• Journal of the Korean Crystal Growth and Crystal Technology
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• v.10 no.2
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• pp.111-115
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• 2000

$BaTIO_3$ thin films were prepared on (100) $BaTIO_3$ substrates by coating- pyrolysis process using metal-organic compounds of Ba and Ti. The amorphous films prefired at $450^{\circ}C$were crystallized above $700^{\circ}C$ under oxygen partial pressure of $2\times 10^{-4}$. The lattice parameters of the perpendicular axis for the $BaTIO_3$ thin films heat-treated below $800^{\circ}C$ were closer to a value of cubic $BaTIO_3$, whereas those above $800^{\circ}C$ were closer to a value of tetragonal BaTiG. The results of XRD P scan and pole-figure analyses indicated that BaTiO, thin films have an epitaxial relationship with the $SrTiO_3$ substrates. The $BaTIO_3$thin films annealed at$800^{\circ}C$ showed the surface with island-like grains about 0.4$mu \textrm{m}$ and the cross section of 0.8 $mu \textrm{m}$ thickness with granular grains.

• Economic and Environmental Geology
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• v.37 no.4
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• pp.375-381
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• 2004

Pyrochlore was known as one of the most promising materials for the immobilization of radioactive actinide. This study includes the synthesis, phase relation and characteristics of pyrochlores (CaCeH$f_xTi_{2-x}O_7$=0.2, 0.6, 1.0, 1.4, 1.8, 2.0) in the system of Ca-Ce-Hf-Ti-O. The samples were prepared from high purity of starting materials under the pressure of 400kg/cm$^2$ at room temperature, and were sintered at 1200∼1$600^{\circ}C$ The synthesized samples were analyzed and identified with XRD. The optimal formation conditions of pyrochlores were at 1300∼150$0^{\circ}C$ under $O_2$ atmosphere with batch compositions. During synthesis, pyrochlore, perovskite and $A_{2}BO_{5}$ oxide were formed. The characteristics of this system is that parameter of pyrochlore was increased with the content of hafnium. This phenomenon was due to the difference of ionic size between hafnium and titanium in six coordinated site.

• Journal of the Korean Ceramic Society
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• v.34 no.2
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• pp.139-144
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• 1997

Structurally, the rare earth cuprate superconductor of Nd2-xCexCuO4-$\delta$ has T' structure and has been known as having a quite complicated microstructural phenomena, so far. In order to be superconductivity, both small amount of cation substitution of Nd3+ by Ce4+ and oxygen reduction are required. In the present study the crystallographic study on the structural transition for the Nd2-xCexCuO4-$\delta$ crystal has been con-ducted by observing the CBED (Convergent Beam Electron Diffraction) pattern with STEM(Scanning Transmission Electron Microscope). Three different samples of Nd2CuO3,Nd1.85Ce0.15CuO4 and Nd1.85Ce0.15CuO3.965 were prepared by solid-state sintering and their CBED patterns were observed by STEM to study the structural transition accompanying the substitution of Ce and the reduction of oxygen. Experimental HOLZ lines of these samples were compared with those plotted by a computer-programmed simulation to de-termine the lattice parameter of Nd2-xCexCuO4-$\delta$ crystal.

• Journal of the Korean Ceramic Society
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• v.41 no.1
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• pp.36-40
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• 2004

$SnO_2$ thin films were deposited on a $SiO_2$/Si substrate with the flow of Ar and $O_2$ of 25 sccm by RF-magnetron sputtering method. the post-annealing was conducted at $500^{\circ}C$ in atmosphere of dry air and $N_2$ were changed fairly, while those annealed in dry air resembled as-deposited films. This may be attributed to the desorption of adsorbed oxygen and the extraction of lattice oxygen during annealing. Resistivity of films annealed in $N_2$ was increased over 5 times than that of as-deposited films. It can be explained that the increment of resistivity may result from the discontinuous conduction path with change of microstructures after annealing in $N_2$.

• Proceedings of the Korean Environmental Sciences Society Conference
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• 2003.05a
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• pp.249-254
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• 2003

분석에 이용된 격자망은 동곡, 고로, 미성, 병천, 효령 및 무성지점에 각각 12개, 30개, 45개, 76개, 46개 및 1265개의 조격자를 구성하였으며 하천의 수로방향 및 경사형태를 세분화하기 위하여 각 지점에 대하여 8개, 24개, 24개, 44개, 12개 및 64개의 세격자로 분할하였다. AGNPS를 이용한 첨두유량의 모의발생 결과치가 동곡, 고로, 미성, 병천, 효령 및 무성지점에서 측정값과 비교하여 각 호우사상별로 상대오차가 1.0~25.0%, 4.0~27.0%, 7.0~29.2%, 2.0~23.9%, 3.0~25.0% 및 3.6~21.0%의 차이를 나타내었다. 분석결과에서 AMCII조건에서는 관측치와 분석결과치가 유사하게 나타났으나 AMCI조건에 대해서는 상대적으로 작은 값을 보였으며 AMCIII조건에서는 다소 큰 값으로 분석되었다. SCS방법에서 제안하는 AMC조건별 CN값을 우리 실정에 적합하도록 수정 보완하기 위한 수정 유출곡선지수 $CN_{m}$ /I과 $CN_{m}$/III을 재구성하였으며, 여기에 적용되는 수정 유출 곡선지수식의 계수 a를 추정한 결과, 기왕에 발표된 연구결과와 거의 일치된 경향을 나타내었다. 제안된 수정 CN식을 이용하여 산정한 결과치와 관측치는 거의 유사하게 나타났다. AGNPS모델에 의한 유출량 산정에 있어 수문학적 토양피복형수(CN)의 결정을 위하여 선행강우량과 토양의 공극율 및 지형인자인 각 셀마다의 유역경사를 이용하여 관계식(CN =f($X_1$, $X_2$, $X_3$))을 유도하였으며, 분석 결과에서 CN이 선행강우량과 가장 밀접한 관계가 있음을 알 수 있었으며 유역경사, 토양의 공극율 순으로 나타났다..88mg/$\ell$~의 범위로 나타났다. 무태교 지점에서의 총인의 농도는 0.52mg/$\ell$~0.99mg/$\ell$~의 범위이었다. 신천에 금호강물을 혼합한 이후에도 부유물질, 생화학적산소요구량, 암모니아태 질소, 총인 등의 농도가 개선되지 않았다. 즉 금호강물의 혼합은 신천수질환경사업소에서 배출되는 방류수에 함유되어 있을 2차 오염물질의 희석이라는 이점외의 수질개선효과는 확인되지 않았다.l years and a new type of transfer crane has been developed. Design concepts and control methods of a new crane will be introduced in this paper.and momentum balance was applied to the fluid field of bundle. while the movement of′ individual material was taken into account. The constitutive model relating the surface force and the deformation of bundle was introduced by considering a representative prodedure that stands for the bundle movement. Then a fundamental equations system could be simplified considering a steady state of the process. On the basis of the simplified model, the simulation was performed and the results co

• Fire Science and Engineering
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• v.33 no.4
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• pp.35-40
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• 2019

In this study, the mass flow rate of the heat release rate equation, which is the major factor of the oxygen consumption method, was analyzed for the fundamental investigation of the cone-calorimeter (5 m length and 0.3 m diameter). The shapes of a completely empty inside, 3 mm pore diameter mesh and pore diameter 10 mm honeycomb with 0.76 porosity were constructed using the cone-calorimeter. To calculate the mass flow rate, four bi-directional probes and thermocouples were installed in a uniform position in the vertical direction of flow. The velocity gradient and flow perturbation were measured from the increase in Reynolds number. As the flow capacity increased, the speed gradient increased in all three shapes relative to the turbulence intensity. In addition, the deviation of extended uncertainty to the mass flow was completely low in the order of empty space, mesh (d_p = 3 mm) and honeycomb (d_p = 10 mm and 𝜖 = 0.76) at the 95% confidence level. The results can be used in designs to improve the flow stability of the cone calorimeter.

• Journal of the Korean Society of Propulsion Engineers
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• v.16 no.5
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• pp.37-46
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• 2012

The calculation model for heat transfer analysis of rocket engine combustion chamber considering film-cooling has been established. Convective, radiative heat transfers and film-cooling effect in combustion chamber were evaluated using empirical equations especially for rocket engine combustors, and for heat transfer outward from chamber wall general convective and radiative equations were applied. Structural grid has been generated inside chamber wall for FVM calculations, and transient thermal analyses were carried out by time-marching techniques. LOx/kerosene rocket engine with chamber pressure of 50 bar has been analysed, and it is shown that, in that case, the film-cooling less than 4% remarkably contributes to reduce wall temperature, but the effect of the effect of film-cooling more than about 4% is not significantly increased.

• Journal of the Korean Chemical Society
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• v.28 no.2
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• pp.102-108
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• 1984

The catalytic oxidation of CO has been investigated on $ZnCe_{1+y}O_2$ at temperatures from 300 to $500^{\circ}C$ under various P_{CO} and PO_2 conditions. The oxidation rates have been correlated with 1.5-order kinetics: first order with respect to CO and 0.5 order with respect to O2. CO appears to be absorbed essentially on the O lattice of $ZnCe_{1+y}O_2$ as a molecular species, while $O_2$ adsorbs on an O vacancy as an ionic species. The conductivity data show that CO adsorption contributes electron to the conduction band and the adsorption process of $O_2$ withdraws it from an O vacancy. The oxidation mechanism and the defect model of $ZnCe_{1+y}O_2$ are inferred at given temperature and $PO_2'$s from the agreement between the conductivities and kinetic data. It is suggested that CO absorption is the rate-controlling.

• New & Renewable Energy
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• v.2 no.2 s.6
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• pp.69-74
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• 2006

본 연구는 페라이트의 Fe 양이온 일부를 Ni, Mn, Co등으로 치환하여 M-ferrite를 제조하여 열화학적 2단계 물 분해 반응의 특성을 비교 평가하였고, XRD, SEM, GC등의 분석으로 각 금속산화물의 특성을 확인하였다. M-ferrites 는 고상법으로 제조하였다. 각각의 M-ferrite에 대한 열적환원은 1573K 에서 진행하였고 물 분해 반응은 1273K 에서 실시하였다. 이 반응에서 생성된 가스는 전량 포집하여 GC를 통해 분석하였다. 반응 전후의 시료에 대하여 SEM, XRD를 분석하여 GC결과와 함께 금속산화물의 산화환원반응 특성을 고찰하였다. 그 결과로서 물 분해 반응 후 M-ferrite (M=Co, Ni, Mn)의 생성을 XRD를 통하여 확인할 수 있었고, 물 분해 반응과의 비교결과 격자상수의 증대가 M-ferrite내의 산소의 환원에 영향을 미치는 것을 알 수 있었다. SEM결과에서는 4cycle의 물 분해 반응 후 Mn-ferrite의 심한 sintering 현상을 확인 할 수 있었다.

• Korean Journal of Materials Research
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• v.16 no.5
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• pp.323-328
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• 2006

In situ electrical conductivity measurements on $V_2O_5WO_3/TiO_2$ catalysts were carried out at between 100 and $300^{\circ}C$ under pure oxygen, NO and $NH_3$ to investigate the reaction mechanism for ammonia SCR (selective catalytic reduction) de NOX. The electrical conductivity of catalysts changed irregularly with supply of NO. It was, however, found that the electrical conductivity change with ammonia supply was regular and the increase of electrical conductivity was mainly caused by reduction of the labile surface oxygen. The electrical conductivity change of catalysts showed close relationship with the conversion rate of NOx. Variation of conversion rate in atmosphere without gaseous oxygen also showed that labile lattice oxygen is indispensable in the initial stage of the de NOx reaction. These results suggest that liable lattice oxygen acts decisive role in the de NOx mechanism. They also support that de NOx reaction occurs through the Eley?Rideal type mechanism. The amount of labile oxygen can be estimated from the measurement of electrical conductivity change for catalysts with ammonia supply. This suggests that measurement of the change can be used as a measure of the de NOx performance.