• 한국세라믹학회지
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• 제46권6호
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• pp.609-614
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• 2009

The low-temperature preparation of porous ceramics was carried out using mixtures of alumina-zinc borosilicate (ZBS) glass. The compositions of alumina-ZBS glass mixture with PMMA pore-former were unfortunately densified. Because PMMA was evaporated below the softening point of ZBS glass ($588{^{\circ}C}$), the densification through the pore-filling caused by the capillary force might occur. Howerver, those with carbon possessed pores where carbon was evaporated above the softening point. The porous ceramic having 35% porosity was successively fabricated by the low-temperature sintering process below $900{^{\circ}C}$ using 45 vol% of alumina, 45 vol% ZBS of glass, and 10 vol% of carbon as starting materials.

• 한국세라믹학회지
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• 제52권2호
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• pp.128-132
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• 2015

In this study, we prepared cadmium phosphate glasses with various compositions, given by $xCdO-(100-x)P_2O_5$ (x = 10-55 mol%), and analyzed their Fourier transform infrared spectra, dissolution rate, thermal expansion coefficient, glass transition temperature, glass softening temperature, and optical band gap. We found that the thermal expansion coefficient and dissolution rate increased while the glass transition temperature and glass softening temperature decreased with increasing CdO content. These results suggest that CdO acts as a network modifier in binary phosphate glass and weakens its structure.

• 한국재료학회:학술대회논문집
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• 한국재료학회 2005년도 춘계학술발표대회 및 제8회 신소재 심포지엄 논문개요집
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• pp.176-176
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• 2005

• 한국자원식물학회지
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• 제8권2호
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• pp.183-188
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• 1995

땅두릅 여룹철 연화재배(軟化栽培) 가능성(可能性)을 검토(檢討)하기 위하여 흑색(黑色) PE와 은색(銀色) 단섬유불직포(短纖維不織布)를 이용하여 5월 정식(定植)을 포함하여 6월, 7월, 8월 정식기(定植期)에 대하여 시험(試驗)한 결과(結果)는 다음과 같다. 1. 수확소요일수(收穫所要日數)는 5월 정식(定植)에서 20일(日)이고 7월, 8월 정식(定植)에서는 15일로 단축(短縮)되었으나 생육기간중(生育期間中)의 적산온도(積算溫度)는 $400^{\circ}C$ 범위이었다. 2. 7월 정식(定植)에서 땅두릅 연화수(軟化莖)의 수량(收量)은 고온(高溫)으로 인한 연부현상(軟腐現狀)으로 낮은 경향(傾向)이었다. 3. 각(各) 부위별(部位別) 경도(硬度)는 상위부(上位部)가 연(軟)하고 하위부(下位部)가 단단한 경향(傾向)이고, 저온저장(低溫貯藏) 7일후(日後)에도 신선도(新鮮度)는 유지(維持) 되었다. 4. 5월, 6월 정식재배시(定植栽培時) 18,000천원/ha 이상(以上)의 소득(所得)을 얻을 수 있었다.

• 공업화학
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• 제24권4호
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• pp.402-406
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• 2013

본 연구에서는 납사 크래킹 잔사유로부터 용융전기방사용 핏치가 열처리 개질 방법에 의하여 제조되었다. 개질된 핏치의 연화점과 물성은 질소유량, 열처리 온도 및 반응시간 같은 개질 조건에 따라 영향을 받았다. 이중에서 열처리온도가 핏치의 분자량 분포 및 연화점에 큰 영향력을 미쳤다. 열처리 온도가 증가함에 따라서 표면 작용기들의 분해와 고리화 반응으로 C/H 몰비와 평균분자량이 증가하였다. 또한, 벤젠 불용분(BI)과 퀴놀린 불용분(QI)값이 감소되었고, 분자량 분포의 폭이 더 좁아지는 것으로 보여주었다. 연화점이 $155^{\circ}C$인 개질 핏치로부터 용융전기방사법을 이용하여 $4.8{\mu}m$의 직경을 갖는 탄소섬유를 얻을 수 있었다. 용융전기방사법이 저섬경화 섬유를 제조하는데 기존의 용융방사법보다 더 용이할 것으로 여겨진다.

• 한국재료학회지
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• 제23권5호
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• pp.276-280
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• 2013

Coal tar is the primary feedstock of premium graphitizable carbon precursor. Coal tars are residues formed as byproducts of thermal treatments of coal. Coal tar pitches were prepared through two different heat treatment schedules and their properties were characterized. One was prepared with argon and oxidation treatment with oxygen; the other was prepared with oxygen treatment at low temperature and then argon treatment at high temperature; both used coal tar to prepare coal tar pitches. To modulate the properties, different heat treatment temperatures ($300{\sim}400^{\circ}C$) were used for the coal tar pitches. The prepared coal tar pitches were investigated to determine several properties, such as softening point, C/H ratio, coke yield, and aromaticity index. The coal tar pitches were subject to considerable changes in chemical composition that arose due to polymerization after heat treatment. Coal tar pitch showed considerable increases in softening point, C/H ratio, coke yields, and aromaticity index compared to those characteristics for coal tar. The contents of gamma resin, which consists of low molecular weight compounds in the pitches and is insoluble in toluene, showed that the degree of polymerization in the pitches was proportional to C/H ratio. Using an oxidizing atmosphere like air to prepare the pitches from coal tar was an effective way to increase the aromaticity index at relatively low temperature.

• 열처리공학회지
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• 제18권1호
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• pp.18-23
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• 2005

Effect of cold rolling on microstructural changes has been investigated for a Zn-15%Al alloy to elucidate the reason for its work softening behavior. Fully annealed microstructure of the Zn-15%Al alloy is characterized by ${\eta}$ grains and (${\eta}+{\alpha}$) lamellar colonies, where ${\eta}$ and ${\alpha}$ are Zn-rich HCP and Al-rich FCC phases, respectively. The hardness decreases continuously with increasing cold rolling degree, exhibiting work softening behavior. It is revealed that during the cold rolling, (${\eta}+{\alpha}$) lamellar colonies gradually change into equiaxed ${\eta}$ and ${\alpha}$ grains due to dynamic recrystallization at room temperature, while pre-existing ${\eta}$ grains are only deformed without recrystallization. Furthermore, cold rolling causes the precipitation of dissolved Al solutes in ${\eta}$ grains. In view of these results, change of (${\eta}+{\alpha}$) phases from lamellar to equiaxed morphology, which results in structural softness and increase in equiaxed ${\eta}/{\alpha}$ grain boundaries with higher mobility, and deterioration of solution hardening by precipitation of Al solutes from ${\eta}$ grains, are thought to contribute to the work softening of Zn-15%Al alloy.

• 한국식품과학회지
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• 제29권4호
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• pp.758-763
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• 1997

당도와 ascorbic acid함량이 높은 우수한 신선 과일인 생대추를 장기간 저장하기 위하여 숙도 및 저장온도에 따른 무등품종 대추의 호흡특성, 저장 중 품질변화를 측정하였다. 녹숙 대추와 적숙 대추의 숙도에 따라서 호흡속도는 차이가 없어서 non-climacteric특성으로 간주될 수 있었고, 호흡의 온도의존성에서도 숙도간에 차이가 없었다. 적숙 대추가 녹숙 대추에 비해서 단위과중이 약간 크며, 가용성 고형분 농도와 ascorbic acid 함량이 약간 높았다. 대추는 저장 중 조직의 연화가 먼저 나타난 후 부패가 진행되었다. 대추의 저장 중 연화 및 부패의 진행은 녹숙대추의 경우가 적숙대추에 비해서 늦어서 장기저장을 위해서는 녹숙대추를 저장하는 것이 유리하였다. 저장 중 녹숙 대추의 표면색택은 붉은 색으로 착색이 진행되고 가용성 고형분은 증가하고, 총산과 ascorbic acid 함량은 감소하였다. $-2^{\circ}C,\;0^{\circ}C,\;5^{\circ}C,\;10^{\circ}C,\;20^{\circ}C$에서의 녹숙 대추의 저장실험에서는 $-2^{\circ}C$에서는 저온장해가 발생하였고, $5^{\circ}C$ 이상의 온도에서는 온도가 높을수록 품질변화와 부패가 빨라서, $0^{\circ}C$가 저장적온으로 판단되었다. 저장적온인 $0^{\circ}C$에서 대추는 40일정도 밖에 신선한 상태로 저장될 수 없어서 보다 장기간의 저장이 가능한 포장 기법의 적용이 필요한 것으로 평가되었다.

• 한국세라믹학회지
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• 제46권3호
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• pp.313-316
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• 2009

A zinc borosilicate glass having a low softening temperature of $490^{\circ}C$ has been investigated as a protective layer for Ag patterns against chemical reactions with a $I^-/I_3^-$ electrolyte in dye-sensitized solar cells (DSSCs). A thick glass layer was prepared by the typical screen printing and firing processes to obtain a final thickness of ${\sim}5{\mu}m$. The chemical leaching performance of the glass layer in the electrolyte revealed that the reactive Ag pattern can be significantly protected by utilizing the low softening protective layer. The electrical resistance of the FTO-coated glass substrate was effectively maintained at a low value of ${\sim}27{\Omega}$ as long as the glass layer was well densified at a sufficiently high temperature of ${\sim}520^{\circ}C$. The transmittance of the layer was near 60%, depending on the firing temperature of the glass layer.

• Journal of Advanced Marine Engineering and Technology
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• 제33권2호
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• pp.322-329
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• 2009

Machinability of LAM(Laser Assisted Machining) has been studied for ceramics such as $Al_2O_3$, $Si_3_N4$ and $ZrO_2$ by $CO_2$ laser. It was possible to remove ceramics by PCBN tool because material became softening and deterioration by local laser beam irradiation. The advantage of LAM is the ability to produce larger material removal rates and tool life. But, for cutting of $Al_2O_3$ and $ZrO_2$, stage of laser power control was needed owing to thermal shock with high temperature of workpiece by laser power. And when $Si_3N_4$ was machined by LAM, $N_2$ gas spouted from surface of one cause of high temperature. Characteristics of LAM were analyzed using pyrometer, dynamometer, SEM and EDS to measure temperature of workpiece surface, cutting force, variation of machining surface and structure of lattice respectively. As the result of this study, it was found that machinability of LAM for ceramics in $CO_2$ laser and mechanism of LAM was different according to the kind of ceramics because of properties of materials.