• 한국주조공학회지
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• 제36권5호
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• pp.153-158
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• 2016

The lost foam casting process was used to fabricate Al-Si-Mg cast specimens, and the effects of the chemical composition and process variables on the tensile properties and the mold filling ability were investigated. Some porosity formation was observed in thick sections of the casting and better tensile properties were obtained for thin sections, presumably because of their lower porosity and the higher cooling rate. Tensile properties were not clearly enhanced by grain refining treatment with Ti; however, the elongation was significantly improved by Sr modification of the Al-Si-Mg alloy. The mold filling distance was generally proportional to the pouring temperature of the melt, and the distance was also increased by the addition of Ti.

• Bulletin of the Korean Chemical Society
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• 제17권7호
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• pp.621-625
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• 1996

A variety of metal oxides were coated by sol-gel process from their metal alkoxides on the ribbons of Co-based and Fe-based amorphous alloys, and the effects of surface oxide coating on the magnetic properties of the alloy are investigated. The core loss is found to be reduced significantly by the oxide coating, the loss reduction becoming more prominent at higher frequencies. The shape of the hystersis loop is also dependent upon the kind of the coated metal oxide. The coatings of MgO, SiO2, MgO·SiO2 and MgO·Al2O3 induce tensile stress into the Fe-based ribbon whereas those of BaO, Al2O3, CaO·Al2O3, SrO·Al2O3 and BaO·Al2O3 induce compressive stress. These results may be explained by the modification of domain structures via magnetoelastic interactions with the shrinkage stress induced by the sol-gel coating.

• 접착 및 계면
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• 제17권3호
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• pp.110-116
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• 2016

야간 우천시 수막에 의한 차선의 재귀반사 효율 감소로 운전자의 시인성이 저하되고 있으며 이로 인해 많은 사고가 발생한다. 시인성을 높이기 위해 메틸메타크릴레이트의 현탁중합 시 소수성으로 표면이 개질된 $SrAl_2O_4:Eu^{2+}$,$Dy^{3+}$ 축광 물질을 도입하고 이를 캡슐화하였다. 표면 개질에 사용된 물질과 라디칼 개시제의 종류, 사용된 축광 물질의 양, 그리고 캡슐의 입도가 캡슐 내부의 축광 물질 함량($W_{TGA}$)에 미치는 영향을 TGA를 사용하여 분석하였다. 그 결과 축광 물질의 함량은 7~81 wt%까지 넓은 분포를 나타내었으며, 이러한 결과는 현탁중합이 넓은 함량 범위의 축광 물질을 캡슐화하는데 적합한 것을 의미한다. 축광 물질의 함량이 낮은 경우에는 캡슐의 입도가 감소함에 따라 $W_{TGA}$이 증가하였으나, 축광 물질의 함량이 높을 때에는 캡슐의 입도에 별 영향을 받지 않았다. 축광 캡슐 중 지름 $425{\sim}710{\mu}m$의 축광 캡슐을 활용하여 형광 차선 시편을 제작하였으며 LED램프를 20 min 동안 조사한 후 광원을 제거하였을 때, 100 s 동안 약 $300mcd/m^2$ 이상의 휘도를 유지했다. 이러한 결과로 미루어 보아 제조된 축광 캡슐은 차선 위의 유리 비드를 대체하기에 충분한 가능성을 가짐을 알 수 있었다.

• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2018년도 춘계학술대회 논문집
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• pp.74-74
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• 2018

Ti-6Al-4V alloys have been widely used as orthopedic materials because of their excellent corrosion resistance and mechanical properties. However, it does not bind directly to the bone, so it requires a surface modification. This problem can be solved by nanotube and micropore formation. Plasma electrolytic oxidation (PEO) treatment for micropore, which combines high-voltage spark and electrochemical oxidation, is a new way of forming a ceramic coating on light metals such as titanium and its alloys. This method has excellent reproducibility and can easily control the shape and size of the Ti alloy. In this study, formation of bioactive surface by PEO-treatment after $2^{nd}$ ATO technique of Ti-6Al-4V alloy was invesgated by various instrument. Nanotube oxide surface structure was formed on the surface by anodic oxidation treatment in 0.8 wt.% NaF and 1M $H_3PO_4$ electrolytes. After nanotube formation, nanotube layer was removed by ultrasonic cleaning. PEO-treatment was carried out at 280V for 3 minutes in the electrolytic solution containing the bioactive substance (Mg, Zn, Mn, Sr, and Si). The surface of Ti-6Al-4V alloy was observed by field emission scanning electron microscopy (FE-SEM, S-4800 Hitachi, Japan). An energy dispersive X-ray spectrometer (EDS, Inca program, Oxford, UK) was used to analyze the spectra of physiologically active Si, Mn, Mg, Zn, and Sr ions. The PEO film formed on the Ti-6Al-4V alloy surface was characterized using an X-ray diffractometer (TF-XRD, X'pert Philips, Netherlands). It is confirmed that bioactive ions play an essential role in the normal bone growth and metabolism of the human skeletal tissues.

• 한국세라믹학회지
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• 제44권11호
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• pp.613-617
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• 2007

The variations of physical and dielectric properties of low temperature dielectrics based on typical aluminoborosilicate glasses modified with several divalent oxides were investigated. The divalent oxides studied here included CaO, MgO, BaO, SrO and ZnO. All samples containing either 35 wt% or 45 wt% alumina filler were prepared at the same processing condition and then fired at $850^{\circ}C$ for 30 min. The resultant characteristics of fired samples depended on the choice of the divalent ion and the content of the alumina filler. Except for the ZnO modification, all other samples containing 35 wt% filler demonstrated promising densification as they exhibited reasonably high densities of 3.07-3.31 $g/cm^3$ and high shrinkages of 14.0-16.4%. Particularly, the sample containing ZnO was distinguished with large variations compared to the base sample, which can be highlighted with earlier densification and crystallization at unexpectedly low temperatures. The negative effects of the ZnO modification on densification and dielectric properties were thought to be associated with earlier crystallization potentially by influencing effective densification via viscous flow. As an optimum composition, the sample containing only CaO showed the most promising characteristics such as $k{\sim}8.05$ and $tan{\delta}{\sim}0.0018$ when 35 wt% alumina filler was used.

• 한국세라믹학회지
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• 제40권6호
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• pp.594-600
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• 2003

산소분자를 선택적으로 투과.분리할 수 있는 L $a_{0.7}$S $r_{0.3}$G $a_{0.6}$F $e_{0.4}$ $O_{3-}$$\delta$/ 페롭스카이트계 혼합전도성 산소투과 분리막을 제조하였으며, 소결조건에 따라 발현되는 미세구조적 특징을 고찰하였다. He/air 분위기하에서 분리막의 산소투과 유속에 미치는 분리막의 두께 및 표면개질의 영향을 평가하여 속도결정단계에 대하여 논의하였다. 미세구조가 조절된 분리막에 대하여 산소투과유속을 측정함으로써, 입계분율의 증가에 따라 산소투과에 대한 저항이 증가함을 알 수 있었다. 분리막을 통하여 선택적으로 투과된 산소를 이용하여 메탄의 부분산화반응에 의한 합성가스를 생성하였으며, 메탄의 전환율 및 합성가스의 수율을 측정.평가하였다. 기체의 혼합비 및 반응온도의 변화를 통해 합성가스 생성의 적정조건을 선택할 수 있었으며, 600시간의 장기 안정성 시험을 통해, L $a_{0.7}$S $r_{0.3}$G $a_{0.6}$F $e_{0.4}$ $O_{3-}$$\delta$/ 계 산소투과 분리막이 고온의 극심한 환원분위기하에서 안정적으로 사용이 가능한 것으로 판단하였다.

• 한국전기전자재료학회논문지
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• 제34권1호
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• pp.1-7
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• 2021

This study investigated the structural, dielectric, ferroelectric, and strain properties of (0.98-x)Bi1/2Na1/2TiO3-0.02BiFeO3-xSrTiO3 (BNT-BF-100xST, x＝0.20, 0.22, 0.24, 0.26, and 0.28). All samples were successfully synthesized using the conventional solid-state reaction method and sintered at 1,175℃ for 2 h. The average grain size of the BNT-BF-100x ceramics decreased with increasing ST content. Furthermore, we observed that the ferroelectric- relaxor transition temperature (TF-R) decreased with increasing ST content, which eventually vanished in the BNT-BF-24ST ceramics. The results indicated that a ferroelectric to relaxor phase transition could be induced by ST modification. Consequently, a large electromechanical strain of 633 pm/V at 4 kV/mm was observed for the BNT-BF-26ST ceramics. These results imply that our materials have the competitive advantage of larger strain under lower operating field conditions compared with other BNT-based lead-free piezoelectric ceramics. We expect that BNT-BF-ST lead-free piezoelectric ceramics are promising candidates as a novel ternary BNT-based system and can find potential applications in actuators.

• 한국연소학회:학술대회논문집
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• 한국연소학회 2004년도 제28회 KOSCO SYMPOSIUM 논문집
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• pp.37-41
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• 2004

Quenching phenomena is one of major concern in development of millimeter or sub-millimeter scale micro combustor for the size of the combustor is near extinction condition. In this work we focused on the effect of combustor wall condition that was parameterized by Perovskite LSC($La_{0.8}$$Sr_{0.2}$$CoO_3$) redox catalyst. The experiment was done by variable gap-width 2D wall equipment. The flame was produced by premixed methane-air jet issuing from millimeter-scale slot burner and it propagated through the narrow gap of the walls. By comparison of flame behaviour near catalyst-coated wall and simple glass wall, we investigated the effect of possible surface reaction on quenching phenomena. The flame between two plates was observed where the gap of the plates was reduced stepwise from 20mm to a distance of quenching occurrence. The two flames with and without surface modification were almost same by observation. But the gap for the occurrence of quenching was increased between catalyst-coated wall. So we concluded that surface reaction close to combustor wall has a negative effect on micro combustion.

• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2009년도 춘계학술대회 논문집
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• pp.100-100
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• 2009

$TiO_2$ is widely being used as a semiconductor electrode for DSSC. Anti-recombination property and surface area of $TiO_2$ give an important influence to the DSSC efficiency. In this study, $TiO_2$ electrode was fabricated on FTO using screen printing method. Various overlayers were coated on them by dip coating in solution of saturated $Ba(NO_3)_2$, $Mg(NO_3)_2$ and $N_{2}O_{6}Sr$. They reduced the recombination of electrons from photo excited state of Ru dye. The atmospheric plasma treatment was applied to both the $TiO_2$ and each overlayer coated $TiO_2$ surfaces to improve contact ability with dye. We prepared four samples, one sample has bare $TiO_2$ surfaces to improve contact ability with dye. We prepared four samples, one sample has bare $TiO_2$ electrode and the other samples consist of each overlayer coated $TiO_2$ electrodes. We used XRD, FE-SEM, J-V, IPCE and EIS in order to investigate characteristic.

• 대한방사선기술학회지:방사선기술과학
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• 제38권3호
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• pp.305-313
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• 2015

2011년 일본 후쿠시마 원전 사고 이후 국내외에서 관련 연구 및 관리체제 정비가 이루어지고 있다. 국내에서도 물의 방사능 오염에 대한 우려가 높아졌으며, 이에 따라 환경부를 중심으로 물 속 방사성 물질 관리체제 정비가 이루어지고 있다. 본 연구에서는 원전 사고의 피해 당사국이며 인접국가인 일본의 관리체제 정비 현황을 분석하였다. 분석한 결과 일본에서는 법제 정비 후 문부과학성이 방사능 측정의 이론적인 내용을 규정하고, 환경성은 실제 공공수역 및 지하수의 수질 오염 상황을 감시하며, 지방자치단체 등 관련된 일선 기관에서 물 환경의 방사능 오염 상황을 모니터링하고 있다. 지역별로 보면 지방측정소들은 전 국토 대상의 조사를 분담하며, 원자력 시설 주변에서 별도의 모니터링을 하고 있으며, 원전 사고 이후 후쿠시마 인근 지역에 대한 모니터링이 추가로 운영 중이다. 기준치 중 음료수 및 수도수의 관리 목표치는 10 Bq/kg이며, 후쿠시마 주변 공공수역과 지하수는 1 Bq/L로 되어 있다. 측정 주기는 매 시간에서 연 1회까지 다양하며 검사에 따라 정기적 또는 부정기적으로 실시되고 있다. 주된 측정 항목에는 공간선량률, 전${\alpha}$, 전${\beta}$, ${\gamma}$핵종, Cs-134, Cs-137, Sr-89, Sr-90, I-131 등이 있다. 이에 비해 우리나라는 원자력시설 주변과 먹는 물에 대한 규제기준은 정비되어 있는 반면, 일반적인 공공수역에 대한 관리는 2014년에 시작되었다. 따라서 향후 WHO 등의 가이드라인을 참고하여 국내 체계를 보완할 것으로 예상된다. 일본의 관리 체계는 우리나라의 일반적인 공공수역 방사성물질 기준을 확립할 때 참고가 될 수 있다고 사료된다.