• Journal of the Korean Society for Precision Engineering
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• v.26 no.11
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• pp.131-137
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• 2009

A pair of connectors for transferring torque is widely used in various types of a mechanical system. By the repetition of mechanical contact between a pair of connector, wear occurs easily. This kind of defect sometimes can cause a serious problem of health in case of the connector is used in a refrigerator. In this work, the material combination of connectors was experimentally studied to reduce the amount of wear; for the combination of connectors, various types of engineering materials including polyacetal, polycabonate, stainless steel (STS-304), NiP coated STS-304, and STS-310 were evaluated to check each wear behavior. Also an effective method of wear test was suggested for precise controlling of wear conditions such as contact area, contact force, and relative motion speed. From the test results, it was found out that a pair of polyacetal to STS-304 and STS-310 showed the lowest specific wear rates among other pairs.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.07a
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• pp.251-254
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• 2001

This paper describes an efficiency improvement of buried contact solar cell (BSCS) with a structure of MgF$_2$/CeO$_2$/Ag/Cu/Ni grid/n$^{+}$ emitter/p-type Si base/p$^{+}$/Al. Theoretical and experimental investigations were performed on a double layer antireflection (DLAR) coating of MgF$_2$/CeO$_2$. We investigated CeO$_2$ films as an AR layer because they have a proper refractive index of 2.46 and demonstrate the same lattice constant as Si substrate. An optimized DLAR coating shewed a reflectance as low as 2.04 % in the wavelengths ranged from 0.4 ${\mu}{\textrm}{m}$ to 1.1 ${\mu}{\textrm}{m}$. BCSC cell efficiency was improved from 16.2 % without any AR coating to 19.9 % by employing DLAR coatings. Further details on MgF$_2$/CeO$_2$ DLAR coatings on the BCSC cells are presented in this paper.per.

• Journal of Periodontal and Implant Science
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• v.43 no.6
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• pp.291-300
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• 2013

Purpose: Calcium phosphate (CaP)-coated implants promote osseointegration and survival rate. The aim of this study was to (1) analyze the dissolution behavior of the residual CaP particles of removed implants and (2) evaluate bone apposition of CaP-coated machined surface implants at the early healing phase. Methods: Mandibular premolars were extracted from five dogs. After eight weeks, the implants were placed according to drilling protocols: a nonmobile implant (NI) group and rotational implant (RI) group. For CaP dissolution behavior analysis, 8 implants were removed after 0, 1, 2, and 4 weeks. The surface morphology and deposition of the coatings were observed. For bone apposition analysis, block sections were obtained after 1-, 2-, and 4-week healing periods and the specimens were analyzed. Results: Calcium and phosphorus were detected in the implants that were removed immediately after insertion, and the other implants were composed mainly of titanium. There were no notable differences between the NI and RI groups in terms of the healing process. The bone-to-implant contact and bone density in the RI group showed a remarkable increase after 2 weeks of healing. Conclusions: It can be speculated that the CaP coating dissolves early in the healing phase and chemically induces early bone formation regardless of the primary stability.

• Journal of Microbiology and Biotechnology
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• v.33 no.7
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• pp.895-908
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• 2023

Disposal of waste containing heavy metals into the environment is a major threat to human health and can result in toxic or chronic poisoning in aquatic life. In the current study, metal-resistant Raoultella ornithinolytica was isolated from metal-contaminated samples collected from the Tanjaro River, located southwest of Sulaymaniyah, Iraq. R. ornithinolytica was identified by partial amplification of 16S rRNA. The uptake potency of heavy metals was assessed using inductively coupled plasma-optical emission spectroscopy (ICP-OES) and indicated that R. ornithinolytica removed 67, 89, 63.4, 55.6, 56.5, 65, and 61.9% of Cd, Pb, Cr, Ni, Zn, Co, and Fe, respectively. These removal rates were influenced by temperature, pH, and contact time; at 35℃ and pH 5 with a change in the incubation time, the reduction rate improved from 89 to 95% for Pb, from 36.4 to 45% for Cu, and from 55.6 to 64% for Ni. Gene analysis indicated that R. ornithinolytica contained pbrT, chrB, nccA, iroN, and czcA genes, but the pcoD gene was absent. Energy-dispersive X-ray spectroscopy (EDS) images showed evidence of metal ion binding on the cell wall surface with different rates of binding. Transmission electron microscopy (TEM) detected different mechanisms for metal particle localization; cell surface adsorption was the main mechanism for Pb, Zn, and Co uptake, while Cd, Ni, and Fe were accumulated inside the cell. The current study describes, for the first time, the isolation of R. ornithinolytica from metal-contaminated water, which can be used as an eco-friendly biological expedient for the remediation and detoxification of metals from contaminated environments.

• Advances in nano research
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• v.12 no.5
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• pp.457-465
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• 2022

The potentials of Ni_xZn_1-xFe₂O₄ (x = 0.0, 0.2, 0.4, 0.6, 0.8 and 1.0) nanoadsorbents were investigated for removal of Cd and Cr from contaminated water from an electroplating industry in Himachal Pradesh, India. Optimal values were recorded under batch adsorption experiments performed to remove dissolved heavy metal ions from industrial wastewater. The specific surface area (SSA) of nanoadsorbents perceived to vary in a range 35.75-45.29 cm²/g and was calculated from the XRD data. The influence of two operating parameters, contact time and dopant (Ni) concentration was also investigated at pH ~7 with optimum dosage. Kinetic studies were conducted within a time range of 2-10 min with rapid adsorption of cadmium and chromium ions onto Ni_0.2Zn_0.8Fe₂O₄ nanoadsorbents. Pseudo-second-order kinetic model was observed to be well fitted with the adsorption data that confirmed the only existence of chemisorption throughout the adsorption process. The maximum adsorption efficiency values observed for Cd and Cr were 51.4 mg/g and 40.12 mg/g, respectively for different compositions of prepared series of nanoadsorbents. The removal percentage of Cd and Cr was found to vary in a range of 47.7%-95.25% and 21%-50% respectively. The prepared series of nanoferrite found to be suitable enough for adsorption of both heavy metal ions.

• Proceedings of the Korean Vacuum Society Conference
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• 2000.02a
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• pp.116-116
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• 2000

질화물 반도체는 LED, LD, Transistor, 그리고 Photodetector 등 광소자 및 전자소자를 실현할 수 있는 소재로써 최근에 각광 받고 있으며, 또한 국·내외적으로 연구가 활발히 진행되고 잇다. 질화물 발광 다이오드 제작에는 소자의 효율과 수명시간의 향상을 위하여 질화물 반도체와 금속과의 접합시 고 품질의 오믹 접합이 필수적이다. 특히 p-형 GaN의 경우에는 높은 정공 농도를 갖는 p-형 GaN를 얻기가 어렵고 GaN의 일함수에 비하여 높은 일함수를 갖는 금속이 없기 때문에 매우 낮은 접합 저항을 가지며 안정성이 매우 우수한 금 접합을 얻기가 어렵다고 알려져 있다. 또한, GaN 계열의 발광 다이오드는 일반적으로 표면 발광 다이오드 형태로 제작되기 때문에 p-형 GaN 층의 오믹 접촉으로 사용되는 금속의 전기적 특성뿐만 아니라 발광 다이오드의 활성층에서 발광되어 나오는 빛에 대한 투과도 또한 우수하여야 발광 다이오드의 효율이 우수해진다. 본 연구에서는 p-형 GaN층의 접합 금속으로 Pt(80nm)과 Ni(5nm)/Au(7nm)를 사용하여 InGaN/GaN 다중양자우물 구조의 발광 다이오드를 제작하여 전기적 특성 및 발광효율을 측정하였다. 그리고, Pt(80nm)과 p-형 GaN와의 접합시 온도 변화에 따른 전기적 특성을 TLM 방법으로 조사하고, 가시광선 영역에서의 빛에 대한 투과도를 UV/VIS spectrometer, X-ray reflectivity, 그리고 Atomic Force Microscopy 등을 이용하여 분석하였다.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.11a
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• pp.150-150
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• 2008

본 연구에서는 Wet chemistry damage가 Nanopatterned p-ohmic electrode에 미치는 영향을 연구하였다. Nanopattern은 Metal clustering을 이용하여, P-GaN와 Ohmic형성에 유리한 Pd을 50$\AA$ 적층한 후 Rapid Thermal Annealing방법으로 $850^{\circ}C$, $N_2$분위기에서 3min열처리를 하여 Pd Clustering mask 를 제작하였다. Wet etching은 $85^{\circ}C$, $H_3PO_4$조건에서 시간에 따라 Sample을 Dipping하는 방법으로 시행하였다 Ohmic test를 위해서 Circular - Transmission line Model 방법을 이용하였으며, Atomic Force Microscopy과 Parameter Analyzer로 Nanopatterned GaN surface위에 형성된 Ni/ Au Contact에서의 전기적 분석과, 표면구조분석을 시행하였다. AFM결과 Wet처리시간에 따라서 Etching형상 및 Etch rate이 영향을 받는 것이 확인되었고, Ohmic test에서 Wet chemistry처리에 의한 Tunneling parameter와 Schottky Barrier Height가 크게 증/감함을 관찰하였다. 이러한 결과들은 Wet처리에 의해서 발생된 Defect가 GaN의 표면과 하부에서 발생되며, Deep acceptor trap 및 transfer거동과 밀접한 관련이 있음을 확인 할 수 있었다. 보다 자세한 Transport 및 Wet chemical처리영향에 관한 형성 Mechanism은 후에 I-V-T, I-V, C-V, AFM결과 들을 활용하여 발표할 예정이다.

• Journal of the Korean Chemical Society
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• v.57 no.3
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• pp.316-321
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• 2013

Electrocoagulation (EC) technique is applied for the treatment of wastewater containing heavy metals ions such as nickle (Ni), lead (Pb) and cadmium (Cd) by using sacrificial anodes corrode to release active coagulant flocs usually aluminium or iron cations into the solution. During electrolytic reactions hydrogen gas evolve at the cathode. All the experiments were carried out in Batch mode. The tank was filled with synthetic wastewater containing heavy metals and efficiency of electro-coagulation in combination with aluminum and iron electrodes were investigated for removal of such metals. Several parameters, such as contact time, pH, electro-coagulant concentration, and current density were optimized to achieve maximum removal efficiency (%). The concentrations of heavy metals were determined by using Atomic Absorption Spectroscopy (AAS). It is found that the electro-coagulation process has potential to be utilized for the cost-effective removal of heavy metals from wastewater specially using iron electrodes in terms of high removal efficiencies and operating cost.

• Journal of the Korean Society for Precision Engineering
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• v.29 no.4
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• pp.409-416
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• 2012

Recently, surface modification technology is of importance to improve the wear resistance and the corrosive resistance for high accurate mechanical parts such as LM guide, Ball Screw and Roller Bearing etc., Those has generally featured on rolling contact mechanism to improve not only the wear and the friction, but also the accuracy and the corrosion performances. For surface modifications of high accurate mechanical parts, normally thermal spray, PVD, CVD and E.P. processes have been used with many materials such as DLC, raydent, W, Ni, Ti etc. Diamondlike carbon (DLC) films possess a combination of attractive properties and have been largely employed to modify the tribological behaviors such as friction, wear, corrosion, fretting fatigue, biocompatibility, etc. However, for rolling contact mechanism mechanical parts DLC films are needed to study for commercial benefit. Rolling contact mechanism has features on effects of cyclic motions and stresses, and also not simply sliding motions. The papers focused on the performance test of wear and corrosive resistance according to Me-DLC film thickness. And also, its thickness effect of wear analysis was carried out through the simulation of the maximum shear stress under the rolling contact surface. As the results, Me-DLC films have more potential to improve the wear resistance for high precision mechanical parts than raydent films.

• The korean journal of orthodontics
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• v.43 no.3
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• pp.120-126
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• 2013

Objective: To gain basic information regarding the biologic stability of plasma ion-implanted miniscrews and their potential clinical applications. Methods: Sixteen plasma ion-implanted and 16 sandblasted and acid-etched (SLA) miniscrews were bilaterally inserted in the mandibles of 4 beagles (2 miniscrews of each type per quadrant). Then, 250 - 300 gm of force from Ni-Ti coil springs was applied for 2 different periods: 12 weeks on one side and 3 weeks contralaterally. Thereafter, the animals were sacrificed and mandibular specimens including the miniscrews were collected. The insertion torque and mobility were compared between the groups. The bone-implant contact and bone volume ratio were calculated within 800 mm of the miniscrews and compared between the loading periods. The number of osteoblasts was also quantified. The measurements were expressed as percentages and analyzed by independent t-tests (p < 0.05). Results: No significant differences in any of the analyzed parameters were noted between the groups. Conclusions: The preliminary findings indicate that plasma ion-implanted miniscrews have similar biologic characteristics to SLA miniscrews in terms of insertion torque, mobility, bone-implant contact rate, and bone volume rate.