• 한국재료학회지
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• 제25권1호
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• pp.27-31
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• 2015

This paper proposes a novel way of fabricating aligned porous Sn by freeze-drying of camphene slurry with stannic oxide ($SnO_2$) coated Sn powders. The $SnO_2$ coated Sn powders were prepared by surface oxidation of the initial and ball-milled Sn powders, as well as heat treatment of tin chloride coated Cu powders. Camphene slurries with 10 vol% solid powders were prepared by mixing at $50^{\circ}C$ with a small amount of oligomeric polyester dispersant. Freezing the slurry was done in a Teflon cylinder attached to a copper bottom plate cooled at $-25^{\circ}C$. Improved dispersion stability of camphene slurry and the homogeneous frozen body was achieved using the oxidized Sn powder at $670^{\circ}C$ in air after ball milling. The porous Sn specimen, prepared by freeze-drying of the camphene slurry with oxidized Sn powder from the heat-treated Sn/tin chloride mixture and sintering at $1100^{\circ}C$ for 1 h in a hydrogen atmosphere, showed large pores of about $200{\mu}m$, which were aligned parallel to the camphene growth direction, and small pores in their internal walls. However, $100{\mu}m$ spherical particles were observed in the bottom part of the specimen due to the melting of the Sn powder during sintering of the green compact.

• 한국표면공학회지
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• 제49권3호
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• pp.260-264
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• 2016

In this study, fractured surface morphology and mechanical properties of Ni-Cr-Mo alloys with various contents of Mo for dental material use have been evaluated by mechanical test. The alloys used were Ni-13Cr-xMo alloys with Mo contents of 4, 6, 8, and 10 wt.%, prepared by using a vacuum arc-melting furnace. Ni-13Cr-xMo alloys were used for mechanical test without heat treatment. The phase and microstructure of alloys using an X-ray diffraction (XRD) and optical microscopy (OM) were evaluated. To examine the mechanical properties of alloys according to microstructure changes, the tensile test and the hardness test were carried out using tensile tester. To understand the mechanism of Mo addition to Ni-Cr alloy on mechanical property, the morphology and fractured surfaces of alloys were investigated by field-emission scanning electron microscope (FE-SEM). As a result, 79Ni-13Cr-8Mo alloy was verified that the tensile strength and the hardness were better than others. Varying Mo content, the changes of microstructures of alloys were identified by OM and SEM and that of 79Ni-13Cr-8Mo alloy was proved fabricated well. Microstructures of alloys were changed depending on Mo content ratio. It has been observed that 8% alloy had the most suitable mechanical property for dental alloy.

• 한국재료학회지
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• 제22권7호
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• pp.368-373
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• 2012

Glasses were prepared with compositions of $(13-x)BaO-80B2_O_3-7Li_2O{\cdot}xSm_2O_3$, BBLSx(x=0.5, 0.4, 0.3) by melting the starting materials of boron oxide(99.9%), lithium oxide(99.9%), barium carbon oxide(99.9%), and samarium oxide(99.9%) and then quenching the melt at $1350^{\circ}C$. This led to good-quality BBLSx(x=0.4, 0.3) and poor-quality BBLSx(x=0.5) glasses. The physical and structural properties of the BBLSx glasses were studied by means x-ray diffraction, scanning electron microscopy(SEM), differential scanning calorimetry(DSC), and dielectric spectroscopy. From the x-ray diffraction and SEM results, the quality of the BBLSx glasses significantly depends on the $Sm_2O_3$ concentration. The x-ray diffraction pattern showed that the crystallites in the BBLSx glasses after heat treatment at $700^{\circ}C$ may be $LiBaB_9O_{15}$. From the DSC results, the glass transition temperatures($T_g$), crystallization temperatures($T_c$), and the maximum temperatures of the crystallized($T_p$) BBLSx glasses all changed with the $Sm_2O_3$ concentration. According to the dielectric spectroscopy results, the values of the real dielectric constant and Tan ${\delta}$ of the BBLSx glasses depended on the $Sm_2O_3$ concentration. The values of the real dielectric constant and Tan ${\delta}$ were also shown to depend on the measuring temperature, possibly due to the ion migration in the bulk of the BBLSx glasses.

• 대한치과보철학회지
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• 제59권4호
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• pp.442-450
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• 2021

컴퓨터 지원 설계 및 제조 기법(CAD-CAM)은 치과 영역에서 급속도로 발전해온 분야로, 다양한 보철 치료 영역에 적용되고 있다. 이 중 절삭형 방식(Subtractive Manufacturing)으로 분류되는 절삭가공 기법을 이용한 의치 제작은 상용화된 디지털 총의치 제작 방식 중 하나이며, 동시에 첨가형 방식(Additive Manufacturing)으로 분류되는 레이저 소결 혹은 용융 기법을 활용하여 피개의치를 위한 금속구조물을 보다 효율적으로 제작할 수 있게 되었다. 본 증례에서는, CAD-CAM을 통해 절삭형 방식으로 제작한 상악 총의치와 3D 금속 프린팅을 이용한 금속구조물과 절삭형 방식으로 제작된 인공치를 접목한 하악 임플란트 피개의치를 제작하였다. 이를 통해 기능적, 심미적으로 적절한 임상적 결과를 얻었으므로 이를 보고하는 바이다.

• 한국재료학회지
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• 제29권3호
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• pp.167-174
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• 2019

To improve the performance of carbon nanofibers as electrode material in electrical double-layer capacitors (EDLCs), we prepare three types of samples with different pore control by electrospinning. The speciments display different surface structures, melting behavior, and electrochemical performance according to the process. Carbon nanofibers with two complex treatment processes show improved performance over the other samples. The mesoporous carbon nanofibers (sample C), which have the optimal conditions, have a high sepecific surface area of $696m^2g^{-1}$, a high average pore diameter of 6.28 nm, and a high mesopore volume ratio of 87.1%. In addition, the electrochemical properties have a high specific capacitance of $110.1F\;g^{-1}$ at a current density of $0.1A\;g^{-1}$ and an excellent cycling stability of 84.8% after 3,000 cycles at a current density of $0.1A\;g^{-1}$. Thus, we explain the improved electrochemical performance by the higher reaction area due to an increased surface area and a faster diffusion path due to the increased volume fraction of the mesopores. Consequently, the mesoporous carbon nanofibers are demonstrated to be a very promising material for use as electrode materials of high-performance EDLCs.

• Tribology and Lubricants
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• 제34권6호
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• pp.270-278
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• 2018

STS 316L prepared by additive manufacturing (AM) exhibits deterioration of mechanical properties and wear resistance due to the presence of defects such as black-of-fusion defects, internal porosity, residual stress, and anisotropy. In addition, high surface roughness (integrity) of AM products remains an issue. This study aimed to apply ultrasonic nanocrystal surface modification (UNSM) technology to STS 316L prepared by AM to increase the surface hardness, to reduce the surface roughness, and to improve the friction and wear behavior to the level achieved by bulk material manufactured using traditional processes. Herein, the as-received and polished specimens were treated by UNSM technology and their resulting properties were compared and discussed. The results showed that UNSM technology increased the surface hardness and reduced the surface roughness of the as-received and polished specimens. These results can be attributed to grain size refinement and pore elimination from the surface. Moreover, the friction of the as-received and polished specimens after UNSM technology was lower compared to those of the as-received and polished specimens, but no significant differences in wear resistance were found.

• 한국재료학회지
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• 제31권3호
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• pp.156-161
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• 2021

Cr-Si based alloys are not only excellent in corrosion resistance at high temperatures, but also have good wear resistance due to the formation of Cr3Si phase, therefore they are promising as metallic coating materials. Aluminum is often added to Cr-Si alloys to improve the oxidation resistance through which stable alumina surface film is formed. On the other hand, due to the addition of aluminum, various Al-containing phases may be formed and may negatively affect the heat resistance of the Cr-Si-Al alloys, so detailed investigation is required. In this study, two Cr-Si-Al alloys (high-Si & high-Al) were prepared in the form of cast ingots through a vacuum arc melting process and the microstructural changes after high temperature heating process were investigated. In the case of the cast high-Si alloy, a considerable amount of Cr3Si phase was formed, and its hardness was significantly higher than that of the cast high-Al alloy. Also, Al-rich phases (with the high Al/Cr ratio) were not found much compared to the high-Al alloy. Meanwhile, it was observed that the amount of the Al-rich phases reduced by the annealing heat treatment for both alloys. In the case of the high temperature heating at 1,400 ℃, no significant microstructural change was observed in the high Si alloy, but a little more coarse and segregated AlCr phases were found in the high Al alloy compared to the cast state.

• Journal of Animal Science and Technology
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• 제55권5호
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• pp.451-460
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• 2013

본 연구는 참깻묵이 거세 한우의 비육성적과 등심의 지방산 조성, 유리 아미노산 함량 및 관능평가에 미치는 영향을 조사 하고자 실시되었다. 평균 체중 412.08 kg의 거세한우 12두를 체중과 월령을 고려하여 대조구 (참깻묵 무급여구)와 시험구 (14.6개월령부터 참깻묵 급여구)로 배치한 후, 480일간 사양 시험을 실시하였다. 대조구와 시험구의 종료 시 체중, 총증체량 및 일당증체량은 각각 741.17과 762.67 kg, 331.84와 347.84 kg 및 0.69와 0.72 kg 나타났으며, 사료요구율은 대조구와 시험구가 각각 15.31, 14.87 kg으로 참깻묵 급여구인 시험구가 3% 더 낮게 나타났다. 대조구와 시험구의 냉도체중과 근내지방도는 각각 424.17과 447.00 kg, 4.83 및 5.50으로 나타났으나, 통계적인 유의성은 없었다. 처리구별 1등급 이상 출현율은 시험구가 83.3%로 대조구 66.7%에 비하여 높았다. 도체 등심의 융점은 대조구가 $30.65^{\circ}C$, 시험구가 $28.28^{\circ}C$로 시험구에서 유의적으로 (p<0.05) 낮았다. 처리구별 등심 내 지방산 조성 중 포화지방산인 $C_{14:0}$ (myristic acid)과 $C_{16:0}$ (palmitic acid)의 함량은 시험구가 유의적 (p<0.05)으로 낮았고, 불포화지방산인 $C_{18:1}$ (oleic acid)은 시험구가 유의적 (p<0.05)으로 높았다. 등심 내 유리 아미노산 조성 중 소고기의 맛과 관련된 특징적인 유리 아미노산인 glutamic acid의 함량은 시험구가 대조구에 비하여 유의적 (p<0.05)으로 높았다. 관능평가 요인 중 연도와 종합기호도에서도 시험구가 유의적 (p<0.05)으로 높은 점수를 받았다. 이상과 같은 결과를 종합 해 보면 거세 한우에 참깻묵 급여는 육질등급 출현율 개선 뿐 아니라 소고기 맛과 건강에 유익한 불포화지방산 함량을 증가시키는데 긍정적인 영향을 미치는 것으로 판단된다.

• Composites Research
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• 제30권2호
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• pp.116-125
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• 2017

본 연구의 목적은 고온 산화성 분위기하에서 기계적물성이 우수한 탄화규소섬유(SiC Fiber)를 파일롯-규모로의 생산 제조공정을 개발하는 것이다. 프리세라믹 전구체로서 폴리카보실란(PCS)을 사용하여 탄화규소섬유를 제조하였다. 연속성의 PCS 섬유는 $300{\sim}350^{\circ}C$에서 PCS를 용융한 후에 용융방사로부터 얻었다. 열처리 전에 섬유의 불융화를 위하여 공기 분위기하에서 경화를하였다. 경화 전, 후에 측정한 FT-IR 스펙트라 피크로 부터 경화도를 계산하였다. 탄화규소섬유의 물성은 경화도에 따라 크게 영향을 받았다. 본 개발에서 열처리 중 섬유의 장력 조절로 우수한 물성을 갖는 탄화규소섬유를 얻었다. 탄화규소섬유의 화학조성과 기계적물성은 안정화섬유의 열처리시의 이송속도에 영향을 받았다. 탄화규소섬유를 공기분위기하 $1000^{\circ}C$에서 1분부터 50시간까지 노출한 후에 인장시험을 수행하였다. 그 결과 인장강도는 약 60%까지 감소함을 보여주었다. 장시간 노출시험시 낮은 인장 강도값을 나타내는 섬유는 화학성분 분석시 섬유의 표면에 많은 탄소량을 함유하고 있었다.

• 한국환경농학회지
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• 제13권3호
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• pp.271-278
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• 1994

Maleic anhydride와 4-chloroaniline에 의한 amination 반응(反應)을 통하여 CPMA를 회수(回收)하고, 다시 acetic anhydride 및 sodium acetate에 의한 CPMA의 dehydration 반응(反應)을 거쳐 CPMI를 합성(合成)하였다. 생성물(生成物)의 녹는점(CPMA $200-202^{\circ}C$, CPMI $116-118^{\circ}C$) 비교(比較)와 NMR 분석(分析)을 통하여 화합물의 순도(純度)(95% 이상)를 결정(決定)하였다. 생육(生育) 초기단계(初期段階)의 수수에서 metolachlor에 의한 생육억제(生育抑制)는 근부(根部)에 비하여 지상부(地上部)에서 더욱 크게 나타났으며, 이러한 지상부(地上部)의 생육저해(生育沮害)는 종자(種子)에 CPMI를 피복처리(被覆處理)한 경우에 뚜렷한 감소(減少)를 보였다. CPMI를 수수 종자(種子) 1kg당 1.2g의 수준(水準)으로 종자(種子)에 피복처리(被覆處理)한 경우에 가장 높은 약해경감(藥害輕減) 활성(活性)을 나타내었으며, 지상부(地上部)의 50% 생육억제(生育抑制)를 나타내는 metolachlor의 농도(濃度)($GR_{50}$치(値))로 표시한 약해경감지수(藥害輕減指數)는 무처리종자(無處理種子)($15\;{\mu}M$)에 비하여 피복처리(被覆處理) 종자(種子) ($53\;{\mu}M$) 에서 약 3배 정도 증대(增大)되었다. CPMI의 처리(處理) 여부에 관계없이 [$^{14}C$]metolachlor의 흡수(吸收)에는 차이(差異)가 인정(認定)되지 않았다. CPMI를 피복처리(被覆處理)한 수수에서 metolachlor의 부활성화(不活性化)가 촉진되어 수수내의 흡수(吸收)된 metolachlor의 대부분이 빠른 시간내에 glutathione과의 결합(結合)을 통하여 대사(代謝) 또는 해독(解毒)되었다.