• Journal of the Korean Ceramic Society
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• v.56 no.5
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• pp.497-505
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• 2019

Lanthanum-based transition metal cations containing perovskites have emerged as potential catalysts for the intermediate-temperature (600-800℃) oxygen reduction reaction (ORR). Here, we report a facile acetylacetone-assisted combustion route for the synthesis of nanostructured La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δ (LSCF6428) cathodes for intermediate-temperature solid-oxide fuel cells (IT-SOFCs). The as-prepared powder was analyzed by thermogravimetry analysis-differential scanning calorimetry. The powder calcined at 800℃ was characterized by X-ray diffraction, scanning electrode microscopy, energy dispersive X-ray spectroscopy, and Brunauer-Emmett-Teller surface area measurements. It was found that the porosity of the air electrode significantly increased by utilizing the nanostructured LSCF6428 instead of commercial powder. The performance of a single cell fabricated with the nanostructured LSCF6428 cathode increased by 112%, from 0.4 to 0.85 W cm^-2, at 700℃. Electrochemical impedance spectroscopy showed a considerable reduction in the area-specific resistance and activation energy from 133.5 to 61.5 kJ/mol, resulting in enhanced electrocatalytic activity toward ORR and overall cell performance.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.16 no.6
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• pp.273-277
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• 2006

High velocity of oxy-fuel (HVOF) thermal spray coating is progressively replacing the other classical hard coatings such as chrome plating and ceramic coating by the classical methods, since the very toxic $Cr^{6+}$ ion is well known as carcinogen causing lung cancer, and the ceramic coatings are brittle. Co-alloy T800 powder is coated on the Inconel 718 substrates by the HVOF coating procesess developed by this laboratory. For the study of the possibility of replacing of chrome plating, the wear properties of HVOF Co-alloy T800 coatings are investigated using the reciprocating sliding tester with a counter sliding SUS 304 ball both at room and at an elevated temperature of $1000^{\circ}F\;(538^{\circ}C)$. The possibility as durability improvement coating is studied for the application to the high speed spindles vulnerable to frictional heat and wear. Wear mechanisms at the reciprocating sliding wear test are studied far the application to the systems similar to the sliding test such as high speed spindles. Wear debris and frictional coefficients of T800 coatings both at room and at an elevated temperature of $538^{\circ}C$ are drastically reduced compared to those of non-coated surface of Inconel 718 substrates. Wear traces and friction coefficients of both coated and non-coated surfaces are drastically reduced at a high temperature of $538^{\circ}C$ compared with those at room temperature. These show that the coating is highly recommendable far the durability Improvement coating on the surfaces vulnerable to frictional heat and wear.

• Transactions of the Korean hydrogen and new energy society
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• v.21 no.3
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• pp.201-206
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• 2010

In present work, $La_{0.8}Ca_{0.2}CrO_3$ (LCC) ceramic interconnect layer for SOFC was prepared by using thermal plasma spray coating process. The LCC powders were synthesized by Pechini method and calcined at the temperature of $1000^{\circ}C$. The prepared LCC powder was characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM), particle counter, BET analysis, respectively. In addition, basic and essential properties of LCC layer coated by thermal plasma spray coating process such as the morphology of surface and cross section for coated layer, gas leak rate, and electrical conductivity were analyzed and discussed. Based on these experimental results, it can be concluded that the LCC layer coated by thermal plasma spray coating process can be suitable as a ceramic interconnect of SOFC operated at $800^{\circ}C$.

• Resources Recycling
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• v.27 no.2
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• pp.32-37
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• 2018

This study was conducted as a preliminary study for the recycling of palladium and palladium oxide. In this study, thermodynamic equations for the formation of palladium oxide (PdO) are established. Palladium chloride is dissolved into hydrochloric acid to generate a palladium chloride solution. Nanosized palladium oxide powder with an average particle size below 30 nm were generated from this raw material solution by means of a spray pyrolysis process. The palladium oxide particles were composed of a single solid crystal. The results of XRD analysis showed that only a PdO phase of the generated powder was formed. And, the specific surface area of the generated palladium powder was approximately $32m^2/g$.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.17 no.4
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• pp.42-50
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• 2008

Various researches to reduce weight of a vehicle are achieving. One of these researches is tendencious to manufacture the hollow piston rod using friction welding instead of solid one of the vehicle shock absorber. This study deals with the friction welding of SM45C to SM20C-pipe that is used normally in the vehicle shock absorber. The friction time was variable conditions under the conditions of spindle revolution of 2,000rpm, friction pressure of 55MPa, upset pressure of 75MPa, and upset time of 2.0seconds. Under these conditions, the microstructure of weld interface, tensile fracture surface and mechanical tests of friction weld were studied and so the results were as follows. When the friction time was l.5seconds under the conditions, the maximum tensile strength of the friction weld happened to be 837MPa, which is 113% of SM20C's tensile strength and 97% of SM45C's. The optimal welding conditions were n=2,000rpm, $P_1=55MPa$, $P_2=75MPa$, $t_1=1.5sec$, $t_2=2.0sec$ when the total upset length is 1.7mm.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 1997.11a
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• pp.10-11
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• 1997

고체 추진제를 사용하는 추진 시스템을 개발하는데 가장 커다란 문제로 인식되고 있는 것은 추진제의 연소 특성을 이해하는 일이다. 그 중에서도 연소실의 압력 진동과 추진제 벽면으로 흡수되는 복사 열전달에 의한 연소율(burning rate)의 변화로 인하여 발생하는 연소 불안정에 대한 이해는 아직도 완전히 규명되지 않고 있다. 고체 추진제의 연소 불안정에 대한 이론적 해석은 준-정상 1차원 해석(Quasi-Steady Homogeneous One-Dimension) 방법에 의하여 단순화된 지배방정식을 해석하는 것이 일반적으로 잘 알려져 있는 방법이다. 이 가정은 고체 추진제가 연수되는 영역을 두께가 매우 얇은 영역의 표면반응영역(surface reaction layer)과 화학반응이 없는 응축상태영역(condensed phase zone) 그리고 기체상태의 연료와 화염이 존재하는 기체상태영역(gas phase zone) 등의 3영역으로 구분하며, 기체상태영역에서 발생하는 교란에 대한 응축상태영역의 반응시간 크기(response time scale)가 매우 크기 때문에 응축상태영역의 반응은 준 정상적으로 일어난다고 가정하는 것이다.그러나, 연소실의 온도가 $3000^{\circ}K$ 정도의 높은 온도이어서 복사 열전달에 의한 고체 추진제의 가열이 중요한 열전달 방법으로 작용하게 되므로 이를 무시한 이론적 해석은 물리적인 중요성이 약하여질 수밖에 없다. 본 연구에서는 기체영역으로부터 전달되는 복사 열전달은 투명(transparent)한 표면반응영역을 통과하여 응축상태영역에서 모두 흡수되며 추진제 표면에서의 복사열방출(emission)을 고려하였다. 또한 연소불안정 현상을 해석하기 위하여 표면반응영역에서의 경계조건은 선형교란량으로 대치하는 Zn(Zeldovich-Novozhilov) 방법을 사용하였다. 이 방법은 기체상태영역에 대한 구체적인 해석없이도 연소불안정 현상을 해석할 수 있는 장점이 잇다. 즉 응축상태영역에서의 연소율과 표면온도는 각각 기체영역으로부터 전달되는 온도구배와 연소압력, 그리고 복사 열전달의 함수관계이므로 선형교란에 의한 추진제표면에서의 교란경계조건을 얻을 수 잇으며, 응축영역의 교란지배방정식과 함께 사용하여 압력교란과 복사 열전달의 교란에 대한 연소율의 교란 증감 여부를 판단하여 연소 불안정 현상을 해석할 수 있다.

• Korean Journal of Optics and Photonics
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• v.20 no.5
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• pp.276-280
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• 2009

A Cr:YAG crystal was used as a saturable absorber for passive Q-switching of a Nd:$YVO_4$ laser which was pumped by a 1-W continuous wave laser diode. The first surface of the Cr:YAG was high-reflection coated for the pump wavelength. The high-reflection coating improved the absorption efficiency of the pump beam in the Nd:$YVO_4$ through double pass absorption. It also prevented pump beam induced partial bleaching of the Cr:YAG. The peak-to-peak pulse fluctuation of passively Q-switched laser output was approximately 4 %. The minimum pulse-width was measured to be 7.11 ns. Also, the average pulse repetition rate was 9 kHz and the maximum output power was 16.27 mW.

• Korean Journal of Agricultural Science
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• v.29 no.1
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• pp.1-7
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• 2002

Postharvest characteristics of 'Pingguoli' fruit produced between China and Korea were compared to find an ecological difference. There was a difference in fresh weight per fruit, thus, fruit weight produced in Korea was much higher than those in China. However, no significant differences were confirmed in the level of soluble solid content and flesh firmness. The acidity of Korean 'Pingguoli' was higher than Chinese ones. The external appearance of Korean 'Pingguoli' was not attractive due to the rough and rugged surface. Thus, the prospect of 'Pingguoli' cultivation in Korea seems not to be promised. The general trend of respiration and ethylene evolution during storage did not significantly differed but the amount of $CO_2$ and ethylene production was higher in fruits produced in China. There was a strong similarity in respiration and ethylene evolution pattern to typical climacteric fruits. Thus, 'Pingguoli' is considered as a climacteric fruit. Even though the rate of ethylene production of 'Pingguoli' was relatively high, the storability of 'Pingguoli' showed a strong potential. The further studies in postharvest physiology of pear using 'Pingguoli' and in its breeding potentials as a source of long storage life are needed.

• Advances in pediatric surgery
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• v.2 no.1
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• pp.64-67
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• 1996

Aberrant migration of thymic tissue occurs as an ectopic thymus in the mediastinum, base of skull, tracheal bifurcation, and cervical region. A recent review of the literature by Nowak et al. showed over 70 reported cases of aberrant thymus or thymic cyst in patients who presented with primary neck masses. Authors experienced a case of ectopic cervical thymus and reviewed the literature. A one-year-old boy with left neck swelling which had been noticed since one month of age visited out patient clinic. Ultrasonography showed a well-defined cystic mass containing homogeneous, low-echogenic content locating in the lateral aspect of the left carotid sheath. Operation was performed under the impression of branchial cleft cyst. At surgery, a multiseptated, well-encapsulated, brownish and doughy mass which was extending into the vicinity of the carotid bifurcation with sland stalk-like portion ending between the hypoglossal nerve and external carotid artery was excised completely. The cut-surface showed homogenous solid mass, and on frozen section the tissue revealed a normal thymic histology. Postoperative ultrasonography showed bilateral thymus in the superior mediastinum. The patient has no immunologic problem and is doing well now.

• Culinary science and hospitality research
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• v.7 no.2
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• pp.181-194
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• 2001

Dried noodles was manufactured by wheat flour and saline solution mixture. At this time, saline solution mixture was used for simple saline solution and mixture(blending ratio of PNSO and emulsifier=2:1, w/w) of both pine needle seasoning oil (PNSO) manufactured by autoclaving method and food emulsifier. Water absorption ratio, volume expansion ratio and water soluble solid matters content were decreased, but cooking time was prolonged, respectively. According to, suitable treating amount of PNSO was 2-3%(w/w) level. On organoleptic test, the peculiar green color was appeared in cooked noodles of PNSO treating groups. The surface was slickly, chewy rheology and texture were improved at PNSO treating cooked noodle. During 20-30 minutes after cooking, chewy characteristics was maintained the treating groups more than PNSO 2%(w/w). At the result, this PNSO treatin dried noodle samples were suitable at the institutional food service as well as dining hal1 for the case of large scale's kitchen work.