• Journal of the Computational Structural Engineering Institute of Korea
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• v.32 no.2
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• pp.103-108
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• 2019

Non-equilibrium molecular dynamics simulation on the thermal boundary resistance(TBR) of an aluminum(Al)/silicon(Si) interface was performed in the present study. The constant heat flux across the Si/Al interface was simulated by adding the kinetic energy in hot Si region and removing the same amount of the energy from the cold Al region. The TBR estimated from the sharp temperature drop at the interface was independent of heat flux and equal to $5.13{\pm}0.17K{\cdot}m^2/GW$ at 300K. The simulation result was experimentally confirmed by the time-domain thermoreflectance technique. A 90nm thick Al film was deposited on a Si(100) wafer using an e-beam evaporator and the TBR on the film/substrate interface was measured using the time-domain thermoreflectance technique based on a femtosecond laser system. A numerical solution of the transient heat conduction equation was obtained using the finite difference method to estimate the TBR value. Experimental results were compared to the prediction and discussions on the nanoscale thermal transport phenomena were made.

• Journal of the Korean Society for Marine Environment & Energy
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• v.11 no.4
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• pp.181-190
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• 2008

To response climate change and Kyoto protocol and to reduce greenhouse gas emissions, marine geological storage of $CO_2$ is regarded as one of the most promising option. Marine geological storage of $CO_2$ is to capture $CO_2$ from major point sources(eg. power plant), to transport to the storage sites and to store $CO_2$ into the marine geological structure such as deep sea saline aquifer. To design a reliable $CO_2$ marine geological storage system, it is necessary to perform numerical process simulation using thermodynamic equation of state. The purpose of this paper is to compare and analyse the relevant equations of state including ideal, BWRS, PR, PRBM and SRK equation of state. To evaluate the predictive accuracy of the equation of the state, we compared numerical calculation results with reference experimental data. Ideal and SRK equation of state did not predict the density behavior above $29.85^{\circ}C$, 60 bar. Especially, they showed maximum 100% error in supercritical state. BWRS equation of state did not predict the density behavior between $60{\sim}80\;bar$ and near critical temperature. On the other hand, PR and PRBM equation of state showed good predictive capability in supercritical state. Since the thermodynamic conditions of $CO_2$ reservoir sites correspond to supercritical state(above $31.1^{\circ}C$ and 73.9 bar), we conclude that it is recommended to use PR and PRBM equation of state in designing of $CO_2$ marine geological storage process.

• Clean Technology
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• v.28 no.1
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• pp.46-53
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• 2022

The agglomeration characteristics of coal and silica sand were investigated under various conditions using mixed samples consisting of coal, silica sand, and potassium hydroxide, which is an agglomeration accelerator. The samples were prepared by either physically mixing or using aqueous solutions. The experiments using the physically mixed powder samples were performed with a two hour reaction time. The results showed that the number of aggregates generated increased as the reaction temperature and the total potassium content increased. The experiments using aqueous solutions were performed at 880 ℃, which is the operating temperature of a fluidized bed boiler, and at 980 ℃, which assumes a local hot spot. The amount of agglomeration generated as the reaction time increased and the total potassium content increased was identified. In the experiment performed at 880 ℃, the amount of aggregate generated clearly increased with the reaction time, and in the experiment performed at 980 ℃, assuming a local hot spot, a large amount of aggregate was generated in a relatively short time. The aggregates became harder as the potassium content increased. When the total potassium content was less than 1.37 wt.%, the aggregates were weak at both temperatures and collapsed even with a slight impact. Additionally, the surface characteristics of the silica sand and ash aggregates were observed by SEM-EDS analysis. The analysis revealed a large amount of potassium at the bonding sites. This result indicates that there is a high possibility of aggregation in the form of a eutectic compound when the alkali component is increased.

• Korean Chemical Engineering Research
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• v.52 no.5
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• pp.688-693
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• 2014

For investigating NO reduction activity of an catalytic filter, the catalytic performance was measured under the presence of $SO_2$ and $H_2O$, respectively or simultaneously in the simulation gas composed of NO, $NH_3$, and air. The catalytic filter was prepared by coating $V_2O_5-WO_3/TiO_2$ catalyst on the pore surface of SiC filter element of which the superior performance for the particulate removal was well known. At the temperature below $260^{\circ}C$, the catalytic activities were enormously decreased under the presence of $SO_2$ and $H_2O$, respectively or simultaneously, compared with those under the cases of the absence of $SO_2$ and $H_2O$. However, the presence of $SO_2$ promoted the performance of the catalytic filter above $320^{\circ}C$ with showing the NO conversion better than 99.8% for the NO inlet concentration of 500 ppm and at the face velocity of 2 cm/s. In particular, the presence of water showed high NO conversion higher than 99% up to high temperature of $380^{\circ}C$. This effect of water was explained by the reason that it retarded the ammonia oxidation which is the main step into the formation of $N_2O$. The initial NO reduction activity of the catalytic filter maintained for the duration of 100 hours in the presence of $SO_2$ and $H_2O$. Therefore, it was concluded that the catalytic filter was promisingly useful for the industrial NOx reduction catalyst in order to treat the particulate and NO simultaneously.

• The Journal of the Petrological Society of Korea
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• v.6 no.2
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• pp.123-132
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• 1997

In the system $MgO-SiO_2-H_2O$, Talc[$Mg_3Si_4O_{10}(OH)_2$] has been synthesized hydrothermally at 200 MPa, $600^{\circ}C$ from the oxide mixture of the bulk composition of talc. The oxide mixture of the bulk composition of anthophyllite$[Mg_7Si_8O_{22}(OH)2]$ converted to talc, enstatite $(MgSiO_3)$, quartz at 200 MPa, $750^{\circ}C$ with excess of $H_2O$. In low to medium pressure metramorphism, enstatite-talc assemblage is metastable relative to anthophyllite with the reaction talc + 4 enstatite=anthophyllite (Greenwood, 1963). The high temperature stability of talc is bounded with the dehydration reaction to anthophyllite rather than that to enstatite(Greenwood, 1963; Chernosky et al., 1985). Therefore our experiment result assemblage, enstatite-talc-quatz at 200 MPa, $750^{\circ}C$ from oxide mixture of bulk compostion of anthophyllite is metastable assemblage. The hydrothermal experiment performed at 41 to 243 MPa, 680 to $760^{\circ}C$ with the starting material composed of synthetic talc, enstatite and quartz. Talc or enstatite grows during the runs and no extra phases including anthophyllite nucleated. Based on the increase or decrease of the each phase from run products, one of the possible reactions is talc=3 enstatite+quartz+H_2O$. The reversal bracket of the reaction is 699 to $700^{\circ}C$ at 100 MPa. Talc is stable up to $740^{\circ}C$ at 200 MPa and enstatite grow at $680^{\circ}C$, 40 MPa and at $760^{\circ}C$, 250 MPa. Though the high temperature limit of talc around 200 MPa is bounded thermodynamically by the reaction, 7 talc=3 anthophyllite+4 quartz+4 H_2O$, talc persisted throughout the previous reaction up to the reaction, talc=3 enstatite+quartz+$H_2O$.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.425-426
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• 2013

IIIN계 물질 기반의 광 반도체는 직접 천이형 넓은 밴드갭 구조를 갖고 있기 때문에 적외선부터 가시광선 및 자외선까지를 포함한 폭 넓은 발광파장 조절이 가능하여 조명 및 디스플레이 관련 차세대 광원으로 많은 관심을 받고 있다. 일반적인 청색 및 녹색 발광영역의 활성층으로는 InGaN/GaN 다중양자우물구조를 사용하고 있으나, 장파장의 녹색 발광을 얻기 위해서는 인듐의 함유량이 증가하여야 한다. 하지만, 인듐의 함유량이 증가함에 따라서 InGaN/GaN 다중양자우물 구조내에서 인듐의 편석현상의 발생이 용이하게 되어 계면 특성을 저하할 뿐 아니라, 비발광 센터를 증가하여 발광 효율을 급격히 감소시키는 원인이 되고 있다. 또한, InGaN과 GaN의 큰 성장온도의 차이에 따라 800도 부근의 저온 영역에서 성장된 InGaN층이 1,000도 이상의 고온 영역에서 GaN층이 성장시 InGaN층의 열화 현상이 급격히 발생되고 있다. 이를 억제하기 위해서 금속유기화학증착법의 성장 변수 최적화, 응력제어, 도핑 등의 편석 억제기술 및 보호층이 사용되고 있다. 본 연구에서는 인듐함유량이 증가된 녹색 InGaN/GaN 다중양자우물구조에서 InGaN 우물층 상하부에 도입된 GaN 보호층에 따라 발생되는 양자우물구조의 광학 및 결정학적 특성 분석을 통해 GaN 보호층의 역할을 분석하고자 한다. 본 연구에서는 금속유기화학증착장치를 이용하여 사파이어 기판위에 GaN 템플릿을 성장하고, n-형 GaN, InGaN/GaN 다중양자우물구조 및 p-형 층을 성장하였다. 앞선 언급하였듯이, InGaN/GaN 다중양자우물구조내에 GaN 보호층의 역할을 규명하기 위하여 샘플 A의 경우는 보호층이 전혀 없는 구조이고, 샘플 B의 경우는 InGaN 우물층의 상단부에만, 샘플 C의 경우에는 우물층 상부 및 하단부 모두에 약 2.0 nm 두께의 GaN 보호층을 형성하였다. 이 보호층의 유무에 따른 다중양자우물구조의 계면 특성을 확인하기 위한 X-선 회절을 이용하였고, 광학적 특성을 확인하고 상온 포토루미네선스법을 이용하여 녹색 발광 파장의 변화 및 발광세기를 관찰하였다. 우선적으로, 상온 포토루미네선스법을 이용하여 각 샘플의 발광특성을 확인한 바 상하부 모두에 GaN 보호층이 존재하는 샘플 C의 경우 약 510 nm 부근에서 발광이 관찰되었지만, 상단부에 GaN 보호층이 존재하는 샘플 B는 약 495 nm영역에 발광이 확인되었다. 특히, 전혀 보호층이 존재하지 않는 샘플 A의 경우 약 440 nm에서 발광하는 현상을 관찰하였다. 이는 우물층 상단부 및 하단부에 존재하는 GaN 보호층이 In의 확산을 억제하는 것으로 판단된다. 또한, 발광파장 및 세기를 확인한 바, 보호층의 존재하지 않을수록 단파장화가 발생함에도 불구하고 발광세기는 급격히 약해지는 것으로 보아 계면특성이 저하되어 비발광센터가 증가되는 것으로 판단된다. 이를 구조적으로 확인하기 위하여 X-선 회절법을 통한 ${\omega}$/$2{\Theta}$ 스캔의 결과는 In의 0차 피크가 GaN 보호층이 없을 경우 GaN의 피크 방향으로 이동하는 것으로 보아 GaN 보호층은 우물층 성장 후 GaN 장벽층을 성장하기 위해 온도를 증가시키는 과정에서 In의 확산되는 것으로 판단된다. 또한, 하부 GaN 보호층의 경우 GaN 장벽층 성장 후 온도를 감소시키는 과정에서 성장되므로, 우물층으로부터 In의 탈착현상이 아닌 장벽층과의 상호 확산으로 판단된다. 또한, 계면특성을 확인하기 위해 InGaN의 X-선 위성 피크를 확인한 바 샘플 A의 경우 매우 넓고 약한 피크가 관찰된 반면, 보호층이 존재하는 샘플 B와 C의 경우 강하고 얇은 피크가 확인되었다. 이는 GaN 보호층의 도입으로 인해 계면특성이 향상되는 것으로 판단된다. 따라서, 우리는 InGaN/GaN 다중양자우물구조에서 GaN 보호층은 상부의 열화 억제 뿐아니라, 하부의 장벽층 및 우물층 사이의 상호확산을 억제하는 GaN 보호층의 도입을 통하여 우수한 계면 특성 및 비발광센터의 억제를 얻을 수 있을 것으로 생각되며, 이는 향후 GaN계 발광다이오드의 전계 발광특성을 증가하여 우수한 발광소자를 개발할 수 있을 것으로 기대된다.

• Journal of the Mineralogical Society of Korea
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• v.6 no.1
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• pp.1-16
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• 1993

The chemical and optical absorption spectroscopic characters of pink and colorless tourmalines from San Diego mine in California, U.S.A., blue/green tourmalines from anonymous mine, Brazil, and brownis black tourmalines from Uncheon and Haksan mines in Korea have been studied using X-ray diffractometer, electron microprobe, optical absorption spectroscopy, and heat treatment. Least-squares refinements give unit cell diminsions : a = 15.96-16.01 ${\AA}$, c = 7.15-7.16 ${\AA}$ for the brownish black tourmalines, a = 15.82 - 15.87 ${\AA}$, c = 7.09 - 7.10 ${\AA}$ for pink tourmalines, and a = 15.88 - 15.94 ${\AA}$, c = 7.12 - 7.15 ${\AA}$ for blue green tourmalines. The colors of tourmalines are responsible for the transition elements. The pink color is attributed to the $Mn^{3+}$ ions, the blue-green to $Fe^{2+}$ and $Mn^{2+}$, bluish green to $Cu^{2+}$, and the brownish black to $Fe^{2+}$, $Fe^{2+}$ - $Fe^{3+}$, and $Fe^{2+}$ - $Ti^{4+}$. The $Mn^{3+}$ ions of pink color tourmalines are stabilized in the Y sites compressed along the O(1)H-O(3)H axis by Jahn-Teller distortion. Heating removes the pink or red component from tourmalines, producing the colorless stones from the pink and red ones. The bluish green samples change into the greenish blue ones and a certain yellowish green samples change into the light green ones by heat treatment. In the elbaite-schorl series, the concentration of Fe and Mn are variable depending on the color zones. The green zone is characterrized by the high content of Fe and Mn are variable depending on the color zones. The green zone is characterized by the high content of Fe, whereas the pink zone by the high content of Mn. Mn increases in deep yellow zone compared with yellow or colorless zones.

• Korean Chemical Engineering Research
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• v.51 no.3
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• pp.313-318
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• 2013

In order to investigate the effect of $V_2O_5$ loading of $V_2O_5-WO_3/TiO_2$ catalyst on the NO reduction and the formation of $N_2O$, the experimental study was carried out in a differential reactor using the powder catalyst. The NO reduction and the ammonia oxidation were, respectively, investigated over the catalysts compose of $V_2O_5$ content (1~8 wt%) based on the fixed composition of $WO_3$ (9 wt%) on $TiO_2$ powder. $V_2O_5-WO_3/TiO_2$ catalysts had the NO reduction activity even under the temperature of $200^{\circ}C$. However, the lowest temperature for NO reduction activity more than 99.9% to treat NO concentration of 700 ppm appeared at 340 with very limited temperature window in the case of 1 wt% $V_2O_5$ catalyst. And the temperature shifted to lower one as well as the temperature window was widen as the $V_2O_5$ content of the catalyst increased, and finally reached at the activation temperature ranged $220{\sim}340^{\circ}C$ in the case of 6 wt% $V_2O_5$ catalyst. The catalyst of 8 wt% $V_2O_5$ content presented lower activity than that of 8 wt% $V_2O_5$ content over the full temperature range. NO reduction activity decreased as the $V_2O_5$ content of the catalyst increased above $340^{\circ}C$. The active site for NO reduction over $V_2O_5-WO_3/TiO_2$ catalysts was mainly related with $V_2O_5$ particles sustained as the bare surface with relevant size which should be not so large to stimulate $N_2O$ formation at high temperature over $320^{\circ}C$ according to the ammonia oxidation. Currently, $V_2O_5-WO_3/TiO_2$ catalysts were operated in the temperature ranged $350{\sim}450^{\circ}C$ to treat NOx in the effluent gas of industrial plants. However, in order to save the energy and to reduce the secondary pollutant $N_2O$ in the high temperature process, the using of $V_2O_5-WO_3/TiO_2$ catalyst of content $V_2O_5$ was recommended as the low temperature catalyst which was suitable for low temperature operation ranged $250{\sim}320^{\circ}C$.

• Korean Chemical Engineering Research
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• v.49 no.5
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• pp.633-638
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• 2011

Mn substituted La, Sr or Ba-hexaaluminate were prepared by $(NH_4)_2CO_3$ co-precipitate method and calcined at $1,200^{\circ}C$ for 5 h. Catalysts were characterized by X-ray diffraction and $N_2$ physisorption and scanning electron microscope (SEM). Compared to $SrMnAl_{11}O_{19}$ and $BaMnAl_{11}O_{19}$, $LaMnAl_{11}O_{19}$ in which La located at mirror plane showed better crystallinity and high surface area, 13 $m^2/g$. $LaMnAl_{11}O_{19}$ revealed well developed plate-like structure which is characteristic structure of hexaaluminate. The catalytic activity of methane combustion increased in the following order: $LaMnAl_{11}O_{19}$ > $SrMnAl_{11}O_{19}$ > $BaMnAl_{11}O_{19}$ and was dependent on surface area of catalysts. 60 wt% $CeO_2/LaMnAl_{11}O_{19}$ calcined at $700^{\circ}C$ showed enhanced methane activity and methane was oxidized completely at low temperature ($700^{\circ}C$). It was confirmed that addition of ceria seems to be effective for the low and middle temperature combustion of methane. But, after calcination at high temperature of $1,200^{\circ}C$, it lost the promoting effect of ceria due to increase of ceria particle size and it had a limit to applying to the high temperature catalytic combustion.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.3 no.4
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• pp.183-192
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• 1998

The long-term observation of temperature in the coastal waters adjacent to the Wolsung Nuclear Power Plant has been carried out from November 10, 1996 to August 22, 1997, for approximately 280 days using a real-time temperature measurement buoy system. The sea-surface temperature was measured at every 10 minute using 10 buoys. The vertical structure of temperature was investigated near the outlet of the plant with two thermistor chains equipped with 10 sensors at 1 m interval The monthly averaged temperature was the lowest with spatial average of $12.8^{\circ}C$ in February and was the highest in August with spatial average of $19.6^{\circ}C$. The extremely low temperature was frequently observed between June and August, which seems to be the consequence of the intrusion of cold water near the southeastern coast of Korea. Distributions of the daily and hourly averaged temperature show that the highest temperature always occurred near the outlet of the plant and the warm-water patch moved along the north-south direction with the semidiurnal period. The semidiurnal fluctuation of temperature was also observed near the surface of the vertical profiles. The spectral analysis of temperature between February and April 1997 shows that the semidiurnal components prevailed near the outlet. It is likely that the semidiurnal components were due to the prevailing semidiurnal tide in this region. In August 1997, the diurnal components were dominant at the surface water of all stations except Station 12, which suggests that the warm water from the outlet of the plant has less effects in summer on the surrounding waters than the strong solar radiation.