• 한국산학기술학회논문지
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• 제8권5호
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• pp.1042-1046
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• 2007

본 연구에서는 제 3의 화학 원소 첨가에 의한 코발트 실리사이드와 니켈 실리사이드의 열적 안정성 향상 메카니즘을 조사하였다. 즉, Co-Si 시스템에 텅스텐을 첨가하는 경우 CoSi의 heat of formation이 증가하는 것으로 관찰되었다. 이러한 증가는 시스템 에너지 감속 속도의 최대화로 대변되는 실리사이드 형성 kinetics가 선호하는 glass의 형성을 억제하는 것으로 밝혀졌다. 이 경우 CoSi와 실리콘 기판 사이의 계면에 형성되는 다결정 구조는 glass의 self-diffusion보다 확산계수가 훨씬 작아 상 변이를 위해서는 보다 높은 열에너지를 요구하게 되어 궁극적으로 CoSi의 열적 안정성이 향상되는 것을 알 수 있었다.

• Nuclear Engineering and Technology
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• 제27권4호
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• pp.463-469
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• 1995

궤환효과의 지배를 받는 점동특성시스템은 특정 운전조건에서 여러 개의 정상상태해를 가질 수 있다. 점동특성시스템의 다중해 및 비선형시스템의 일반적인 특성과 관련된 이론적 연구를 통하여, 점동특성시스템이 주어진 외부 입력 반응도에 대해 다중의 정상상태해를 갖기 위한 필요충분조건을 얻었다. 즉 정상상태에서의 궤환반응도가 제환변수의 어떤 값에 대해서 'Strictly Monotoruc'이 아니면, 점동특성시스템은 그 값에 대응되는 운전영역에서 다중의 정상상태해를 갖는다. 반면 정상상태에서의 궤환반응도가 궤환변수의 모든 값에 대해서 'Strictly Monotonic' 이면, 점동특성시스템은 항상 하나의 정상상태해를 갖는다.

• 한국재료학회지
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• 제3권3호
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• pp.276-281
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• 1993

3원계 U-Ce-O산화물의 소결거동을 연구하기 위하여 $UO_2$ 및 $CeO_2$분말을 ball-mill 방법으로 혼합한 (U, Ce)$O_2$의 영향이고, 나중에 나타나는 극대점은 $CeO_2$의 영향 때문이다. 또한 $Ceo_{2}$함량이 증가할수록 소결이 지연됨을 알수 있었다. 동일한 10wt. % $CeO_2$함량에서, 4시간동안 ball-milling을 하였을때가 소결속도는 가장 빨랐다.

• 한국추진공학회지
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• 제22권4호
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• pp.55-60
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• 2018

열적 특성은 에너지 물질 분야에서 중요한 특성 중 하나로, 분해열을 방출하기 때문에, 열적 특성 분석에 DSC(Differential Scanning Calorimetry)가 자주 사용된다. 그러나 DSC 측정의 경우, 용융과 같은 열역학적 변화가 kinetics 분석에 방해를 끼친다. 이번 연구에서는 이 문제점을 해결하는 방안으로, 등온 조건으로 한 DSC 기초 데이터와 g 단위로 측정하는 ARC(Accelerating Rate Calorimetry)의 데이터를 이용하여 AKTS(Advanced Kinetics and Technology Solutions) thermokinetic 프로그램을 이용하여 열적 노화 특성을 예측, 비교한다.

• Advances in Energy Research
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• 제4권3호
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• pp.213-221
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• 2016

The main purpose of this work is to test the validation of use of a four step reaction mechanism to simulate the laminar speed of hydrogen enriched methane flame. The laminar velocities of hydrogen-methane-air mixtures are very important in designing and predicting the progress of combustion and performance of combustion systems where hydrogen is used as fuel. In this work, laminar flame velocities of different composition of hydrogen-methane-air mixtures (from 0% to 40% hydrogen) have been calculated for variable equivalence ratios (from 0.5 to 1.5) using the flame propagation module (FSC) of the chemical kinetics software Chemkin 4.02. Our results were tested against an extended database of laminar flame speed measurements from the literature and good agreements were obtained especially for fuel lean and stoichiometric mixtures for the whole range of hydrogen blends. However, in the case of fuel rich mixtures, a slight overprediction (about 10%) is observed. Note that this overprediction decreases significantly with increasing hydrogen content. This research demonstrates that reduced chemical kinetics mechanisms can well reproduce the laminar burning velocity of methane-hydrogen-air mixtures at lean and stoichiometric mixture flame for hydrogen content in the fuel up to 40%. The use of such reduced mechanisms in complex combustion device can reduce the available computational resources and cost because the number of species is reduced.

• Membrane and Water Treatment
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• 제8권2호
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• pp.161-169
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• 2017

The adsorption of phosphate onto mesoporous $TiO_2$ was investigated in order to reduce phosphorus concentrations in wastewater and provide a potential mode of phosphorus recovery. Three equilibrium isotherms were used to optimize and properly describe phosphate adsorption ($R^2$>0.95). The maximum capacity of phosphate on the adsorbent was found to be 50.4 mg/g, which indicated that mesoporous $TiO_2$ could be an alternative to mesoporous $ZrO_2$ as an adsorbent. A pseudo-second order model was appropriately fitted with experimental data ($R^2$>0.93). Furthermore, the suitable pH for phosphate removal by $TiO_2$ was observed to be in the range of pH 3-7 in accordance with ion dissociation. In contrast, increasing the pH to produce more basic conditions noticeably disturbed the adsorption process. Moreover, the kinetics of the conducted temperature study revealed that phosphate adsorption onto the $TiO_2$ adsorbent is an exothermic process that could have spontaneously occurred and resulted in a higher randomness of the system. In this study, the maximum adsorption using real wastewater was observed at $30^{\circ}C$.

• Environmental Engineering Research
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• 제24권3호
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• pp.513-520
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• 2019

In this investigation, nano ZnO was sonochemically synthesized by a novel method using a methionine precursor. A narrow size distribution (41-50 nm) of nano ZnO was achieved that was immobilized on perlite and applied as a catalyst in catalytic ozonation. The catalyst was characterized by fourier transform infrared spectroscopy, BET surface area, and field emission scanning electron microscope. The ozonation of recalcitrant Remazol black 5 (RB5) di-azo dye solution by means of the synthesized catalyst was investigated in a bubble column slurry reactor. The influence of pH values (7, 9, 11), catalyst dosage (8, 12, 15, $20g\;L^{-1}$) and reaction time (10, 20, 30, 60 min) was investigated. Although the dye color was completely removed by single ozonation at a higher reaction time, the applied nanocatalyst improved the dye declorination kinetics. Also, the degradation of the hazardous aromatic fraction of the dye was enhanced five-times by catalytic ozonation at a low reaction time (10 min) and a neutral pH. The second-order kinetics was best fitted in terms of both RB5 color and its aromatic fraction removal. The total organic carbon analysis indicated a significant improvement in the mineralization of RB5 by catalytic ozonation using the nano-ZnO/perlite catalyst.

• Nuclear Engineering and Technology
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• 제51권3호
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• pp.746-754
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• 2019

Vitrification of radioactive liquid waste (RLW) provides a feasible solution for isolating radionuclides from the biosphere for an extended period. In vitrification, base glass and radioactive waste are added simultaneously into the melter. Determination of heat and mass transfer rates is necessary for rational design and sizing of melter. For obtaining an assured product quality, knowledge of reaction kinetics associated with the thermal decomposition of waste constituents is essential. In this study Thermogravimetry (TG) - Differential Thermogravimetry (DTG) of eight kinds of nitrates and two oxides, which are major components of RLW, is investigated in the temperature range of 298-1273 K in the presence of base glasses of five component (5C) and seven component (7C). Studies on thermal behavior of constituents in RLW were carried out at heating rates ranging from 10 to $40\;K\;min^{-1}$ using TG - DTG. Thermal behavior and related kinetic parameters of waste constituents, in the presence of 5C and 7C base glass compositions were also investigated. The activation energy, pre-exponential factor and order of the reaction for the thermal decomposition of 24% waste oxide loaded glasses were estimated using Kissinger method.

• 한국수소및신에너지학회논문집
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• 제31권6호
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• pp.564-570
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• 2020

Metal hydride is suitable for safe storage of hydrogen. The hydrogen storage kinetics of the metal hydride are highly dependent on its heat transfer characteristics. This study presents a metal hydride-expended graphite composite with improved thermal conductivity and its hydrogen storage kinetics. To improve the heat transfer characteristics, a metal hydride was mixed and compacted with a high thermal conductivity additive. As the hydrogen storage material, AB5 type metal hydride La0.9Ce0.1Ni5 was used. As an additive, flakes-type expended graphite was used. With improved heat transfer characteristics, the metal hydride-expended graphite composite stores hydrogen four times faster than metal hydride powder.

• 한국운동역학회지
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• 제31권1호
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• pp.64-71
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• 2021

Objective: This study investigated the different in isokinetic peak strength of the knee joint, and kinetics and kinematics in drop landing pattern of lower limb between the patellofemoral pain syndrome (PFPS) patients and normal. Method: 30 adult females were divided into the PFPS (age: 23.13±2.77 yrs; height: 160.97±3.79 cm, weight: 51.19±4.86 kg) and normal group (age: 22.80±2.54 yrs, height: 164.40±5.77 cm, weight: 56.14±8.16 kg), with 15 subjects in each group. To examine the knee isokinetic peak strength, kinematics and kinetics in peak vertical ground reaction force during drop landing. Results: The knee peak torque (Nm) and relative strength (%) were significantly weaker PFPS group than normal group. In addition, PFPS group had significantly greater hip flexion angle (°) than normal group. Moreover, normal group had significantly greater moment of hip abduction, hip internal rotation, and left ankle eversion than PFPS group, and PFPS group had significantly greater moment of knee internal rotation. Finally, there was significant differences between the groups at anteroposterior center of pressure. Conclusion: The PFPS patients had weakened knee strength, and which can result in an unstable landing pattern and cause of more stress in the knee joints despite to effort of reduce vertical ground reaction force.