• 한국주조공학회지
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• 제42권2호
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• pp.77-82
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• 2022

일방향응고 초내열합금 CM247LC의 응고조건에 따른 조직과 기계적 특성을 고찰하기 위해 초기 응고조건을 인위적으로 변화시켜 일방향응고를 진행하였다. 초기 응고 조건은 알루미나 판의 삽입, 접종재의 삽입, Ni foil의 삽입과 냉각판에 직접 주입 등으로 조절하였으며, 이에 따라 초기 결정립의 수의 많은 차이를 보였으며 응고방향과 평행으로 성장하는 결정립의 형태 및 γ' 석출상의 크기 등에서도 많은 차이를 보였다. 냉각속도가 빠른 용탕의 냉각판에 직접 주입한 경우 많은 결정립, 미세한 γ'상 및 γ-γ'공정상 등이 나타났다. 빠른 냉각은 고체/액체 사이의 온도구배를 증가시켜 일방향응고 후 1차 수지상 간격을 미세하게 함으로써 우수한 인장특성을 갖게 하였다.

• 한국분말재료학회지
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• 제30권6호
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• pp.509-515
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• 2023

Lead-free perovskite ceramics, which have excellent energy storage capabilities, are attracting attention owing to their high power density and rapid charge-discharge speed. Given that the energy-storage properties of perovskite ceramic capacitors are significantly improved by doping with various elements, modifying their chemical compositions is a fundamental strategy. This study investigated the effect of Zn doping on the microstructure and energy storage performance of potassium sodium niobate (KNN)-based ceramics. Two types of powders and their corresponding ceramics with compositions of (1-x)(K,Na)NbO₃-xBi(Ni_2/3Ta_1/3)O₃ (KNN-BNT) and (1-x)(K,Na)NbO₃-xBi(Ni_1/3Zn_1/3Ta_1/3)O₃ (KNN-BNZT) were prepared via solid-state reactions. The results indicate that Zn doping retards grain growth, resulting in smaller grain sizes in Zn-doped KNN-BNZT than in KNN-BNT ceramics. Moreover, the Zn-doped KNN-BNZT ceramics exhibited superior energy storage density and efficiency across all x values. Notably, 0.9KNN-0.1BNZT ceramics demonstrate an energy storage density and efficiency of 0.24 J/cm³ and 96%, respectively. These ceramics also exhibited excellent temperature and frequency stability. This study provides valuable insights into the design of KNN-based ceramic capacitors with enhanced energy storage capabilities through doping strategies.

• 한국작물학회지
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• 제31권1호
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• pp.97-103
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• 1986

파종기를 달리하였을 때 보리의 주요생태 및 수량구성형질에 대한 지역간 변이를 검토하기 위하여 올보리를 공시품종으로 1982~84 3개년 동안 수원, 대전 및 진주에서 시험을 수행한 바 그 결과를 요약하면 다음과 같다. 1. 출아일수의 년차간 변이는 적기내 파종에서는1~5일인데 비하여 적기 이후는 7~14일로 파종기가 늦어짐에 따라 변이폭이 컸는데 대체로 일평균 온도가 15$^{\circ}C$ 전후에서 7일이면 출아하였다. 2. 최고분얼기는 파종기에 따라 차이가 커서 조파의 경우 3월 20일 인데 비하여 만기파종은 5월 1일 경에 왔으며 유효분얼한계기는 파종후 대전은 104~144일, 진주 135-142일 이었고, 유효경비율은 지역 및 파종기에 따라 37~77%로 남부지역일수록 높았다. 3. 유수는 초기에는 완만한 신장을 하다가 영화분화이후는 지역에 따라 1.05~l.95mm일의 빠른 속도로 신장을 하였으며, 절간의 신장시기는 대전에 비하여 수원은 5~7일이 늦은 반면 진주는 6일 정도가 빨랐다. 4. 수량구성요소중 지역간에는 일수입수만이 유의성을 보였으나 파종기에 따라서는 모든 요소가 유의성을 나타내어 지역간 차이보다도 파종기가 더 크게 지배하고 있음을 알 수 있었다. 5. 수량은 지역간에는 유의성은 인정되지 않았으나 지역별 파종기에 따른 감소율은 북부지역에서 컸다.

• 한국재료학회지
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• 제28권6호
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• pp.343-348
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• 2018

Recently, the properties of nanostructured materials as advanced engineering materials have received great attention. These properties include fracture toughness and a high degree of hardness. To hinder grain growth during sintering, it is necessary to fabricate nanostructured materials. In this respect, a high-frequency induction-heated sintering method has been presented as an effective technique for making nanostructured materials at a lower temperature in a very short heating period. Nanopowders of W and $Al_2O_3$ are synthesized from $WO_3$ and Al powders during high-energy ball milling. Highly dense nanostructured $W-Al_2O_3$ composites are made within three minutes by high-frequency induction-heated sintering method and materials are evaluated in terms of hardness, fracture toughness, and microstructure. The hardness and fracture toughness of the composite are $1364kg/mm^2$ and $7.1MPa{\cdot}m^{1/2}$, respectively. Fracture toughness of nanostructured $W-Al_2O_3$ is higher than that of monolithic $Al_2O_3$. The hardness of this composite is higher than that of monolithic W.

• Journal of Welding and Joining
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• 제18권3호
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• pp.83-88
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• 2000

Laser cladding processing allows rapid transfer of heat to the material being processed with minimum conduction into base metal, resulting in low total heat input. The effects of Nd:YAG laser cladding with wire feeding on the mechanical properties of Inconel alloy were investigated. inconel alloy is used as the material of nuclear steam generator tubing because of its mechanical properties and corrosion resistance properties. The device for Nd:YAG laser cladding with wire feeding was designed. It consists of the wire feeding system, the wire cladding system and the shielding gas system which prevents the clad layer from being oxidized. Experimental as results indicated that the wire feeding direction and position were important for laser cladding with wire feeding. The wire feeding speed should be adapted according to cladding speed for good shaping of clad layer. The effect of heat on the HAZ size can be limited and the growth of grain size of HAZ size was not serious. The hardness of clad layer and heat affected zone increased with increasing of cladding speed.

• Journal of Plant Biotechnology
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• 제40권4호
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• pp.185-191
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• 2013

Over the past decades, carbon dioxide concentration of the atmosphere of the world has increased significantly, and thereby the greenhouse effect has become a social issue. To solve this problem, new renewable energy sources including solar, hydrogen, geothermal, wind and bio-energy are suggested as alternatives. Among these new energy sources, bio-energy crops are widely introduced and under rapid progress. For example, corn and oilseed rape plants are used for the production of bio-ethanol and bio-diesel, respectively. However, grain prices has increased severely because of the use of corn for bio-ethanol production. Therefore, non-edible switchgrass draws attention as an alternative source for bio-ethanol production in USA. This review describes the shortage of fossil energy and an importance of switchgrass as a bio-energy crop. Also, some characteristics of its major cultivars are introduced including growth habit, total output of biomass yields. Furthermore, biotechnological approaches have been conducted to improve the productivity of switchgrass using tissue culture and genetic transformation.

• 한국세라믹학회지
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• 제49권1호
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• pp.118-123
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• 2012

GDC20($Ce_{0.8}Gd_{0.2}O_{1.9}$) powder was synthesized from Ce and Gd nitrate solutions using ammonium carbonate($(NH_4)_2CO_3$) as a precipitant. Attrition-milling of the powder, which had been calcined at $700^{\circ}C$ for 4 h, decreased an average particle size of 2.2 ${\mu}m$ to 0.5 ${\mu}m$. The milled powder consisted of nano-sized spherical primary particles. Due to the excellent sinterability of the powder, sintering of the powder compacts for 4 h showed relative densities of 80% at 1000 $^{\circ}C$ and 96.5% at $1200^{\circ}C$, respectively. Densification was found to almost complete at $1300^{\circ}C$, resulting in a dense and homogeneous microstructure with a relative density of 99.5%. The grains of ~0.2 ${\mu}m$ in size at $1200^{\circ}C$ grew to ~1 ${\mu}m$ in size at $1300^{\circ}C$ as a result of a rapid grain growth.

• 한국식품영양과학회지
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• 제30권2호
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• pp.250-255
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• 2001

Effect of molding temperature on the quality changes of extruded meju was studied. Meju was molded at 8$0^{\circ}C$, 6$0^{\circ}C$ and 4$0^{\circ}C$, and then stored at $25^{\circ}C$ with 50% of relative humidity for 30 days. The texture of the cooked soybean grain showed that the firmness and cohesiveness were increased, and consistency was decreased by decrease of molding temperature. The density of the meju molded at 8$0^{\circ}C$, 6$0^{\circ}C$ and 4$0^{\circ}C$ were 1.072g/mL, 1.079g/mL and 1.203g/mL, respectively. The meju molded at 4$0^{\circ}C$ had significantly higher density than those molded at 8$0^{\circ}C$ or 6$0^{\circ}C$. Also, delay of water evaporation, acidification, and rapid growth of fungal mycellium were observed on the sample with molding temperature at 4$0^{\circ}C$ during fermentation. Activity of amylase and protease, contents of total reducing sugar and amino nitrogen of 4$0^{\circ}C$-molded meju were represented lower level than those of 6$0^{\circ}C$ or 8$0^{\circ}C$-molded sample. Therefore, it was considered that the molding temperature was an important factor for meju fermentation and molding temperature of 6$0^{\circ}C$ or over would be acceptable.

• 한국전기전자재료학회논문지
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• 제36권3호
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• pp.286-291
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• 2023

Perovskite materials are promising candidates for next-generation optoelectronic devices owing to their outstanding external quantum efficiency, high color purity, and ability to tune the light emission wavelength. However, conventional thermal annealing processes caused the degradation of perovskite, resulting in poor optoelectronic properties and a short lifetime. Herein, we propose a laser-induced recrystallization of perovskite thin film to enhance its light-emitting properties. Laser-induced recrystallization process was performed using rapid and instantaneous laser heating, which successfully induced grain growth of the perovskite material. The laser processing conditions were thoroughly optimized based on theoretical calculations and various material analyses such as x-ray diffraction, scanning electron microscope, and photoluminescence spectroscopy.

• 한국재료학회지
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• 제24권9호
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• pp.495-501
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• 2014

Despite having many attractive properties, $ZrO_2$ ceramic has a low fracture toughness which limits its wide application. One of the most obvious tactics to improve its mechanical properties has been to add a reinforcing agent to formulate a nanostructured composite material. Nanopowders of $ZrO_2$ and Cr were synthesized from $CrO_3$ and Zr powder by high energy ball milling for 10 h. Dense nanocrystalline $2/3Cr-ZrO_2$ composite was consolidated by a high-frequency induction heated sintering method within 5 min at $600^{\circ}C$ from mechanically synthesized powder. The method was found to enable not only rapid densification but also the inhibition of grain growth, preserving the nano-scale microstructure. Highly dense $2/3Cr-ZrO_2$ composite with relative density of up to 99.5% was produced under simultaneous application of a 1 GPa pressure and the induced current. The hardness and fracture toughness of the composite were 534 kg/mm2 and $7MPa{\cdot}m1/2$, respectively. The composite was determined to have good biocompatibility.