysis package, to get analytic results about electromagnetic analysis, heat transfer and fluid flow in the Si melt.Experimental results showed good agreements with simulation data, which supports the validity of the simulation model.Based on the understanding about solution growth of SiC and our set-up, crystal growth was conducted on off-axis 4H-SiCseed crystal in the temperature range of 1600~1800