• 한국재료학회지
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• 제32권6호
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• pp.287-292
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• 2022

Magnesium-antimonide is a well-known zintl phase thermoelectric material with low band gap energy, earth-abundance and characteristic electron-crystal phonon-glass properties. The nominal composition Mg_3.8-xZn_xSb₂ (0.00 ≤ x ≤ 0.02) was synthesized by controlled melting and subsequent vacuum hot pressing method. To investigate phase development and surface morphology during the process, X-ray diffraction (XRD) and scanning electron microscopy (SEM) were carried out. It should be noted that an additional 16 at. % Mg must be added to the system to compensate for Mg loss during the melting process. This study evaluated the thermoelectric properties of the material in terms of Seebeck coefficient, electrical conductivity and thermal conductivity from the low to high temperature regime. The results demonstrated that substituting Zn at Mg sites increased electrical conductivity without significantly affecting the Seebeck coefficient. The maximal dimensionless figure of merit achieved was 0.30 for x = 0.01 at 855 K which is 30% greater than the intrinsic value. Electronic flow properties were also evaluated and discussed to explain the carrier transport mechanism involved in the thermoelectric properties of this alloy system.

• 소성∙가공
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• 제20권4호
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• pp.296-302
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• 2011

The objective of this paper is to determine the effect of process parameters on the behavior of a 18Cr-10Mn-$0.44N_2$ nitrogen steel sample deformed by hot rolling. Compression tests were carried out at high temperatures to determine the flow stresses needed for a finite element(FE) analysis. The strain rate, ranging from 0.1 to $1.0s^{-1}$, significantly affected the flow stress at temperatures higher than $1,000^{\circ}C$. Non-isothermal rolling simulations and laboratory rolling tests were performed with plate specimens 14.5mm thick, 135mm wide and 226mm long. A rolling reduction of 15% per pass leading to a cumulative rolling reduction of 60% was determined as optimal. The extension ratio of 176.5% in the length direction was about 30.4 times greater than the extension ratio of 5.8% in the width direction. Isotropic properties for tensile strength, microstructure and grain size were measured after mock-up hot rolling tests. The results from the mockup tests were found to be in good agreement with those of the simulations.

• 폴리머
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• 제36권1호
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• pp.41-46
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• 2012

본 연구에서는 대표적인 난용성 약물이며, 경구용 천식 치료제 중 하나인 pranlukast의 용해도 및 용출성 개선 제제 개발을 위해 친수성 고분자인 poly(ethylene glycol) (PEG)와 고분자 계면활성제인 poloxamer를 사용하여 열용융법(HM)과 용매증발법(SE)에 의한 고체분산체를 제조하였다. 고체분산체 내 약물의 결정성 변화를 DSC, PXRD로 분석한 결과, 약물의 결정성이 크게 감소하였고, 부분적으로 무정형으로 변화하였음을 확인하였다. 용출시험 및 용해도 분석결과, 고유 약물에 비해 용해도와 용출 속도가 크게 증가하였다. Pranlukast, PEG, poloxamer가 1:5:1의 조성으로 열용융법에 의해 제조된 고체분산체가 가장 우수한 용해도 및 용출속도 향상 결과를 보였다. 결과적으로 PEG과 poloxamer를 이용한 고체분산체 제제는 난용성 약물인 pranlukast의 용해도와 생체이용률을 개선하는데 유용하게 응용될 것으로 기대된다.

• 마이크로전자및패키징학회지
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• 제17권2호
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• pp.49-54
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• 2010

n형 $Bi_2(Te,Se)_3$ 분말을 용해/분쇄법으로 제조하여 가압소결 후, 가압소결체의 열전특성을 $Bi_2(Te,Se)_3$ 잉곳과 비교하였으며, $Bi_2(Te,Se)_3$ 열전분말의 기계적 밀링처리가 가압소결체의 열전특성에 미치는 영향을 분석하였다. $Bi_2(Te,Se)_3$ 잉곳은 $24.2{\times}10^{-4}W/m-K^2$의 power factor를 나타내었으며, 이를 가압소결함으로써 power factor가 $27.3{\sim}32.3{\times}10^{-4}W/m-K^2$로 향상되었다. 기계적 밀링처리한 분말로 제조한 $Bi_2(Te,Se)_3$ 가압소결체는 $100^{\circ}C$에서 1.02의 무차원 성능지수를 나타내었으며, $130^{\circ}C$에서 외인성-내인성 천이거동을 나타내었다.

• 한국분말재료학회지
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• 제24권3호
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• pp.202-209
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• 2017

A cold-work tool steel powder is used to fabricate 3-dimensional objects by selective laser melting using a high-pressure gas atomization process. The spherical powder particles form continuous carbide networks among the austenite matrix and its decomposition products. The carbides comprise Nb-rich MC and Mo-rich $M_2C$. In the SLM process, the process parameters such as the laser power (90 W), layer thickness ($25{\mu}m$), and hatch spacing ($80{\mu}m$) are kept fixed, while the scan speed is changed from 50 mm/s to 4000 mm/s. At a low scan speed of 50 mm/s, spherical cavities develop due to over melting, while they are substantially reduced on increasing the speed to 2000 mm/s. The carbide network spacing decreases with increasing speed. At an excessively high speed of 4000 mm/s, long and irregularly shaped cavities are developed due to incomplete melting. The influence of the scan pattern is examined, for which $1{\times}1 mm^2$ blocks constituting a processing layer are irradiated in a random sequence. This island-type pattern exhibits the same effect as that of a low scan speed. Post processing of an object using hot isostatic pressing leads to a great reduction in the porosity but causes coarsening of the microstructure.

• 한국세라믹학회지
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• 제18권4호
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• pp.247-256
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• 1981

Silica bricks had been in arc-furnace roofs of various sizes and steelmaking practices. The resulting materials were examined with reference to mineral and chemical changes. Silica bricks develope definite zones while in service. These zones represent a concentration gradient through the brick that results from the thermal gradient across the brick and from the furnace atmosphere. There are major brick losses by spalling as well as by melting of the hot-face surface in an iron-oxide rich liquid.

• 한국섬유공학회:학술대회논문집
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• 한국섬유공학회 1997년도 춘계학술발표회 논문집
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• pp.328-332
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• 1997

Hot stretching focused on the improvement of properties of poly(L-lactic acid) fiber. Some aliphatic polyesters are biodegradable under microbial attack and the new unique applications are expected. Generally, these materials have a somewhat low melting temperature and low mechanical properties compared with the aromatic polyesters. In this study, melt-spinning of poly(L-lactic acid) was conducted. We investigated effects of the stretching and the molecular orientation of aliphatic polyester fibers on the change of fine-structure. Glass transition temperature, molecular orientation and crystallinity increased according to the increase of stretching ratio.

• 기계저널
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• 제16권2호
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• pp.116-121
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• 1976

Non-steady hot wire method was adopted to measure thermal coductivity of paraffin wax in the phases of liquid and solid for the utilization of thermal energy storage. The instrument was tested with the measurement of thermal conductivity of water at various temperatures. The reproducibility of the instrumetn was found to be ${\pm}2%$, in which the results for water agree with the literature values. The thermal conductivity of paraffin wax varies from 0.177 W/m C to 0.236 W/m C when the phase changes from liquid to solid near the melting temperature.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2007년도 하계학술대회 논문집 Vol.8
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• pp.278-278
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• 2007

Ag conductive thick film has been used in bus and address electrodes of PDP (Plasma display panel). In PDP fabrication, the firing temperature of electrode is normally $550{\sim}580^{\circ}C$. For the application of PDP industry, we investigated an Ag conductive thick film with firing temperature. Low melting glass frit was used in the conductive thick film. The thermal properties of Ag and frit were determined by a hot stage microscopy. Based on the our results, we suggest that the Ag conductive thick film should be considered of the firing temperature which is correlated to the shrinkage, conductivity, and shape of thick film.

• 한국분말재료학회지
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• 제23권1호
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• pp.15-20
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• 2016

Niobium is one of the most important and rarest metals, and is used in the electronic and energy industries. However, it's extremely high melting point and oxygen affinity limits the manufacture of Nb coating materials. Here, a Nb coating material is manufactured using a kinetic spray process followed by hot isotactic pressing to improve its properties. OM (optical microscope), XRD (X-ray diffraction), SEM (scanning electron microscopy), and Vickers hardness and EPMA (electron probe micro analyzer) tests are employed to investigate the macroscopic properties of the manufactured Nb materials. The powder used to manufacture the material has angular-shaped particles with an average particle size of $23.8{\mu}m$. The porosity and hardness of the manufactured Nb material are 0.18% and 221 Hv, respectively. Additional HIP is applied to the manufactured Nb material for 4 h under an Ar atmosphere after which the porosity decreases to 0.08% and the hardness increases to 253 Hv. Phase analysis after the HIP shows the presence of only pure Nb. The study also discusses the possibility of using the manufactured Nb material as a sputtering target.