• 대한금속재료학회지
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• 제47권9호
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• pp.597-603
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• 2009

The hydrogen reduction behavior of ultrasonic ball-milled $WO_3-CuO$ nanopowder, which is highly related with micro-pore structure, was investigated by thermogravimetry(TG) and hygrometry system. EDS and TEM results represented that the ultrasonic ball-milled $WO_3-CuO$ nanopowder consisted of the agglomerates which was confirmed as a homogeneous mixture of $WO_3$ and CuO particles. It was found that the reduction reaction of CuO was retarded by initial micro-pores which are smaller than 40 nm in the ultrasonic ball-milled $WO_3-CuO$ nanopowder. The earlier agglomeration of Cu particles at comparably low temperature decreased the volume of micro-pores in the $WO_3-CuO$ nanopowder which caused the retardation of $WO_3$ reduction reaction. These results clearly explain that the micro-pore structure significantly affected the reduction reaction of $WO_3$ and CuO in the $WO_3-CuO$ nanopowder.

• 공업화학
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• 제9권6호
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• pp.846-851
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• 1998

w/o 에멀젼 내에서 균일용액침전반응을 진행시켜 산화아연 미세 입자를 제조하는 실험적 연구를 수행하였다. 질산아연 수용액에 hexamethylene tetramine (HMTA)을 침전제로 첨가한 침전액은 유화제 Span 80에 의해 kerosine과 안정한 w/o 에멀젼을 형성하였다. 얻어진 w/o 에멀젼을 HMTA 분해온도 이상($85^{\circ}C$)으로 가열하여 w/o 에멀젼 내에서 균일용액 침전반응을 진행시키면 산화아연 입자들이 제조되는 것을 확인하였다. 이렇게 제조된 산화아연 입자들은 이중분산 (bi-modal distribution)을 갖는 영역이 존재하기도 하였으나, 균일용액침전법에 비하여 높은 초기 아연농도와 높은 수율에서도 입자가 작고 입도분포가 비교적 좁은 산화아연 입자들을 얻을 수 있었다.

• 한국수소및신에너지학회논문집
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• 제26권1호
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• pp.28-34
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• 2015

HCCI (Homogeneous Charged Compression Ignition) hydrogen engine has relatively narrower operation range caused by backfire occurrence due to the rapid pressure rising by using higher compression ratio and significant reaction velocity. In this study, to grasp of backfire process and characteristic in the HCCI research hydrogen engine, in-cylinder pressure, intake pressure and backfire limit range are analyzed with compression ratio and intake valve open timing, experimentally. As the result, it is observed that knock is occurred just before backfire occurrence in HCCI hydrogen engine but not spark igntion type, this phenomenon is always the same for the above variables. Also backfire limit range are expanded up to 50% for the more retarding intake valve open timing in this operating conditions.

• 한국세라믹학회지
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• 제26권1호
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• pp.132-138
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• 1989

High purity(99.99%) spherical particles of hydrated Basic Aluminum Salts(BAS) were prepared by a homogeneous precipitation process utilizing the urea decomposition reaction and characterized by XRD, SEM, TG-DTA, IR and PSA methods. Amorphous hydrated BAS was precipitated in the range of pH 4~6. The molar ratio [Al3+]/[SO42-] for the precipitate particles was about 3.7. With increasing the concentration of aluminum sulfate the precipitation of the hydrated BAS occurred slowly and the precipitate particles with a narrow size distribution were fine(1-2${\mu}{\textrm}{m}$ in diameter). At temperatures in the range 400$^{\circ}$to 95$0^{\circ}C$, desulfurization and dehydroxylization resulted in weight loss with 22%. When the precipitate particles were thermally treated, the crystlline ${\gamma}$-Al2O3 was identifited by XRD at 50$0^{\circ}C$ and ${\gamma}$-Al2O3 particles were transformed into $\alpha$-Al2O3 at 100$0^{\circ}C$. A vermicular network was produced by calcining at 125$0^{\circ}C$ for 30min.

• Journal of Forest and Environmental Science
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• 제31권1호
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• pp.1-6
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• 2015

Microwave assisted biodiesel production from crude Pongamia pinnata oil using homogeneous base catalyst (KOH) was unsuccessful because of considerable soap formation. Therefore, a two step process of biodiesel production from high free fatty acid (FFA) oil was investigated. In first step, crude P. pinnata oil was acid catalyzed using $H_2SO_4$ and acid value of oil was reduced to less than 4 mg KOH/g. Effect of sulfuric acid concentration, alcohol-oil molar ratio and microwave irradiation time on acid value of oil was studied. Result suggested that 1.5% $H_2SO_4$ (w/w), 6:1 methanol oil molar ratio and 3 min microwave irradiation time was sufficient to reduce the acid value of oil from 12 and 22 mg KOH/g to 2.9 and 3.9 mg/KOH/g, respectively. Oil obtained after pretreatment was subsequently used for microwave assisted alkali catalyzed transesterification. A higher biodiesel yield (99.0%) was achieved by adopting two step processes. Microwave energy efficiency during alkali catalyzed transesterification was also investigated. The results suggested a significant energy saving because of reduced reaction time under microwave heating.

• 한국응용과학기술학회지
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• 제26권3호
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• pp.288-296
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• 2009

In this study, the silica-based hybrid material with high barrier property was prepared by incorporating ethylene-vinyl alcohol (EVOH) copolymer, which has been utilized as packaging materials due to its superior gas permeation resistance, during sol-gel process. In preparation of this EVOH/$SiO_2$ hybrid coating materials, the (3-glycidoxy-propyl)-trimethoxysilane (GPTMS) as a silane coupling agent was employed to promote interfacial adhesion between organic and inorganic phases. As confirmed from FT-IR analysis, the physical interaction between two phases was improved due to the increased hydrogen bonding, resulting in homogeneous microstructure with dispersion of nano-sized silica particles. However, depending on the range of content of added silane coupling agent (GPTMS), micro-phase separated microstructure in the hybrid could be observed due to insufficient interfacial attraction or possibility of polymerization reaction of epoxide ring in GPTMS. The oxygen barrier property of the mono-layer coated BOPP (biaxially oriented polypropylene) film was examined for the hybrids containing various GPTMS contents. Consequently, it is revealed that GPTMS should be used in an optimum level of content to produce the high barrier EVOH/$SiO_2$ hybrid material with an improved optical transparency and homogeneous phase morphology.

• International Journal of Automotive Technology
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• 제8권1호
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• pp.1-7
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• 2007

The effect of the di-tertiary butyl peroxide (DTBP) additive on the heat release rate and emissions of a homogeneous charge compression ignition (HCCI) engine fueled with high Research Octane Number (RON) fuels were investigated. The experiments were performed using 0%, 1%, 2%, 3%, and 4% (by volume) DTBP-RON90 blends. The RON90 Fuel was obtained by blending 90% iso-octane with 10% n-heptane. The experimental results show that the operation range was remarkably expanded to lower temperature and lower engine load with the DTBP additive in RON90 fuel. The first ignition phase of HCCI combustion was observed at 850 K and ended at 950 K while the hot ignition occurred at 1125 K for all fuels at different engine working conditions. The chemical reaction scale time decreases with the DTBP addition. As a result, the ignition timing advances, the combustion duration shortens, and heat release rates were increased at overall engine loads. Meanwhile, the unburned hydrocarbon (UHC) and CO emissions decrease sharply with the DTBP addition while the NOx emissions maintain at a lower level.

• 분석과학
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• 제12권3호
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• pp.230-234
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• 1999

$Ba^{2+}$ 및 $Ti^{4+}$이 함유된 염산용액에서 dimethyl oxalate(DMO)가 열분해되면 barium titanyl oxalate(BTO)가 균일 생성되었다. 일정량의 hydroxy propyl cellulose(HPC)를 분산제로 사용하였고 120min의 숙성시간에서 생성된 BTO의 전 침전물을 회수하였다. 반응온도, 염화이온의 농도, $[DMO]_0/([Ba^{2+}]_0+[Ti^{4+}]_0)$의 초기 농도비, 그리고 가한 HPC가 BTO입자의 형태, 화학적 회수율, 그리고 그들의 선구물질로부터 형성된 티탄산 바륨의 특성에 영향을 미침을 알았다.

• Nuclear Engineering and Technology
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• 제50권3호
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• pp.389-395
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• 2018

The present work aims to report the consequences of Darcy-Forchheimer medium in flow of Cross fluid model toward a stretched surface. Flow in porous space is categorized by Darcy-Forchheimer medium. Further heat transfer characteristics are examined via thermal radiation and heat generation/absorption. Transformation procedure is used. The arising system of nonlinear ordinary differential equations is solved numerically by means of shooting method. The effects of different flow variables on velocity, temperature, concentration, skin friction, and heat transfer rate are discussed. The obtained outcomes show that velocity was enhanced with the increase in the Weissenberg number but decays with increase in the porosity parameter and Hartman number. Temperature field is boosted by thermal radiation and heat generation; however, it decays with the increase in the Prandtl number.

• 에너지공학
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• 제23권1호
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• pp.58-66
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• 2014

저등급탄인 내몽골 갈탄의 촉매가스화반응을 수행하였다. 가스화반응은 열중량분석기(TGA)에서 반응온도 $600{\sim}900^{\circ}C$ 범위에서 이산화탄소를 반응가스로 하여 실행하였다. 공정설계에 필수적인 반응 인자들을 도출하기 위하여 세가지의 기-고체 반응모델을 사용하였으며 그 모델들이 가스화반응의 거동을 예측하는 능력을 비교하였다. 사용된 모델 중에서 modified volumetric reaction model이 촉매, 비촉매 가스화반응의 거동을 가장 잘 묘사하였다. 이론적 모델인 homogeneous model과 shrinking-core model은 비촉매반응과 $FeSO_4$를 촉매로 한 반응을 비교적 잘 표현하였다. 알칼리금속 촉매를 사용할 경우, 촉매의 활성은 $600^{\circ}C$ 낮은 온도에서 가장 크게 나타났으며 온도가 $700^{\circ}C$로 증가하면 촉매활성이 약 50% 감소하는 것이 관찰되었다. 온도가 더 증가하여 $800^{\circ}C$ 이상에서는 촉매활성은 일정해졌다. 본 연구에서 촉매의 활성 순서는 다음과 같이 얻어졌다: $K_2CO_3$ > $Na_2CO_3$ > $K_2SO_4$ > $FeSO_4$.