• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.11
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• pp.5377-5384
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• 2013

This paper presents the effects of the tube materials and corrosion on the heat transfer performance of double-tube heat exchangers for the development of heat exchangers using deep sea water. Heat exchangers made of titanium, aluminum. stainless steel, iron, copper, and aluminum with electro-deposition coatings(Carbon black_$15{\mu}m$, Carbon black_$150{\mu}m$) were tested. Also, the heat transfer rate of each heat exchanger was calculated by using EES program. For the acceleration of corrosion by sea water, the temperature of sea water $70^{\circ}C$ and the concentration of salt 3.5% were considered. And the specimens were immersed in sea water during 6 weeks. From the above experiment and analysis, aluminum with electro-deposition coating(Carbon black_$150{\mu}m$) can be considered the most promising candidate for the replacement of titanium heat exchanger.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.200-200
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• 2012

We investigated a flexible transparent film using the spinning multi-walled carbon nanotubes (MWCNTs). Spin-capable MWCNTs on iron catalyzed on a SiO2 wafer was grown by chemical vapor deposition, which was performed at $780^{\circ}C$ using C2H2 and H2 gas. The average diameter and length of MWCNTs grown on the substrate were ~15 nm and $250{\sim}300{\mu}m$, respectively. The MWCNT sheets were produced by continuously pulling out from well-aligned MWCNTs on a substrate. The MWCNT sheet films were produced simply by direct coating on the flexible film or grass. The thickness of sheet film was remarkably decreased by alcohol spraying on the surface of sheet. The alcohol splay increased transmittance and decreased electrical resistance of MWCNT sheet films. Single and double sheets were produced with sheet resistance of ~699 and ${\sim}349{\Omega}/sq$, respectively, transmittance of 81~85 % and 67~72%, respectively. The MWCNT sheet films were heated through the application of direct current power. The flexible transparent heaters showed a rapid thermal response and uniform distribution of temperature. In addition, MWCNT yarns were prepared by spinning a bundle of MWCNTs from vertically super-aligned MWCNTs on a substrate, and field emission from the tip and side of the yarns was induced in a scanning electron microscope. We found that the field emission behavior from the tip of the yarn was better than the field emission from the side. The field emission turn-on voltages from the tip and side of MWCNT yarns were 1.6 and $1.7V/{\mu}m$, respectively, after the yarn was subjected to an aging process. Both the configuration of the tip end and the body of the yarn were changed remarkably during the field emission. We also performed the field emission of the sheet films. The sheet films showed the turn on voltage of ${\sim}1.45V/{\mu}m$ during the field emission.

• Korean Journal of Materials Research
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• v.13 no.6
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• pp.389-393
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• 2003

The effect of antireflection layer on the reduction of optical loss has been investigated in Si photodiodes detecting red light with central wavelength of 670 nm. The theoretical analysis showed minimum reflection loss of 6% for the $SiO_2$thickness of about $1100∼1200\AA$ in the $SiO_2$-Si system with the single antireflection layer and no reflection loss for the X$N_3$N$_4$$SiO_2$thickness of $2000\AA$/$1200\AA$ in the $Si_3$$N_4$$SiO_2$-Si system with double antireflection layer. In our experiments, Si photodiodes with the web-patterned $p^{＋}$-shallow diffusion region were fabricated by bipolar IC process technology and the devices were classified into three kinds according to the structure of $Si_3$$N_4$/$SiO_2$antireflection layer. The fabricated devices showed maximum spectral response in the optical spectrum of 650∼700 nm. The average photocurrents of the devices with the $Si_3$$N_4$$SiO_2$thickness of $1000\AA$/X$SiO\AA$, and $2000\AA$$1800\AA$ under the incident power, of -17 dBm were 3.2 uA, 3.5 uA and 3.1 uA, respectively.

• The Journal of Korean Academy of Prosthodontics
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• v.40 no.6
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• pp.590-596
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• 2002

The resin : metal interface is at the basis of most bonding failures in resin-bonded prosthesis. Although debonding has been a problem with adhesive fixed partial dentures, various dentists classify them as long-term restorations. The advantages of resin-bonded fixed partial dentures include minimal tooth reduction and the possibility of rebonding. if resin-bonded protheses can be easily rebounded, it is of clinical importance to know if the lutingagents rebond as well the second time as they did originally. Several retentive systems for resin-to-metal bonding have recommended. Treatments such as electrolytic etching and silicone coating, despite the good result of bond strength, have proved to be time-consuming and technique-sensitive. Therefore a simple and more reliable method is desirable. This study evaluated the effect of metal surface treatments on the rebond strength of panavia 21 cement to a nickel-chromium(Ni-Cr) alloy. The samples were received the following surface treatments : Group No.1 (control or served as the control) treatment with sandblasting with 50um aluminum oxide and ultrasonically cleaned for 10minutes in double-deionized water, Group No.2 were no surface treatments. Group No.3 were treated with metal primer. Group No.4 were treated with sandblasting as previously described, and then metal priming. From the analysis of the results, the following conclusions were drawn. 1. Sandblasting and metal priming appears to be an effective method for treatment of metal after accidental debonding. 2. Group without surface treatment had significantly lower bond strengths compared with other groups. 3. The combination of sandblasting and metal priming may not develop superior bonding strengths compared with other techniques that used the Ni-Cr alloys. 4. Combination of cohesive and adhesive failures were the most common type observed. The results support the use of sandblasting as a viable procedure when rebonding accidentally lost adhesive partial denture. We concluded that sandblasting and metal priming of metal surface before bonding could provide the adequate bond strength during rebonding of resin-bonded fixed partial denture.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.525-528
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• 2008

For well-constructed concrete, its service life is a long term and it has an enough durability performance. However, for cracked concrete, it is clear that cracks should be preferential channel for the penetration of aggressive substance such as chloride ions according to author's previous researches. In order to enhance the lifetime of cracked concrete, critical issues in the performance of the concrete is the risk of chloride-induced corrosion. Even though crack width can be reduced due to the high reinforcement ratio, the question is to which extend these cracks may jeopardize the durability of cracked concrete. If the size of crack is small, surface treatment system can be considered as one of the best options to extend the service life of concrete structures exposed to marine environment simply in terms of cost effectiveness versus durability performance. Thus, it should be decided to undertake an experimental study on the effect of different types of surface treatment system, which are expected to seal the concrete and the cracks to chloride-induced corrosion in particular. In this study, it is examined the effect of surfaced treated systems on chloride penetration through microcracks. Single surface treatments of penetrant or coating and double application were considered as an experimental variation. RCM (Rapid Chloride Migration) testing is accomplished to visualize chloride penetration via cracks.

• Korean Journal of Optics and Photonics
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• v.20 no.5
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• pp.276-280
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• 2009

A Cr:YAG crystal was used as a saturable absorber for passive Q-switching of a Nd:$YVO_4$ laser which was pumped by a 1-W continuous wave laser diode. The first surface of the Cr:YAG was high-reflection coated for the pump wavelength. The high-reflection coating improved the absorption efficiency of the pump beam in the Nd:$YVO_4$ through double pass absorption. It also prevented pump beam induced partial bleaching of the Cr:YAG. The peak-to-peak pulse fluctuation of passively Q-switched laser output was approximately 4 %. The minimum pulse-width was measured to be 7.11 ns. Also, the average pulse repetition rate was 9 kHz and the maximum output power was 16.27 mW.

• Resources Recycling
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• v.28 no.1
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• pp.3-14
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• 2019

Copper is used in many electronic components and construction parts due to its excellent electrical conductivity and heat transfer characteristics, and also used for pre-plating for double layer coating such as nickel, so that copper is an essential material in modern industry. Despite the expected increase of usage and importance on wiring, sensors and data equipment in the next generation industries, it is hard for securing stable copper supply and resource management resulting from the copper prices are fluctuating owing to the economic crisis in Europe, the low economic growth trend in China, and President Trump's commitment to public industrial facilities investment in U.S.. Since most of the domestic copper consumption is used by electrolytic copper cathode, we studied not only copper recycling technology which is being commercialized but also current research trend under the research stage. This study aims to examine the characteristics of each process and the areas where future recycling technology development is required.

• Korean Journal of Materials Research
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• v.32 no.9
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• pp.384-390
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• 2022

A spin coating process for RRAM, which is a TiN/TiO₂/FTO structure based on a PTC sol solution, was developed in this laboratory, a method which enables low-temperature and eco-friendly manufacturing. The RRAM corresponds to an OxRAM that operates through the formation and extinction of conductive filaments. Heat treatment was selected as a method of controlling oxygen vacancy (V_O), a major factor of the conductive filament. It was carried out at 100 ℃ under moisture removal conditions and at 300 ℃ and 500 ℃ for excellent phase stability. XRD analysis confirmed the anatase phase in the thin film increased as the heat treatment increased, and the Ti³⁺ and OH- groups were observed to decrease in the XPS analysis. In the I-V analysis, the device at 100 ℃ showed a low primary SET voltage of 5.1 V and a high ON/OFF ratio of 10⁴. The double-logarithmic plot of the I-V curve confirmed the device at 100 ℃ required a low operating voltage. As a result, the 100 ℃ heat treatment conditions were suitable for the low voltage driving and high ON/OFF ratio of TiN/TiO₂/FTO RRAM devices and these results suggest that the operating voltage and ON/OFF ratio required for OxRAM devices used in various fields under specific heat treatment conditions can be compromised.

• Journal of the Korean Electrochemical Society
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• v.17 no.1
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• pp.37-43
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• 2014

In this study, capacitive deionization (CDI) was introduced for desalination of mining water. Ion-exchange polymer coated carbon electrodes (IEE) were used in CDI to desalt mining water. The CDI performance using the IEE for desalination of mining water was carried out and then was compared with that using general carbon electrodes without ion-exchange polymer coating (GE). Moreover, to investigate the effect of the concentration of influent solutions on CDI performance, the CDI performance using the IEE for desalination of brackish water (NaCl 200 ppm) was also performed and analyzed. As a result, the higher salt removal efficiency, rate and the lower energy consumption in the CDI process using the IEE and mining water were obtained compared with those using the GE and mining water. It is mainly due to higher non-Faradaic current, low ohmic resistance of the influent, overlapping effect of electric double layers in micropore of the electrode. In addition, the CDI process using the IEE and brackish water shows much higher salt removal efficiency and lower salt removal rate than that using the IEE and mining water. This results from the lower concentration (i.e., higher ohmic resistance) and salt amount of the influent.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2017.05a
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• pp.162-162
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• 2017

AlCrN 코팅은 높은 경도, 낮은 표면 조도 등의 상온에서의 우수한 기계적 특성 이외에 고온에서 안정한 합금상의 형성으로 인하여 우수한 내열성을 보이는 코팅이며, Si을 첨가하여 나노복합구조를 갖는 AlCrSiN 코팅은 고경도 특성을 나타내는 나노결정립과 고내열성을 나타내는 $Si_3N_4$ 비정질이 동시에 존재함으로써 뛰어난 고온 특성까지 보유하여 공구 코팅으로의 적용 가능성이 크다. 본 연구에서는, 가혹화된 공구사용 환경 대응 하는 더욱 우수한 내마모성 및 내열성을 보이는 코팅막을 개발하기 위해 AlCrN/AlCrSiN 이중층 코팅을 합성하였다. 합성된 코팅의 구조 및 물성을 분석하기 위해 field emission scanning electron microscopy(FE-SEM), nano-indentation, atomic force microscopy(AFM) 및 ball-on-disk wear tester를 사용하였다. 내열성을 확인하기 위하여 코팅을 furnace에 넣어 500, 600, 700, 800, 900도에서 30분 동안 annealing한 후에 nano-indentation을 사용하여 경도를 측정을 하였다. 5:5, 7:3, 9:1의 두께 비율로 AlCrN/AlCrSiN 이중층 코팅을 합성하였으며 모든 코팅의 두께는 $3{\mu}m$로 제어되었다. AlCrN 코팅층의 두께가 증가할수록, 이중층 코팅의 경도 및 내마모성은 점차 향상되었지만 코팅의 밀착력은 감소하였다. 일반적으로 AlCrN 코팅은 상대적으로 높은 잔류응력을 갖고 있으므로, AlCrN 층의 두께비율이 증가함에 따라 코팅내의 잔류응력이 높아져 코팅의 경도는 증가하고 밀착특성은 낮아진 것으로 판단된다. AlCrSiN 상부층 공정시 기판 바이어스 전압을 -50 ~ -200V 로 증가시키면서 이중층 코팅을 합성하였다. XRD 분석 결과, 공정 바이어스 전압이 증가함에 따라 AlCrSiN 상부층은 점차 비정질화 되었고, 코팅의 경도와 표면 특성이 향상되는 것을 확인하였다. 이러한 특성 향상은 높은 바이어스 인가가 이온 충돌효과의 증가를 야기시켰으, 이로 인해 치밀한 코팅층 합성에 의한 결과로 판단된다. AlCrN/AlCrSiN 이중층 코팅을 어닐링 한 후 경도 분석 결과, -150, -200V에서 합성한 코팅은 900도 이상에서 26GPa 이상의 높은 경도를 보인 것으로 보아 우수한 내열성을 갖는 것으로 확인 되었다. 이는 AlCrSiN 상부층의 높은 Si 함량 (11at.%) 으로 인한 충분한 $Si_3N_4$ 비정질상의 형성과, 고바이어스 인가로 인한 AlCrN 결정상과 $Si_3N_4$ 비정질상의 고른 분배가 코팅의 내열성을 향상시키는데 기여를 한 결과로 판단된다.