• 한국분말재료학회지
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• 제27권2호
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• pp.139-145
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• 2020

The powder manufacturing process using the gas atomizer process is easy for mass production, has a fine powder particle size, and has excellent mechanical properties compared to the existing casting process, so it can be applied to various industries such as automobiles, electronic devices, aviation, and 3D printers. In this study, a modified A4032-xSn (x = 0, 1, 3, 5, and 10 wt.%) alloy with low melting point properties is investigated. After maintaining an argon (Ar) gas atmosphere, the main crucible is tilted; containing molten metal at 1,000℃ by melting the master alloy at a high frequency, and Ar gas is sprayed at 10 bar gas pressure after the molten metal inflow to the tundish crucible, which is maintained at 800℃. The manufactured powder is measured using a particle size analyzer, and FESEM is used to observe the shape and surface of the alloy powder. DSC is performed to investigate the change in shape, according to the melting point and temperature change. The microstructure of added tin (Sn) was observed by heat treatment at 575℃ for 10 min. As the content of Sn increased, the volume fraction increased to 1.1, 3.1, 6.4, and 10.9%.

• 한국건설순환자원학회논문집
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• 제5권4호
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• pp.414-420
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• 2017

이 연구에서는 고온의 태양열 에너지를 저장하기 위한 고로슬래그 콘크리트의 열역학적 특성을 파악하였다. 고로슬래그 콘크리트의 열역학적 특성에 미치는 영향을 파악하기 위한 실험연구를 수행하였다. 실험변수로써 고로슬래그 함유량과 물-바인더 비를 고려하였다. 고로슬래그 콘크리트의 역학적 특성으로써 열사이클 전과 후의 압축강도 및 인장강도를 측정하고, 열적 특성으로써 열전도율과 비열을 측정하였다. 고로슬래그를 포함한 콘크리트의 열싸이클 적용 후의 잔류압축강도가 고로슬래그를 포함하지 않은 콘크리트의 잔류압축강도보다 크다. 또한, 고로슬래그를 혼입한 콘크리트의 열전도율이 고로슬래그를 포함하지 않은 콘크리트의 열전도율보다 더욱 크다. 이는 고로슬래그 콘크리트가 열에너지의 축열과 방열에 효과적인 것을 나타낸다. 실험연구 결과는 콘크리트 열저장 축열 모듈 설계에 효율적으로 활용될 수 있다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1996년도 하계학술대회 논문집 C
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• pp.1512-1515
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• 1996

Dense $SiC-ZrB_2$ electro-conductive ceramic composites were obtained by hot pressing for high temperature structural application. The influences of the $ZrB_2$ additions an the mechanical and electrical properties of $SiC-ZrB_2$ composites were investigated. Samples were prepared by adding 15, 30, 45 vol.% $ZrB_2$ particles as a second phase to a SiC matrix. Sintering of monolithic SiC and $SiC-ZrB_2$ composites were achieved by hot pressing under a $10^{-4}$ torr vacuum atmosphere from 1000 to $2000^{\circ}C$ with a pressure of 30 MPa and held for 60 minutes at $2000^{\circ}C$. SiC and $SiC-ZrB_2$ samples obtained by hot pressing were fully dense with the relative densities over 99%. Flexural strength and fracture toughness of the samples were improved with the $ZrB_2$ contents. In the case of SiC sample containing 30vol.% $ZrB_2$, the flexural strength and fracture toughness showed 45% and 60% increase, respectively compared to those of monolithic SiC sample. The electrical resistivities of $SiC-ZrB_2$ composites were measured utilizing the four-point probe method and they decreased significantly with Increasing $ZrB_2$ contents. The resistivity of SiC-30vol.% $ZrB_2$ showed $6.50{\times}10^{-4}{\Omega}{\cdot}cm$.

• 한국재료학회지
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• 제27권2호
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• pp.76-81
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• 2017

Recently, there have been many efforts to establish suitable processes for recycling fly ash, which is produced in thermal power plants and which poses serious environmental problems. Use of fly ash as a major ingredient of ceramic tiles can increase fly ash utilization, as well as reduce the cost of raw materials in ceramic tile production. In this study, the effects of fly ash addition on ceramic tile properties such as bending strength, water absorption and porosity were investigated. A manufacturing process of ceramic tile was developed for utilization of fly ash with high carbon content. In this approach, it is important to hold the ceramic tiles at a temperature that is sufficient for carbon oxidation, before the pores supplying oxygen to the inside of the ceramic tile are sealed. Ceramic wall tiles were manufactured with 0-40wt% of fly ash addition. The water absorption and porosity of the fired body were slightly changed with increasing fly ash content up to 30wt% and decreased with greater amounts of fly ash addition. The bending strength of ceramic tile including 10wt% fly ash increased, reaching a level comparable to that of ceramic tile without fly ash.

• 한국세라믹학회지
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• 제45권11호
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• pp.734-738
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• 2008

Ettringite$(3CaO{\cdot}Al_2O_3{\cdot}3CaSO_4{\cdot}32H_2O)$, one of the hydrated phase of Portland cement is usually formed in the early stage of hydration by the reaction of tricalciumaluminate$(C_3A)$ and gypsum. The rapid and strong crystal growth of separated rod-shaped ettringite have been utilized for the preparation of special cements of rapid setting, high strength and non-shrinking properties. The ettringite also has been noticed as a promising materials for the immobilization of various waste ions because of its unique crystal structure which has abundant channels and exchangeable ionic compounds. In this study, the formation and growth behavior of the ettringite was investigated in the system $C_3A-CaSO_4-H_2O$ using $C_3A$ clinker and gypsum to obtain a microporous body for waste ion immobilization. Ettringite was revealed to form by the dissolution-precipitation mechanism and the bulk body was by the entangled growth of rod-shaped ettringite crystals. The hardened body was composed of nearly pure rod-shaped ettringite interlocked each other with adequate mechanical strength. The homogeneity of structure, pore size, specific surface area and porosity of the hardened body were influenced by reaction temperature, water/powder ratio and the curing time. The hardened body prepared with water/powder ratio of 1 at $24^{\circ}C$ for one day showed excellent morphological properties for the purposed materials.

• 한국분말재료학회지
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• 제13권1호
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• pp.18-24
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• 2006

The brazing adhesion properties of Ag coated W-Ag electric contact on the Cu substrate have been investigated in therms of microstructure, phase equilibrium and adhesion strength. Precoating of Ag layer ($3{\mu}m$ in thickness) on the $W-40\%Ag$ contact material was done by electro-plating method. Subsequently the brazing treatment was conducted by inserting BCuP-5 filler metal (Ag-Cu-P alloy) layer between Ag coated W-Ag and Cu substrate and annealing at $710^{\circ}C$ in $H_2$ atmosphere. The optimum brazing temperature of $710^{\circ}C$ was semi-empirically calculated on the basis of the Cu atomic diffusion profile in Ag layer of commercial electric contact produced by the same brazing process. As a mechanical test of the electric contact after brazing treatment the adhesion strength between the electric contact and Cu substrate was measured using Instron. The microstructure and phase equilibrium study revealed that the sound interlayer structure was formed by relatively low brazing treatment at $710^{\circ}C$. Thin Ag electro-plated layer precoated on the electric contact ($3{\mu}m$ in thickness) is thought to be enough for high adhesion strength arid sound microstructure in interface layer.

• Journal of Electrical Engineering and Technology
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• 제13권2호
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• pp.918-927
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• 2018

Based on the actual operating environment of transformer, the aging tests of nitrile butadiene rubber (NBR) were conducted systematically under four conditions: in air, in transform oil, under compression in air and under compression in transform oil to studythe effect of high temperature, transform oil and compression stress simultaneously on the thermal aging behaviors of nitrile butadiene rubber and predict the lifetime. The effects of liquid media and compression stress simultaneously on the thermal aging behaviors of nitrile butadiene rubber were studied by using characterization methods such as IR spectrosc-opy, thermogravimetric measurements, Differential Scanning Calorimetry (DSC) measurements and mechanical property measurements. The changes in physical properties during the aging process were analyzed and compared. Different aging conditions yielded materials with different properties. Aging at $70^{\circ}C$ under compression stress in oil, the change in elongation at break was lower than that aging in oil, but larger than that aging under compression in air. The compression set or elongation at break as evaluation indexes, 50% as critical value, the lifetime of NBR at $25^{\circ}C$ was predicted and compared. When aging under compression in oil, the prediction lifetime was lower than in air and under compression in air, and in oil. It was clear that when predicting the service lifetime of NBR in oil sealing application, compression and media liquid should be involved simultaneously. Under compression in oil, compression set as the evaluation index, the prediction lifetime of NBR was shorter than that of elongation at break as the evaluation index. For the life prediction of NBR, we should take into account of the performance trends of NBR under actual operating conditions to select the appropriate evaluation index.

• 폴리머
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• 제33권1호
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• pp.91-95
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• 2009

폴리(아미드-이미드)와 연자성체의 블렌딩에 의해 고온에서 이용 가능한 내열성 전자기 노이즈 흡수용 필름을 제조하였다. N,N-디메틸아세트아미드에 폴리(아미드 아믹 산)을 용해시킨 후 연자성체 파우더를 혼합하고 이용액을 유리 기판에 캐스팅한 뒤 열을 가하여 이미드화하는 방법으로 전자기 노이즈 흡수 필름을 제조하였다. 제조된 필름의 열적 특성, 열 안정성 및 기계적 성질을 분석하고 마이크로 스트립 라인 법에 의해 전자기 흡수력을 측정하였는데,1 GHz에서 150 ${\mu}m$두께의 복합체 필름의 전력손실(power loss)은 약 25%였다.

• Metals and materials international
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• 제24권6호
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• pp.1213-1220
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• 2018

The effects of Cr and Fe addition on the mechanical properties of Ti-6Al-4V alloys prepared by direct energy deposition were investigated. As the Cr and Fe concentrations were increased from 0 to 2 mass%, the tensile strength increased because of the fine-grained equiaxed prior ${\beta}$ phase and martensite. An excellent combination of strength and ductility was obtained in these alloys. When the Cr and Fe concentrations were increased to 4 mass%, extremely fine-grained martensitic structures with poor ductility were obtained. In addition, Fe-added Ti-6Al-4V resulted in a partially melted Ti-6Al-4V powder because of the large difference between the melting temperatures of the Fe eutectic phase (Ti-33Fe) and the Ti-6Al-4V powder, which induced the formation of a thick liquid layer surrounding Ti-6Al-4V. The ductility of Fe-added Ti-6Al-4V was thus poorer than that of Cr-added Ti-6Al-4V.

• 콘크리트학회논문집
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• 제26권3호
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• pp.315-321
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• 2014

콘크리트는 경제적이면서 내구적인 건설재료로서 고단열성능을 가지고 있으므로 RC 구조물 뿐 아니라 내외장재에 많이 사용되고 있다. 또한 우수한 방사선 차폐 성능을 가지고 있으므로 원전구조물 및 플랜트 구조에 사용되고 있다. 그러나 이러한 고단열 성능으로 인해 내부에 원전구조물 내부에 화재나 멜트다운(melt-down)과 같은 문제가 발생하면 외부에서 인공적으로 온도를 낮출 방법이 매우 제한적이다. 이 연구는 자철광 골재와 철분말을 이용하여 고열전도 콘크리트를 제조하고 이에 대한 역학적 성능과 열전도 특성을 평가하였다. 자철광 골재를 체적비 최대 42.9%, 철분말을 1.5% 혼입하여 열전도 특성을 분석하였다. 자철광골재의 체적비가 30% 수준까지는 큰 열전도가 평가되지 않았으나, 이후 선형적으로 증가하여 체적비 42%가 되었을 때, 열전도는 2.5배 수준으로 증가하였다. 또한 철분말을 포함한 경우는 포함하지 않은 경우에 비해 열전도가 106~113% 증가하였다. 기존의 열전도 모델(ACI, DEMM, MEM)의 결과들이 실험 결과와 비교되었으며, 이러한 모델들은 자철광 및 철분말이 함유된 고열전도 콘크리트에 대해서도 합리적으로 적용될 수 있음을 검증하였다.