• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2016년도 추계학술대회 논문집
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• pp.153-153
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• 2016

Aluminum alloys have poor corrosion resistance compared to the pure aluminum due to the additive elements. Thus, anodizing technology artificially generating thick oxide films are widely applied nowadays in order to improve corrosion resistance. Anodizing is one of the surface modification techniques, which is commercially applicable to a large surface at a low price. However, most studies up to now have focused on its commercialization with hardly any research on the assessment and improvement of the physical characteristics of the anodized films. Therefore, this study aims to select the optimum temperature of sulfuric electrolyte to perform excellent corrosion resistance in the harsh marine environment through electrochemical experiment in the sea water upon generating porous films by variating the temperatures of sulfuric electrolyte. To fabricate uniform porous film of 5083 aluminum alloy, we conducted electro-polishing under the 25 V at $5^{\circ}C$ condition for three minutes using mixed solution of ethanol (95 %) and perchloric (70 %) acid with volume ratio of 4:1. Afterward, the first step surface modification was performed using sulfuric acid as an electrolyte where the electrolyte concentration was maintained at 10 vol.% by using a jacketed beaker. For anode, 5083 aluminum alloy with thickness of 5 mm and size of $2cm{\times}2cm$ was used, while platinum electrode was used for cathode. The distance between the two was maintained at 3 cm. Afterward, the irregular oxide film that was created in the first step surface modification was removed. For the second step surface modification process (identical to the step 1), etching was performed using mixture of chromic acid (1.8 wt.%) and phosphoric acid (6 wt.%) at $60^{\circ}C$ temperature for 30 minutes. Anodic polarization test was performed at scan rate of 2 mV/s up to +3.0 V vs open circuit potential in natural seawater. Surface morphology was compared using 3D analysis microscope to observe the damage behavior. As a result, the case of surface modification presented a significantly lower corrosion current density than that without modification, indicating excellent corrosion resistance.

• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2016년도 추계학술대회 논문집
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• pp.198-198
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• 2016

An ideal orthopedic implant should provide an excellent bone-implant connection, less implant loosening and minimum adverse reactions. Commercial pure titanium (CP-Ti) and Ti alloys have been widely utilized for biomedical applications such as orthopedic and dental implants. However, being bioinert, the integration of such implant in bone was not in good condition to achieve improved osseointegraiton, there have been many efforts to modify the composition and topography of implant surface. These processes are generally classified as physical, chemical, and electrochemical methods. Plasma electrolytic oxidation (PEO) as an electrochemical route has been recently utilized to produce this kind of composite coatings. Mg ion plays a key role in bone metabolism, since it influences osteoblast and osteoclast activity. From previous studies, it has been found that Mg ions improve the bone formation on Ti alloys. PEO is a promising technology to produce porous and firmly adherent inorganic Mg containing $TiO_2$($Mg-TiO_2$ ) coatings on Ti surface, and the amount of Mg introduced into the coatings can be optimized by altering the electrolyte composition. In this study, a series of $Mg-TiO_2$ coatings are produced on Ti-6Al-4V ELI dental implant using PEO, with the substitution degree, respectively, at 0, 5, 10 and 20%. Based on the preliminary analysis of the coating structure, composition and morphology, a bone like apatite formation model is used to evaluate the in vitro biological responses at the bone-implant interface. The enhancement of the bone like apatite forming ability arises from $Mg-TiO_2$ surface, which has formed the reduction of the Mg ions. The promising results successfully demonstrate the immense potential of $Mg-TiO_2$ coatings in dental and biomaterials applications.

• Restorative Dentistry and Endodontics
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• 제38권4호
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• pp.210-214
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• 2013

Objectives: This study aimed to evaluate the capacity of 2% chlorhexidine gel associated with 8% papain gel in comparison with 5.25% sodium hypochlorite in bovine pulp tissue dissolution. Materials and Methods: Ninety bovine pulps of standardized sizes were used and fragmented into 5-mm sizes. The fragments were removed from the root middle third region. They were divided into 6 experimental groups (n = 15), 1) 8% papain; 2) 2% chlorhexidine; 3) 2% chlorhexidine associated with 8% papain; 4) 0.9% saline solution; 5) 2.5% sodium hypochlorite; and 6) 5.25% sodium hypochlorite. The pulp fragments were weighed and put into immobile test tubes for dissolution for time intervals of 30, 60, 90, and 120 min. Results: The 5.25% sodium hypochlorite had greater dissolution potential than the pure papain, and when associated with chlorhexidine, both promoted greater dissolution than did the saline solution and 2% chlorhexidine groups (p < 0.05). The 2.5% sodium hypochlorite promoted dissolution to a lesser extent than the groups with papain within a period of 30 min (p < 0.05), but, was comparable to the saline solution and chlorhexidine. After 120 min, the 2.5% and 5.25% sodium hypochlorite promoted dissolution of 100% of the pulp fragments, and papain, 61%, while chlorhexidine associated with papain and chlorhexidine alone dissolved only 55% and 3%, respectively. Conclusions: The 8% papain in gel, both alone and in association with chlorhexidine, was able to dissolve bovine pulp tissue, but to a lesser extent than did 5.25% sodium hypochlorite.

• 산업경영시스템학회지
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• 제41권3호
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• pp.61-71
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• 2018

The purpose of this study is to analyze the efficiencies of project management offices in large information system construction projects using the data envelopment analysis. In addition, we tried to estimate the confidence interval of those efficiencies using bootstrap DEA to give a statistical meaning. The efficiency by the CCR model is analyzed as eight project management offices are fully efficient and 22 project management offices are inefficient. On the other hand, there are 15 project management offices are fully efficient, but 15 project management offices are inefficient in the BCC model. As the result of the scale efficiencies, of the inefficient project management offices, 13 project management offices are inefficient in scale. It is possible to eliminate the inefficiency in the CCR model by improving their project performances. And, the nine project management offices showed that the inefficiency was due to pure technical efficiency, and these companies should look for various improvements such as improvement of project execution system and project management process. In order that the inefficient project management offices be efficient, it is analyzed that more efforts must be made for on-budget and on-time as a result of examining the potential improvement potentials of inefficient project management offices.

• 동아시아식생활학회지
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• 제20권6호
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• pp.947-956
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• 2010

The purpose of this study was to synthesize tasty and healthy solomon's seal coffee by combining solomon's seal and a coffee-making process. Therefore, this study was carried out to establish the most suitable conditions for coffee-making by surface response surface methodology. Using the center synthesis method, we synthesized solomon's seal coffee by considering three factors (solomon's seal, coffee, and temperature) and three levels. The sixteen experimental items for solomon's seal coffee based on surface-reaction analysis were scent (crust break-scent when pouring water in solomon's seal coffee, flavorscent when tasting solomon's seal coffee), taste (clean-cup-pure taste without loose scent, sweetness, and acidity), mouth-feel, aftertaste, overall quality, and other taste degrees. Scores were from 1 to 7, with 7 indicating the highest preference. The optimum mixing rates which meet sensory items were coffee 19.51g, solomon's seal 2.07g, and temperature $93.39^{\circ}C$. Based on the above results, solomon's seal seems to be well suited for coffee. It was also found that solomon's seal has great potential to be well suited with other foods.

• 대한화학회지
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• 제21권2호
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• pp.75-82
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• 1977

순수한 액체의 증가압에 미치는 동위원소 효과를 연구하였고, 증기압 비를 계산하였다. Significant Structure Theory of Liquid를 사용한 계산결과에 의하면, $C_2H_4/C_2H_2D_2$(trans)계 에서는 분자량과 관성능률에 의한 효과가 현저하고, $C_2H_2D_2(trans)/C_2H_2D_2(cis)$계에서는 분자 회전이 자유롭지 못한 데서 오는 영점에너지 효과가 현저했다. 그리고, $CH_3OH/CH_3OD$계에서는 분자간 인력이 동위원소에 따라 다르기 때문임이 밝혀졌다. $CH_4/CD_4,\;SiH_4/SiD_4,\;GeH_4/GeD_4$ 동위원소계에서는 분자량에 의한 효과가 $CH_4/CD_4 >SiH_4/SiD_4 >GeH_4/GeD_4$의 순서로 감소함을 알 수 있었다.

• Elastomers and Composites
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• 제42권3호
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• pp.177-185
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• 2007

유기화된 montmorillonite(O-MMT)와 인을 포함하는 polyamic acid(PPAA)를 용액 블렌딩하여 PAA/organoclay 나노 복합체를 제조하였다. 이들 나노 복합체들의 연구를 위하여 FT-IR, DSC, TGA, PCFC, SEM 그리고 XRD를 이용하였다. 나노복합체들의 제조확인은 FT-IR과 XRD 분석을 통하여 확인하였다. SEM 사진들은 O-MMT가 매트릭스 고분자에 비교적 고르게 분산되어 있음을 보여 주었고, XRD 결과를 통하여 O-MMT가 intercalation 되었음을 확인하였다. O-MMT/PPAA 나노복합체들의 열안정성 및 난연성은 순수한 PAA 보다 크게 높았으며, O-MMT/PPAA-0.2, 0.4, 0.6 복합체들의 열방출 용량과 총열방출 값들은 인의 함량 증가와 함께 감소하였다. 본 연구에서 제조된 나노복합체 필름들이 화재안전재료로서 사용될 수 있는 잠재성을 가지고 있음을 확인하였다.

• 한국재료학회지
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• 제24권1호
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• pp.19-24
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• 2014

We report the nitrogen monoxide (NO) gas sensing properties of p-type CuO-nanorod-based gas sensors. We synthesized the p-type CuO nanorods with breadth of about 30 nm and length of about 330 nm by a hydrothermal method using an as-deposited CuO seed layer prepared on a $Si/SiO_2$ substrate by the sputtering method. We fabricated polycrystalline CuO nanorod arrays at $80^{\circ}C$ under the hydrothermal condition of 1:1 morality ratio between copper nitrate trihydrate [$Cu(NO_2)_2{\cdot}3H_2O$] and hexamethylenetetramine ($C_6H_{12}N_4$). Structural characterizations revealed that we prepared the pure CuO nanorod array of a monoclinic crystalline structure without any obvious formation of secondary phase. It was found from the gas sensing measurements that the p-type CuO nanorod gas sensors exhibited a maximum sensitivity to NO gas in dry air at an operating temperature as low as $200^{\circ}C$. We also found that these CuO nanorod gas sensors showed reversible and reliable electrical response to NO gas at a range of operating temperatures. These results would indicate some potential applications of the p-type semiconductor CuO nanorods as promising sensing materials for gas sensors, including various types of p-n junction gas sensors.

• 설비공학논문집
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• 제21권9호
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• pp.505-512
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• 2009

A thermosiphon is utilized as a thermal shunt to reduce the cool-down time of a cryogenic system cooled by a two stage cryocooler. The cool-down time reduction by the thermosiphon is determined by the type of working fluid which is directly related to the operating temperature range of the thermosiphon. A mixed working fluid has a potential to widen the operation temperature range of the thermosipohon. In this study, the thermosiphon using N$_2$ and CF$_4$ mixture as the working fluid is fabricated and tested to verify its transient heat transfer performance. The thermosiphon with the mixed working fluid has no noticeable reduction of cool-down time compared with that of the thermosiphon with pure working fluid in this experiment. However, it seems that the thermosiphon with mixed working fluid may have an advantage according to the cooling capacity of a cryocooler, the cooling target temperature and the size of a cooling object.

• 한국재료학회지
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• 제25권10호
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• pp.566-570
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• 2015

$Bi_{0.5}Na_{0.5}TiO_3$ (BNT) based ceramics are considered potential lead-free alternatives for $Pb(Zr,Ti)O_3$(PZT) based ceramics in various applications such as sensors, actuators and transducers. However, BNT-based ceramics have lower electromechanical performance as compared with PZT based ceramics. Therefore, in this work, lead-free bulk $0.99[(Bi_{0.5}Na_{0.5})_{0.935}Ba_{0.065}]_{(1-x)}La_xTiO_3-0.01SrZO_3$ (BNBTLax-SZ, with x = 0, 0.01, 0.02) ceramics were synthesized by a conventional solid state reaction The crystal structure, dielectric response, degree of diffuseness and electric-field-induced strain properties were investigated as a function of different La concentrations. All samples were crystallized into a single phase perovskite structure. The temperature dependent dielectric response of La-modified BNBT-SZ ceramics showed lower dielectric response and improved field-induced strain response. The field induced strain increased from 0.17%_for pure BNBT-SZ to 0.38 % for 1 mol.% La-modified BNBT-SZ ceramics at an applied electric field of 6 kV/mm. These results show that La-modified BNBT-SZ ceramic system is expected to be a new candidate material for lead-free electronic devices.