• 한국세라믹학회지
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• 제55권6호
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• pp.527-555
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• 2018

High-temperature thermal insulation materials challenge extensive oxide candidates such as porus $SiO_2$, $Al_2O_3$, yttria-stabilized zirconia, and mullite, due to the needs of good mechanical, thermal, and chemical reliabilities at high temperatures simultaneously. Recently, porous rare earth (RE) silicates have been revealed to be excellent thermal insulators in harsh environments. These materials display attractive properties, including high porosity, moderately high compressive strength, low processing shrinkage (near-net-shaping), and very low thermal conductivity. The current critical challenge is to balance the excellent thermal insulation property (extremely high porosity) with their good mechanical properties, especially at high temperatures. Herein, we review the recent developments in processing techniques to achieve extremely high porosity and multiscale strengthening strategy, including solid solution strengthening and fiber reinforcement methods, for enhancing the mechanical properties of porous RE silicate ceramics. Highly porous RE silicates are highlighted as emerging high-temperature thermal insulators for extreme environments.

• 한국분말재료학회지
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• 제19권6호
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• pp.435-441
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• 2012

A new manufacturing process of Fe-Cr-Al powder porous metal was attempted. First, ultra-fine fecralloy powders were produced by using the submerged electric wire explosion process. Evenly distributed colloid (0.05~0.5% powders) was dispersed on PU (Polyurethane) foam through the electrospray process. And then degreasing and sintering processes were conduced. In order to examine the effect of sintering temperature in process, pre-samples were sintered for two hours at temperatures of $1350^{\circ}C$, $1400^{\circ}C$, $1450^{\circ}C$, and $1500^{\circ}C$, respectively, in $H_2$ atmospheres. A 24-hour TGA (thermo gravimetric analysis) test was conducted at $1000^{\circ}C$ in a 79% $N_2$+21% $O_2$ to investigate the high temperature oxidation behavior of powder porous metal. The results of the high temperature oxidation tests showed that oxidation resistance increased with increasing sintering temperature (2.57% oxidation weight gain at $1500^{\circ}C$ sintered specimen). The high temperature oxidation mechanism of newly manufactured Fe-Cr-Al powder porous metal was also discussed.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part 1
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• pp.594-595
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• 2006

Porous bearings are lubricated the oil that is contained in porous metal. Then they are always used with no oil supply, because of that, widely used electric motors. But, if oil flow out less than the limit, troubles often happen. This report shows that attempt of estimating oil quantity in porous bearing by using calculation that based Reynols' equation and Darcy's law, aimed of developing long life bearing. And comparing with experimental and calculation result, we show possibility of estimating rest oil quantity in porous bearing at steadry state by calculation.

• 한국진공학회지
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• 제15권5호
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• pp.518-526
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• 2006

나노 다공성 알루미나 박막을 제작하고 이를 주형으로 사용해서 진공증착에 의해 규칙적으로 배열된 나노우물구조와 나노그물구조의 금속 박막들(알루미늄, 주석, 코발트)을 제작하였다. 원하는 금속물질을 증발시키기 위하여 저항가열 방법을 사용하였으며, 증착은 torr의 기저진공 속에서 수행되었다. 실험결과에 의하면, 나노우물과 나노그물 구조의 박막 중 어떤 구조가 합성되느냐 하는 것은 증착되는 물질의 양에 의해서 큰 영향을 받는다는 사실을 알 수 있었다. 세포의 크기가 100 nm이고 세공 직경이 60 nm인 다공성 알루미나 박막을 사용했을 때는 대략 우물구조를 합성하는데 필요한 질량의 절반이하 정도가 증착되게 되면 그물 구조가 합성되는 경향을 보여주었다.

• Tribology and Lubricants
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• 제1권1호
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• pp.88-101
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• 1985

함유베어링의 성능특징과 다공율사이에는 어떤 관계가 있다. 그 관계를 뚜렷하게 하기 위하여 이 논문에서는 수치해석과 실험을 통하여 그 관계를 규명하였다. 수치해석과 실험결과는 잘 일치되며 다공율의 증가에 따라 姿勢角과 마찰인자가 증가하는데 다공율의 증가에 따라 負荷容量은 감소한다는 것을 보여 주고 있다.

• 한국재료학회지
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• 제16권8호
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• pp.503-510
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• 2006

The measurement of specific gases is based on the reversible conductivity change of sensing materials in semiconductor type gas sensors. For an application as gas sensors of high sensitivity, porous $SnO_2$ films have been fabricated by anodizing of pure Sn foil in oxalic acid and characteristics of anodic tin oxide films have been investigated. Pore diameter and distribution were dependent on process conditions such as electrolyte concentration, applied voltage, anodizing temperature, and time. Characteristics of anodic films were explained with current density-time curves.

• Advances in nano research
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• 제5권4호
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• pp.393-414
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• 2017

Forced vibration behavior of porous metal foam nanoplates on elastic medium is studied via a 4-variable plate theory. Different porosity distributions called uniform, symmetric and asymmetric are considered. Nonlocal strain gradient theory (NSGT) containing two scale parameters is employed for size-dependent modeling of porous nanoplates. The present plate theory satisfies the shear deformation effect and it has lower field variables compared with first order plate theory. Hamilton's principle is employed to derive the governing equations. Obtained results from Galerkin's method are verified with those provided in the literature. The effects of nonlocal parameter, strain gradient, foundation parameters, dynamic loading, porosity distributions and porosity coefficient on dynamic deflection and resonance frequencies of metal foam nanoscale plates are examined.

• 공업화학
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• 제3권1호
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• pp.156-171
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• 1992

Chitin was isolated from crab shell. Chitosan, which was prepared by the deacetylation of chitin, was acylated to obtain N-acetyl(regenerated chitin), N-propionyl, N-butyryl, N-hexanoyl, N-decanoyl and N-maleated chitosans and their metal ion adsorption characteristics of N-acylchitosans were investigated. In order to enhance the adsorptivity, their porous beads were prepared and their adsorptivity with respect to the porosity and the adsorptivities for metal ions($Cu^{2+}$, $Ni^{2+}$, $CO^{2+}$, $Mn^{2+}$, $Ag^{+}$)were investigated. Their metal ion adsorptivities were remarkably imporved compared to those of chitin. As the larger acyl groups were introduced, adsorptivity increased, but that of N-decanoyl chitosan showed some decrease because of steric hindrance of the bulky N-decanoyl group. N-Maleated chitosan containing carboxyl group showed highly improved adsorptivity, and N-acylchitosans showed the good selective adsorption in the mixed metal ions($Cu^{2+}$, $Ni^{2+}$, $CO^{2+}$, $Mn^{2+}$ and $Ag^{+}$). They also showed excellent adsorption characteristics as chelating polymers.

• 한국주조공학회지
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• 제23권5호
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• pp.244-250
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• 2003

The aim of this study is fabricating of composite filler metal (CFM) by a combination of selective laser sintering (SLS) of stainless steel powders (RapidSteel $2.0^{TM}$ and liquid phase infiltration of Ag-28 wt.%Cu alloy. Porous stainless steel body with inter-connected pore channels was fabricated by SLS, binder decomposing and densification processes. By the direct contact infiltration, the narrow inter-particle channels of the porous body were completely filled with the Ag-28 wt.%Cu alloy infiltrant. During infiltration, the dissolved elements of Fe, Ni and Cr from the porous body were solved into copper solid solution phases, which consist of eutectic structure of composite metal matrix. The S10C/CFM/S10C joints, which have narrow clearance gaps between them up to 10 micrometers, were joined successfully by self-feeding of filler metal from the matrix of CFM. The CFM kept its original thickness and microstructure after brazing. The tensile strength of brazed specimen was higher than 30 kgf/$mm^2$ and showed a typical ductile fracture mode in the CFM.

• 한국생산제조학회지
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• 제21권6호
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• pp.855-859
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• 2012

Silicon nanowires (SiNWs) were fabricated by a metal-assisted chemical etching of Si and the porous structure on their surfaces was controlled by changing the volume ratio of the etching solution composed of hydrofluoric acid, hydrogen peroxide, and deionized water. The concentration of hydrogen peroxide as the oxidant was varied for controlling the porosity of SiNWs. The optical properties of porous SiNWs were unique and very different from those of single-crystalline Si, as characterized by measuring their photoluminescence and Raman spectra for different porosities.