• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2001.11a
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• pp.28-28
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• 2001

$Bi_2Te_3$계 열전반도체 재료는 200 ~ 400K 정도의 저온에서 에너지 변환 효율이 가장 높은 재료로서 열전냉각 및 발전재료로 제조볍 및 특성에 관한 많은 연구가 진행되어 왔다. 전자냉각 모듈의 제조에는 P형 및 N형 $Bi_2Te_3$계 단결정이 주로 사용되고 있으나. $Bi_2Te_3$ 단결정은 C축에 수직한 벽개면을 따라 균열이 쉽게 전파하기 때문에 소자 가공사 수윤 저하가 가장 큰 문제점으로 지적되고 있다. 이에 따라 최근 열전재료의 가공방법에 따른 회수율 증가 및 열전특성 향상에 관한 열간압출, 단조와 같은 연구가 활발히 이루어지고 있다. 본 연구는 가스분사법(gas atomizer)을 이용하여 용질원자 편석의 감소, 고용도의 증가,균일고용체 형성, 결정립미세화 둥 급속응고의 장점을 이용하여 화학적으로 균질한$Bi_2Te_3$계 열전재료 분말을 제조하고, 제조된 분발을 압출가공하여 기계적성질, 소자의 가공성 및 열전 성능 지수율 향상시키는데 연구 목적이 있다. 본 설험에서는 99.9%이상의 고순도 Bi. Te. Se. Sb를 이용하여, 고주파 유도로에서 Ar 분위기로 용융하고, 가스분사법를 이용하여 균질한 $Bi_2Te_3$계 열전재료 분만을 제조하였다. 분말표면의 산화막을 제거하기 위하여 수소분위기에서 환원처리를 행하였고, 된 분말을 Al 캔 주입하여 냉간성형 한 후 진공중에서 압출온도를 변화시켜 열간압출 가공을 행하였다. 압출 온도변화에 따른 압출재의 미세조직 및 열전특성에 중요한 영향을 미치는 C면 배향에 대한 결정방위 해석, 압출재의 압축강도 등을 분석하였으며, 압출온도에 따삼 미세조직 변화와 결정방위의 변화에 따른 열전특성의 관계를 해석하였다성시켰고 이들이 산인 HNO3에서 녹았기 때문이다. 본 연구에서 개발된 새로운 에칭 용액인 90H2O2 - 10HNO3 (vol%)의 에칭 원리가 똑같이 적용 가능한 다른 종류의 초경 합금에서도 사용이 가능할 것으로 판단된다.로 판단된다.멸과정은 다음과 같다. 출발물질인 123 분말이 211과 액상으로 분해될 때 산소가스가 배출되며, 이로 인해 액상에서 구형의 기공이 생성된다. 이들 중 일부는 액상으로 채워져 소멸되나, 나머지는 그대로 남는다. 특히, 시편 중앙에 서는 수십-수백 마이크론 크기의 커다란 기공이 다수 관찰된는데, 이는 기공의 합체로 만들어진 것이다. 포정반응 열처리 시 기공 소멸로 만들어진 액상포켓들은 주변 211 입자와 반응하여 123 영역으로 변한다. 이곳은 다른 지역과 비교하여 211 밀도 가 낮기 때문에, 미반응 액상이 남거나 211 밀도가 낮은 123 영역이 된다. 액상으로 채워지지 못한 구형의 기공들 중 다수가 123 결정 내로 포획되며, 그 형상은 액상/ 기공/고상 계면에너지에 의해 결정된다.단의 경우, 파단면이 매끄럽고 파변상의 결정립도 매우 미세하였으며, 산확물 의 용집도 찾아보기 어려웠 나, 접합부 파단의 경우에는 파변의 굴곡이 비교척 심하고 연성 입계파괴의 형태를 보였￡며, 결정립도 모채부 파단의 경우에 비해 조대하였다. 조대하였다. 셋째, 주상기간 중 총 에너지 유입률 지수와 $Dst_{min}$ 사이에 높은 상관관계가 확인되었다. 특히 환전류를 구성하는 주요 입자의 에너지 영역(75~l13keV)에서 가장 높은(0.80) 상관계수를 기록했다. 넷째, 회복기 중에 일어나는 입자들의 유입은 자기폭풍의 지속시간을 연장시키는 경향을 보이며 큰 자기폭풍일수록 현저했다. 주상에서 관측된 이러한 특성은 서브스톰 확장기 활동이 자기폭풍의

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.4
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• pp.578-585
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• 2018

This paper proposes a design method for a 3-phase interior permanent magnet synchronous motor (IPMSM) and clamping force control method for an electro-mechanical brake (EMB) using co-simulation for a high-speed train (HST). A traditional pneumatic brake system needs much space for the compressor, brake reservoir, and air pipe. However, an EMB system uses up to 50% less space due to the use of a motor and electric wires for controlling the brake caliper. In addition, it can reduce the latency time for brake control because of the fast response and precise control. A train that has many brakes is advantageous for safety because of the control by sharing the braking force. In this paper, a driving method for a cam-shaft-type EMB is modeled. It is different from the ball-screw-type brakes that are widely used in automobiles. In addition, a co-simulation method is proposed using JMAG and Matlab/Simulink. The IPMSM was designed and analyzed with the JMAG tool, and the control system was simulated using Matlab/Simulink. The effectiveness of the co-simulation results of the mechanical clamping force and braking force was verified by comparison with the clamping force specifications of a HEMU-430X HST.

• Food Engineering Progress
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• v.22 no.4
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• pp.381-385
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• 2018

Various rheological methods to measure the hardness of instant cooked rice by a texture analyzer were investigated and compared. Specifically, instant white rice samples with a wide range of hardness were subjected to four different rheological tests with disk, cylinder, rod, and cone probe whose results were inter-correlated. All the measurements demonstrated that the hardness of instant rice was reduced with increasing moisture content and showed negatively linear relationships. Out of the four tests applied in this study, the highest coefficient of correlation ($R^2=0.9268$) was observed distinctly in the cone probe test, where both compressive and shear forces can be applied to deform individual rice grains. However, the cylinder probe test had the lowest coefficient of correlation ($R^2=0.7247$) because it may be ineffective in causing direct deformation of individual rice grains. Furthermore, when the hardness values (N) were converted to stress (Pa), highly linear correlations ($R^2{\approx}0.99$) were observed between the tests with similar probe geometry and force application.

• Applied Chemistry for Engineering
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• v.28 no.1
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• pp.101-111
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• 2017

Mineral carbonation is a technology in which carbonates are synthesized from minerals including serpentine and olivine, and industrial wastes such as slag and cement, of which all contain calcium or magnesium when reacted with carbon dioxide. This study aims to develop the mineral carbonation technology for commercialization, which can reduce environmental burden and process cost through the reduction of carbon dioxide using steel slag and the slag reuse after calcium extraction. Calcium extraction was conducted using NH4Cl solution for air-cooled slag and convert slag, and ${\geq}98%$ purity calcium carbonate was synthesized by reaction with calcium-extracted solution and carbon dioxide. And we conducted experimentally to minimize the quantity of by-product, the slag residue after calcium extraction, which has occupied large amount of weight ratio (about 80-90%) at the point of mineral carbonation process using slag. The slag residue was used to replace silica sand in the manufacture of cement panel, and physical properties including compressive strength and flexible strength of panel using the slag residue and normal cement panel, respectively, were analyzed. The calcium concentration in extraction solution was analyzed by inductively coupled plasma optical emission spectrometer (ICP-OES). Field-emission scanning electron microscope (FE-SEM) was also used to identify the surface morphology of calcium carbonate, and XRD was used to analyze the crystallinity and the quantitative analysis of calcium carbonate. In addition, the cement panel evaluation was carried out according to KS L ISO 679, and the compressive strength and flexural strength of the panels were measured.

• Journal of Korean Society of Forest Science
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• v.29 no.1
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• pp.1-19
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• 1976

This study has been made to make an observation regarding present status of the coal mine props which is desperately needed for coal production, despite of great shortage of the timber resources in this country, and investigate the effects of diffusion process on the decay resistances of the mine props as applied preservatives of Malenit and chromated zinc chloride. The results are as follows. 1. Present status of the coal mine props Total demand of coal mine props in the year of 1975 was approximately 456 thousand cubic meters. The main species used for mine props are conifer (mainly Pinus densiflora) and hardwood (mainly Quercus). Portions between them are half and half. With non fixed specification, wide varieties of timber in size and form are used. And volume of wood used per ton-of coal production shows also wide range from 0.017 cubic meter to 0.03 cubic meter. 2. Decay resistance test a) The oven dry weight decreased between untreated specimen and treated specimen has not shown any significantly, although it has shown some differences in average values between them. It may be caused by the shorter length of the test. b) The strength of compression test between untreated specimen and treated specimen has also shown the same results as shown in case of weight decrease. Reasons assumed are the same. c) The amounts of the extractives in one percent of sodium hydroxide (NaOH) between untreated and treated specimen have shown the large value in case of untreated specimen than that of treated. 3. The economical benifit between untreated and treated wood when applied in field has seen better in long term base in case of treated wood, although the primary cost of treated wood add a little bit more cost than that of the untreated wood.