• 한국세라믹학회지
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• 제22권6호
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• pp.58-70
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• 1985

The bond strength of metal to ceramic sealing in Mo-Mn metallizing was investigated by examining the effects of flux composition in alumina ceramics particle size of molybdenum metal powder wet hydrogen atmosphere and temperature in metallizing. The maximum bond strength was obtained when the glass phase filled almost all the microstructural cavities around the interfacial area with few micropores. Such a favorable microstrcutre waas formed and maximum bond strength was observed between 130$0^{\circ}C$. Also the metal to ceramic bond strength was increased using finer molybdenum metal powder than coarse powder. When content of $SiO_2$ in the flux of alumina ceramics was constant metal to ceramic bond strength was improved with increasing the ratio of CaO to MgO in the flux.

• 한국세라믹학회지
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• 제44권3호
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• pp.152-156
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• 2007

Tungsten carbide powder was synthesized by SHS (self-propagating high-temperature synthesis). Except $WO_{3}$, each concentration of raw material ($WO_{3},\;Mg,\;NaCl,\;Na_{2}CO_{3},\;C$) was investigated. Final product was characterized by XRD and SEM. X-ray data demonstrated that the $NaCl+Na_{2}CO_{3}$ combined mixture has superiority in the WC formation process. Single phase and submicrometer WC powder was synthesized at the temperature below $1600^{\circ}C$. The role of sodium salts in combustion process was discussed, and chemical mechanism of WC formation was proposed. WC powder prepared by salt-assisted combustion synthesis has a size $0.2{\sim}3\;{\mu}m$ and low agglomeration degree.

• 한국분말재료학회지
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• 제15권2호
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• pp.142-147
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• 2008

The hypereutectic Al-20 wt%Si powders including some amount of Cu, Fe, Mg, Mn were prepared by a gas atomization process. In order to get highly densified Al-Si bulk specimens, the as-atomized and sieved powders were extruded at $500^{\circ}C$, Microstructure and tensile properties of the extruded Al-Si alloys were investigated in this study. Relative density of the extruded samples was over 98%. Ultimate tensile strength (UTS) in stress-strain curves of the extruded powders increased after T6 heat treatments. Elongation of the samples was also increased from 1.4% to 3.2%. The fracture surfaces of the tested pieces showed a fine microstructure and the average grain size was about $1{\mu}m$.

• 한국주조공학회지
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• 제31권3호
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• pp.145-151
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• 2011

Metallic foam has been known as a functional material which can be used for absorption properties of energy and sound. The unique characteristics of Al foam of mechanical, acoustic, thermal properties depend on density, cell size distribution and cell size, and these characteristics expected to apply industry field. Al-Zn-Mg-Cu alloy foams was fabricated by following process; firstly melting the Al alloy, thickening process of addition of Ca granule to increased of viscosity, foaming process of addition of titanium hydride powder to make the pores, holding in the furnace to form of cooling down to the room temperature. Metal foams with various porosity level were manufactured by change the foaming temperature. Compressive strength of the Al alloy foams was 2 times higher at 88% porosity and 1.2 times higher at 92% porosity than pure Al foams. It's sound and vibration absorption coefficient were higher than pure Al foams and with increasing porosity.

• Korean Chemical Engineering Research
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• 제60권2호
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• pp.229-236
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• 2022

동일 분체특성의 분진이 평균입경, 농도, 분진조건(부유 또는 퇴적) 변화에 따른 화재폭발 위험성을 조사하였다. 이를 위해 20L분진폭발시험장치, 열중량분석장치, 연소속도시험장치(UN시험법)를 사용하였다. 4종 분진(Sugar, Mg, Al, Zr)의 입경이 서로 다른 8개 분진 시료에 대하여 부유 분진의 폭발특성과 화염전파속도(FPV), 그리고 퇴적분진의 화염확산속도(FSV)를 조사하였다. 부유 분진 조건에서 Mg 및 Al 분진은 입경이 감소하면 폭발 위험성이 증가하였지만, Sugar는 입경 변화에 따른 폭발 위험성의 영향이 거의 나타나지 않았다. 부유 분진의 화염전파속도(FPV)는 마이크로 범위에서의 입경 변화보다 마이크로에서 나노로 입경이 감소하면 크게 증가하였다. 퇴적층의 화염확산속도(FSV)는 수평면(기울기 0°)보다 경사면(기울기 30°)에서 증가하는 경향을 나타냈으며, 경사면(기울기 30°) 퇴적층 조건에서는 상방 전파가 하방 전파보다 높게 나타났다.

• 한국초전도ㆍ저온공학회논문지
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• 제19권1호
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• pp.47-50
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• 2017

Carbon is proven to be very effective in pinning the magnetic vortices and improving the superconducting performance of $MgB_2$ at high fields. In this work, we have used polymethyl methacrylate (PMMA) polymer as a safe and cost effective carbon source. The effects of molecular weight of PMMA on crystal structure, microstructure as well as on superconducting properties of $MgB_2$ were studied. X-ray diffraction analysis revealed that there is a noticeable shift in (100) and (110) Bragg reflections towards higher angles, while no shift was observed in (002) reflections for $MgB_2$ doped with different molecular weights of PMMA. This indicates that carbon could be substituted in the boron honeycomb layers without affecting the interlayer interactions. As compared to undoped $MgB_2$, substantial enhancement in $J_c(H)$ properties was obtained for PMMA-doped $MgB_2$ samples both at 5 K and 20 K. The enhancement could be attributed to the effective carbon substitution for boron and the refinement of crystallite size by PMMA doping.

• 한국분말재료학회지
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• 제8권3호
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• pp.163-167
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• 2001

A bulk porous $CaZrO_3/MgO$ composite with plantinum nano-dispersion was synthesized in air atmosphere through the combination of several in situ reactions, including the pyrolysis of $PtO_2$. A mixture of $CaMg(CO_3)_2$(dolomite), $ZrO_2$, $PtO_2$ and LiF (0.5 wt%, as an additive) was cold isostatically pressed at 200 MPa and sintered at $1100^{\circ}C$ for 2 h. The porous $CaZrO_3/MgO/Pt$ composite ($CaZrO_3/MgO$ : Pt=99 : 1 in volume) had a uniformly open-porous structure (porosity: 56%) with three-dimensional (3-D) network and a narrow pore-size distribution, similarly to the porous $CaZrO_3/MgO$ composites reported before. Catalytic Properties (viz., NO direct decomposition and NO reduction by $C_2H_4$) of the $CaZrO_3/MgO/Pt$ composite were investigated up to $900^{\circ}C$. In the absence of oxygen, the NO conversion rate reached ~52% for the direct decomposition and ~100% for the reduction by $C_2H_4$, respectively. The results suggest the possibility of the porous composite as a multifunctional filter, i.e., simultaneous hot gas-filtering and $de-NO_x$ in one component.

• 농업과학연구
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• 제39권4호
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• pp.603-612
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• 2012

In this research, the feasibility of non-destructive measurement technique of pungency measurement was investigated for the red-pepper powders produced in different domestic areas in South Korea. The near-infrared absorption spectra in the range of 1100 nm~2300 nm was used to measure capsaicinoids content in red-pepper powders by using a NIR spectroscopy equipped with Acousto-optic tunable filters (AOTF). Fourth three different red-pepper powders from 14 different locations were collected and separated in three different particle size (below 0.425 mm, 0.425~0.71 mm, 0.71~1.4 mm) for the spectral measurements. The partial least square regression (PLSR) models to predict the capsaicinoids content depends on particle size were developed with the measured spectra. The determinant coefficients and standard errors of the developed models for the red-pepper powders of below 0.425 mm, 0.425~0.71 mm, and 0.71~1.4 mm were in the range of 0.859~0.887 and 12.90~12.99 mg/100 g, respectively. The PLS model with the pretreatment of Standard Normal Variate (SNV) for the red-pepper powders below 1.4 mm particle size showed the best performance with the determinant coefficient of 0.844 and the standard error of 14.63 mg/100 g.

• 한국수소및신에너지학회논문집
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• 제10권1호
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• pp.49-57
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• 1999

In order to study the effect of high energy ball milling on the $Mg_2Ni+Ni$, $Mg_2Ni+0.5Ni+0.5Al$ powders, we have investigated on the discharge properties, microstructures. The powder size of samples decreased as ball milling time. From the XRD results, the crystal structure of $Mg_2Ni+Ni$ mixed powders were changed to amorphous or nano-structure after 60hr ball milling. The discharge capacities of both $Mg_2Ni+Ni$ and $Mg_2Ni+0.5Ni+0.5Al$ powders increased, with increasing ballmilling time, the maximum capacity(342mAh/g) was shown for the 60 hrs ballmilled $Mg_2Ni+Ni$ sample. The capacity decreased drastically after a few charge-discharge cycles.

• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2014년도 추계학술대회 논문집
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• pp.45-45
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• 2014

The importance of magnesium alloys has significantly increased due to their low density, high strength/weight ratio, very good electromagnetic shielding features and good recyclability. However, unfortunately, Mg alloys are very susceptible to corrosion due to their high chemically activities (= -2.356 V vs. NHE at $25^{\circ}C$), hence, most commercial Mg alloys require corrosion protective coatings. Organic coating such as painting, powder coating and electrophoretic deposition of paint (E-paint) is typically used in the final stages of the coating process of Mg alloys. In this study, effect of pre-immersion time on the deposition of E-paint on AZ31 Mg alloy was investigated. It was found that during pre-immersion time, AZ31 Mg alloy rapidly reacts with E-paint solution and paint can be self-deposited on the AZ31 surface without applying of electric current. The pore size on the E-painted AZ31 Mg alloy increased with increasing pre-immersion time from 0 to 5 min. Both adhesion and corrosion resistance of E-painted AZ31 Mg alloy decreased with increasing pre-immersion time. The best E-paint AZ31 Mg alloy, which showed stronger adhesion after water immersion test and good corrosion resistance, was started to deposit after 5 s of pre-immersion time.