• 한국산학기술학회논문지
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• 제10권11호
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• pp.3074-3079
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• 2009

지속적인 경제 발전과 인구증가로 인하여 에너지 소비가 급증하게 되면서 에너지의 효율적인 사용이 필요하다. 특히 에너지 손실이 많은 건물의 창호에 단열성능이 좋은 고효율 진공유리 사용이 절실한데 아직 가격 및 성능등의 문제로 보급화가 이루어지지 않고 있다. 따라서, 본 연구에서는 저가의 진공유리 개발을 위한 유리 용접용 토치를 설계 및 제작하였다. 연료는 고밀도 열원인 수소-산소 혼합가스를 사용하였고 주로 토치 형상, 노즐 직경, 노즐 배치 등의 최적화를 수행하였다. 끝으로 개발된 토치를 이용하여 두 장의 유리용접을 성공적으로 수행함으로써 저가의 진공유리 개발 가능성을 확인하였다.

• Journal of Magnetics
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• 제15권4호
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• pp.155-158
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• 2010

The HDDR (hydrogenation, disproportionation, desorption, and recombination) process can be used as an effective way of converting a no coercivity Nd-Fe-B ingot material, with a coarse $Nd_2Fe_{14}B$ grain structure, to a highly coercive one with a fine grain structure. Careful control of the HDDR process can lead to an anisotropic powder with good $Nd_2Fe_{14}B$ grain texture; the most critical step for inducing texture is disproportionation. The critical conditions (hydrogen pressure and temperature) for the disproportionation reaction of fully hydrogenated $Nd_{12.5}Fe_{81.1-(x+y)}B_{6.4}Ga_xNb_y$ (x = 0 or 0.3, y = 0 or 0.2) alloys, in different atmospheres of pure hydrogen and a mixed gas of hydrogen and argon, was investigated with TPA (thermopiezic analyser). From this, the hydrogen pressure-temperature diagram showing the critical conditions was established. The critical disproportionation temperature of the fully hydrogenated $Nd_{12.5}Fe_{81.1-(x+y)}B_{6.4}Ga_xNb_y$ alloys was slightly increased as the hydrogen pressure decreased in both pure hydrogen and mixed gas. The critical disproportionation temperature of the hydrogenated alloys was higher in the mixed gas than in pure hydrogen. Addition of Ga and Nb increased the critical disproportionation temperature of the fully hydrogenated Nd-Fe-B alloys.

• 한국표면공학회지
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• 제49권4호
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• pp.339-343
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• 2016

ASTM T23 steel with a composition of Fe-2.25%Cr-1.6%W corroded at 600 and $700^{\circ}C$ for 5-70 h in $N_2$/(0.5, 2.5)%$H_2S$-mixed gas at 1 atm. It corroded rapidly, forming the outer FeS scale and the inner (FeS, $FeCr_2O_4$)-mixed scale. The ensuing outward diffusion of $Fe^{2+}$ ions during corrosion led to the protrusion of FeS platelets over the outer FeS scale. The formation of FeS at the surface facilitated the oxidation of Cr to $FeCr_2O_4$ in the inner scale. Since the nonprotective FeS scale existed over the whole scale, T23 steel displayed poor corrosion resistance in the $H_2S$-containing atmosphere.

• 대한금속재료학회지
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• 제50권3호
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• pp.218-223
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• 2012

Fe-(8.5, 18.5, 28.3, 36.9) wt% Cr alloys were corroded between 600 and $800^{\circ}C$ for up to 70 h in a 1 atm gas mixture that consisted of 0.0242 atm of $H_2S$, 0.031 atm of water vapor, and 0.9448 atm of nitrogen gas. Their corrosion resistance increased with an increment in the Cr content. The Fe-8.5%Cr alloy corroded fast, forming thick, fragile, nonadherent scales that consisted primarily of an outer FeS layer and an inner (Fe, Cr, O, S)-mixed layer. The outer FeS layer grew into the air by the outward diffusion of $Fe^{2+}$ ions, whereas the inner mixed layer grew by the inward diffusion of oxygen and sulfur ions. At the interface of the outer and inner scales, voids developed and cracking occurred. The Fe-(18.5, 28.3, 36.9)% Cr alloys displayed much better corrosion resistance than the Fe-8.5Cr alloy, because thin $Cr_2O_3$ or $Cr_2S_3$ scales formed.

• 대한기계학회논문집
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• 제9권6호
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• pp.743-749
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• 1985

본 연구에서는 Gas Chromatograph를 사용하여 1,500㏄급 국산 소형 승용차 엔 진의 배기가스 성분을 분석하였다. 그리고 이를 통하여 배개가스 성분 분석에 Gas Chromatograph를 사용할 경우 아래와 같은 점에 유의한다면 배기가스 성분을 비교적 정확하게 측정할 수 있다는 것을 확인하였다.

• Asian-Australasian Journal of Animal Sciences
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• 제16권8호
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• pp.1151-1157
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• 2003

The surfactant Tween 80 was evaluated for its ability to influence cumulative gas production, cellulose digestion, and enzyme activities by mixed ruminal microorganisms grown on barley grain or Orchardgrass hay. The addition of Tween 80 at a level of 0.10% significantly (p<0.05) decreased the cumulative gas production rate from both barley grain or Orchardgrass hay substrates. However, 0.05% Tween 80 did not affect gas production rates compared to the control treatment. The addition of 0.05% Tween 80 to cultures growing on barley grain resulted in a significant increase in cellulase (90.01%), xylanase (90.73%) and amylase (487.25%) activities after 30 h incubation. Cultures utilizing Orchardgrass hay had a significant increase in cellulase (124.43%), xylanase (108.86%) and amylase (271.22%) activities after 72 h incubation. These increases in activities were also observed with cultures supplemented with 0.10% Tween 80 throughout all the incubation times tested. These results indicated that the addition of 0.05% Tween 80 could greatly stimulate the release of some of key enzymes without decreasing cell growth rate in contrast to trends reported with aerobic microorganism. Our data indicates potential uses of the surfactant Tween 80 as a feed additive for ruminant animals.

• 한국농공학회논문집
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• 제57권1호
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• pp.79-87
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• 2015

A thermochemical equilibrium model was constructed for predicting composition of synthesis gas in biomass gasification. The model included estimation of equilibrium constants using Gibbs free energy. After constructing the model, the results were compared with the experimental values and predictions from a previous model. Gas compositions were reasonably well agreed with them and showed effects of operational and fuel condition. When the reaction temperature increased, the lower heating values decreased due to the decrease in CH4 concentrations. The methane concentrations were lower than those observed in experimental results. The model was used to predict the gas composition and heating values for the cases of mixed fuel of charcoal and un-dry woodchips. Although downdraft gasifiers require fuels less than 15% of moisture contents, the model results indicated that the mixed fuel with charcoal and woodchips which had over 25% of moisture contents could be used in the downdraft gasifiers. It might be explained by increase in energy density resulting from mixing charcoal. The results imply that the efforts and costs for drying biomass fuels could be reduced by mixing charcoal or fuels with higher calorific values.

• 한국표면공학회지
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• 제29권2호
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• pp.93-99
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• 1996

In this work BN thin films were deposited on Si substrate by R. F. sputtering method at $200^{\circ}C$ and in Ar + $N_2$ mixed gas atmosphere. In order to investigate the effect of ion bombardment on substrate for c-BN bonding, substrate bias voltage was applied. The optimum substrate bias voltage for c-BN bonding was determined by FTIR analysis on specimens which were deposited with various bias voltages. Then BN thin film was deposited with this optimum condition and its phase, morphology, chemical composition, and refractive index were compared with those of BN film which was deposited without bias voltage. FTIR results showed that BN films deposited with substrate bias voltage were composed of mixed phases of c-BN and h-BN, while those deposited without bias voltage were h-BN only. When pure Ar gas was used for sputtering gas, BN films were delaminated easily from substrate in air, while when 10% $N_2$ gas was added to the sputtering gas, although c-BN specific infrared peak was reduced, delamination did not occur. GXRD and TEM results showed that BN films were amorphous phases regardless of substrate bias voltage, and AES results showed that the chemical compositions of B/N were about 1.7~1.8. The refractive index of BN film deposited with bias voltage was higher than that without bias voltage. The reason is believed to be the existence of c-BN bonding in BN film and the higher density of film that deposited with the substrate bias voltage.

• 한국레이저가공학회지
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• 제7권2호
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• pp.19-26
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• 2004

The effect of shield gas on the weldability, mechanical properties and formability of CO2 laser weld joint in 600MPa grade high strength steel was investigated. Bead on plate welds were made under various welding speed and shield gas. Tensile test was carried out under the load of perpendicular and parallel direction to the weld line, Formability of the joint was evaluated by Erichsen test. As the welding speed increases, the porosity fraction decreases. The porosity fraction in the joint used Ar-$50\%He$ mixed gas as a shield gas was lower than that of the joint used Ar gas. Hardness at the weld metal of full penetrated joint was nearly equal to that of water quenched raw metal. In a tensile test under a perpendicular load to the weld axis, strength and elongation of joint produced by optimum condition were nearly equal to those of base metal. However, the strength of joint in a tensile test under a parallel load to weld axis was higher than that of raw metal, but the elongation of joint was lower than that of raw metal. Elongation and formability were further increased by the method of using Ar+He mixed gas as a shield gas as compared with Ar gas. Formabilities of joints were recorded ranging from $58\%\;to\;70\%$ of that of base metal with different shield gases.

• 한국가스학회지
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• 제19권2호
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• pp.37-44
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• 2015

본 연구에서는 CBM의 1차 생산뿐 아니라 $CO_2$나 $N_2$ 주입을 통한 ECBM, 혹은 지중저장을 목적으로 석탄층에 $CO_2$를 주입할 때 발생할 수 있는 암체의 부피변화 영향을 고려하여 기존의 Langmuir 흡착 관계식을 개선하였다. 본 모델의 검증을 위해 $CO_2$나 $CH_4$, $N_2$의 단일성분 흡착실험 데이터에 기존 Langmuir 모델값과 본 모델의 결과값을 비교하였다. 그 결과, 기존 모델에서는 흡착용량이 큰 석탄일수록, 흡착친화도가 큰 가스일수록 실험값과 모델값 사이의 오차가 커지는 경향이 나타났지만 본 모델에서는 모든 조건에서 실험결과를 잘 묘사하였고 본 모델을 통해 예측한 부피변형률 역시 실험값과 유사함을 확인하였다. 이렇게 개선된 단일성분 흡착모델을 혼합가스의 흡착모델인 IAS 모델에 적용하여 부피변화가 고려된 IAS모델로 개선하였다. 그 결과 혼합가스에 대한 흡착거동 역시 기존 모델에 비해 정확도를 높였고 이는 Hall 등(1994)이 수행한 혼합가스의 흡착실험결과와의 매칭을 통해 확인하였다.