• International Journal of Precision Engineering and Manufacturing
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• 제9권2호
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• pp.39-43
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• 2008

Atmospheric pressure plasma polishing (APPP) is a noncontact precision machining technology that uses low temperature plasma chemical reactions to perform atom-scale material removal. APPP is a complicated process, which is affected by many factors. Through a preliminary theoretical analysis and simulation, we confirmed that some of the key factors are the radio frequency (RF) power, the working distance, and the gas ratio. We studied the influence of the RF power and gas ratio on the removal rate using atomic emission spectroscopy, and determined the removal profiles in actual operation using a commercial form talysurf. The experimental results agreed closely with the theoretical simulations and confirmed the effect of the working distance. Finally, we determined the element compositions of the machined surfaces under different gas ratios using X-ray photoelectron spectroscopy to study the influence of the gas ratio in more detail. We achieved a surface roughness of Ra 0.6 nm on silicon wafers with a peak removal rate of approximately 32 $mm^{3}$/min.

• 한국전기전자재료학회논문지
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• 제18권10호
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• pp.909-916
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• 2005

The structural and electrical property of RF magnetron sputtered ZnO thin film have been studied as a function of RF power, substrate temperature, oxygen/argon gas ratio and film thickness at constant sputtering power, sputtering working pressure and target-substrate distance. To analyze a crystallo-graphic properties of the films, $\theta$/2$\theta$ mode X-ray diffraction, SEM, and AFM analyses. C-axis preferred orientation, resistivity and surface roughness highly depended on oxygen/argon gas ratio. The resistivity of ZnO thin film(6000 ${\AA}$) rapidly increased with increasing oxygen ratio and the resistivity value of $9 {\ast} 10^7 {\Omega}cm$ was obtained at a working pressure of 10 mTorr with the same oxygen/argon gas ratio. The surface roughness was also improved with increasing oxygen ratio and the ZnO films deposited with the same oxygen/argon gas ratio showed the excellent roughness value of 28.7 ${\AA}$. With increase of the substrate temperature, The C-axis preferred orientation of ZnO thin film increases and the resistivity decreases due to deviation from the stoichiometric ZnO due to oxygen deficiency.

• 한국유체기계학회 논문집
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• 제14권2호
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• pp.41-46
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• 2011

This study investigated the changes in performance and operating characteristics of an F-class gas turbine according to the change of working fluid from air to carbon dioxide. The revised gas turbine is the topping cycle of the semi-closed oxy-fuel combustion combined cycle. With the same turbine inlet temperature, the $CO_2$ gas turbine is expected to produce about 85% more power. The main contributor is the greater compressor mass flow and the added oxygen flow for the combustion. Compressor pressure ratio increases about 50%. However, the gas turbine efficiency reduces about 10 %. Modulation of inlet guide vane to reduce the compressor inlet mass flow, the major purpose of which is to reduce the compressor inlet Mach number, was also performed.

• 한국전기전자재료학회논문지
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• 제17권7호
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• pp.724-728
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• 2004

This paper describes on RIE(Reactive Ion Etching) characteristics of 3C-SiC(Silicon Carbide) grown on Si(100) wafers. In this work, CHF$_3$ gas was used to form the polymer as a function of a side-wall for excellent anisotropy etching during the RIE process. The ranges of the etch rate were obtained from 60 $\AA$/min to 980 $\AA$/min according to the conditions such as working gas pressure, RF power, distance between electrodes and the $O_2$ addition ratio in working gas pressure. Under the condition such as 100 mTorr of working gas pressure, 200 W of RF power and 30 mm of the distance between electrodes, mesa structures with about 40 of the etch angle were formed, and the vertical structures could be improved with 50 % of $O_2$ addition ratio in reactive gas during the RIE process. As a result of the investigation, we know that it is possible to apply the RIE process of 3C-SiC using CHF$_3$ for the development of electronic parts and MEMS applications in harsh environments.

• 공업화학
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• 제10권3호
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• pp.400-406
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• 1999

고효율 가스흡수식 냉방기를 위한 신 작동매체로 기존의 $LiBr-H_2O$ 용액에 $LiNO_3$, LiCl, LiI 성분을 첨가하여 4성분 용액을 제조하였다. 본 연구를 통하여 제조된 4성분계의 작동매체에 대한 용해도와 증기압을 측정하여 기존의 $LiBr-H_2O$계와 비교 분석하였으며, 이들에 대한 최적혼합 몰비를 각각 구하였다. 용해도 측면에서 $LiBr-LiNO_3-LiCl$계는 5:1:1~2, $LiBr-LiNO_3-LiCl$계는 5:1:1, LiBr-LiI-LiCl계의 경우 5:1:0.5~1로 나타났다. 한편 $LiBr-LiNO_3-LiCl-H_2O$계를 제외하고 모두 증기압이 $LiBr-H_2O$계에 비해 높게 나타났다. $LiBr-LiNO_3-LiCl-H_2O$계를 이용한 흡수성능 실험시 $LiBr-H_2O$계 보다 우수한 특성을 지녔다.

• Journal of Ceramic Processing Research
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• 제13권spc2호
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• pp.407-410
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• 2012

The properties of Al-doped ZnO (AZO) films were investigated as a function of H2/(Ar + H2) gas ratio using an AZO (2 wt% Al2O3) ceramic target in a radio frequency (RF) magnetron sputtering system. The deposition process was done at 200 ℃ and in 2 × 10-2Torr working pressure and with various ratios of H2/(Ar + H2) gas. During the AZO film deposition process, partial H2 gas affected the AZO film characteristics. The electron resistivity (~ 9.21 × 10-4 Ωcm) was lowest and mobility (~17.8 ㎠/Vs) was highest in AZO films when the H2/(Ar + H2) gas ratio was 2.5%. When the H2/(Ar + H2) gas ratio was increased above 2.5%, the electron resistivity increased and mobility decreased with increasing H2/(Ar + H2) gas ratio in AZO films. The carrier concentration increased with increasing H2/(Ar + H2) gas ratio from 0% to 7.5%. This phenomenon was explained by reaction of hydrogen and oxygen and additional formation of oxygen vacancy. The average optical transmission in the visible light wavelength region over 90% and an orientation of the deposition was [002] orientation for AZO films grown with all H2/(Ar + H2) gas ratios.

• 한국환경보건학회지
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• 제21권4호
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• pp.24-31
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• 1995

Gas sensing element, $\alpha-Fe_2O_3$ was synthesized by dehydration, reduction, and oxidation of $\alpha-FeOOH$, which was synthesized with $FeSO_4\cdot 7H_2O$ and NaOH. They were produced as a bulk-type, a thick film-type. Then, their responses and mechanisms of response to the gas of carbon monoxide were studied. The qualities of gas sefising elements are decided by the structure and the relative surface area. In the process of $\alpha-FeOOH$ synthesis, the effects of reaction conditions as the equivalent ratio, on the structure and the relative surface area of gas sensing element were observed. The changes of the structure were measured with XRD, SEM,TG-DTA and BET. The resistance changes of the synthesized gas sensor in the air were measured. The response ratio were also measured for the changes of working temperature and gas concentration. As a result of analysis with XRD, it was confirmed that the the best conditions for the synthesis of $\alpha-FeOOH$ were equivalent ratio 0.65. The thick film-type element of $\gamma-Fe_2O_3$ responded more quickly than the bulk-type did. The structure and the relative surface area of the $\rho-FeOOH$ were confirmed as the important factors deciding gas response charcteristics.

• 전기학회논문지
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• 제56권9호
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• pp.1619-1625
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• 2007

The gas mixture ratio of PDP discharges plays a very important role in the discharge characteristics of a plasma display panel. The increase of Xe contents results in the increases of luminance and luminous efficiency while it also results in the increase of the breakdown voltage. The addition of He gas increases the brightness and the luminous efficiency. Especially, the luminance and the luminous efficiency have a maximum value when the partial pressure of He is about 10% of the total pressure for a standard plasma display panel with Xe fraction of $10\sim30%$.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 1999년도 유체기계 연구개발 발표회 논문집
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• pp.109-113
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• 1999

Thermal mass flow meter (TMF) is used measuring the small mass flow rate of gases. Generally, flow rate measuring accuracy of TMF is $\pm2{\%}$ of full scale. TMF is manufactured for specified working pressure and specified working gas by customer. If it were applied for different working pressure and gases, flow rate measurement accuracy decreased dramatically. In this study, a TMF tested with three different gases and pressure range of 0.2 MPa to 1.0 MPa. Effect of specific heat cause to increase flow measurement error as much as ratio of specific heat compare with reference gas. Pressure change cause to increase flowrate measurement deviation about $-0.2{\%}$ as the working pressure decreased 0.1 MPa.

• 한국안전학회지
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• 제11권2호
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• pp.67-78
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• 1996

Gas sensing element, $\gamma-Fe_2O_3$was synthesized by dehydration, reduction, and oxidation of $$${\gamma}$-FeOOH, which was synthesized with $FeSO_4\;{\cdot}\;7H_2O$ and NaOH. They were produced as a bulk-type, a thick film-type. Then, their responses and mechanisms of response to the gas of liquefied-petroleum were studied. The qualities of gas sensing elements are decided by the structure and the relative surface area. In the process of $\alpha-FeOOH $synthesis, the effects of reaction conditions as the equivalent ratio, on the structure and the relative surface area of gas sensing element were observed. The changes of the structure were measured with XRD, SEM, TG-DTA and BET. The resistance changes of the synthesized gas sensor in the air were measured. The response ratio were also measured for the changes of working temperature and gas concentration. As a result of analysis with XRD, it was confirmed that the the best conditions for the synthesis of $\alpha -FeOOH$ were equivalent ratio 0.65. The thick film-type element of $\gamma-Fe_2O_3$responded more quickly than the bulk-type did. The structure and the relative surface area of the $\alpha-FeOOH $were confirmed as the important factors deciding gas response charcteristics.