• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 1988년도 추계학술대회 논문집
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• pp.98-101
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• 1988

The material system (Bi$\sub$0.7/Pb$\sub$0.3/)Sr$_1$Ca$_1$Cu$\sub$1.8/Ox forms, at 845$^{\circ}C$, two major phases having a high Tc(100K) and a low Tc(∼70K) both of which consists of platelets and a non-superconducting minor phase which has rod-like shape and isolated by the major phases. As the sintering period increases, the amount of high Tc phase increases accompanying the decrease in low Tc phase while the amount of the non-superconducting phase is sintering period independent, resulting in a superconductor with Tc of 100K. Changes in compositions of each phase also occur during sintering due to evaporation of bismuth and lead.

• 한국재료학회지
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• 제30권2호
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• pp.61-67
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• 2020

BiFeO₃ with perovskite structure is a well-known material that has both ferroelectric and antiferromagnetic properties called multiferroics. However, leaky electrical properties and difficulty of controlling stoichiometry due to Bi volatility and difficulty of obtaining high relative density due to high dependency on the ceramic process are issues for BiFeO₃ applications. In this work we investigated the sintering behavior of samples with different stoichiometries and sintering conditions. To understand the optimum sintering conditions, nonstoichiometric Bi_1±xFeO_3±δ ceramics and Ti-doped Bi_1.03Fe_1-4x/3Ti_xO₃ ceramics were synthesized by a conventional solid-state route. Dense single phase BiFeO₃ ceramics were successfully fabricated using a two-step sintering and quenching process. The effects of Bi volatility on microstructure were determined by Bi-excess and Ti doping. Bi-excess increased grain size, and Ti doping increased sintering temperature and decreased grain size. It should be noted that Ti-doping suppressed Bi volatility and stabilized the BiFeO₃ phase.

• 한국분말재료학회지
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• 제23권4호
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• pp.263-269
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• 2016

Graphene oxide (GO) powder processed by Hummer's method is mixed with p-type $Bi_2Te_3$ based thermoelectric materials by a high-energy ball milling process. The synthesized GO-dispersed p-type $Bi_2Te_3$ composite powder has a composition of $Bi_{0.5}Sb_{1.5}Te_3$ (BSbT), and the powder is consolidated into composites with different contents of GO powder by using the spark plasma sintering (SPS) process. It is found that the addition of GO powder significantly decreases the thermal conductivity of the pure BSbT material through active phonon scattering at the newly formed interfaces. In addition, the electrical properties of the GO/BSbT composites are degraded by the addition of GO powder except in the case of the 0.1 wt% GO/BSbT composite. It is found that defects on the surface of GO powder hinder the electrical transport properties. As a result, the maximum thermoelectric performance (ZT value of 0.91) is achieved from the 0.1% GO/BSbT composite at 398 K. These results indicate that introducing GO powder into thermoelectric materials is a promising method to achieve enhanced thermoelectric performance due to the reduction in thermal conductivity.

• 한국전기전자재료학회논문지
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• 제34권5호
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• pp.386-392
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• 2021

Multiferroics exhibiting the coexistence and a possible coupling of ferromagnetic and ferroelectric order are attracting widespread interest in terms of academic interests and possible applications. However, room-temperature single-phase multiferroics with soft ferromagnetic and displacive ferroelectric properties are still rare owing to the contradiction in the origin of ferromagnetism and ferroelectricity. In this study, we demonstrated that sizable ferromagnetic properties are induced in the ferroelectric bismuth ferrite-barium titanate system simply by introducing Co ions into the A-site. It is noted that all modified compositions exhibit well-saturated magnetic hysteresis loops at room temperature. Especially, 70Bi_0.95Co_0.05FeO₃-30Ba_0.95Co_0.05TiO₃ manifests noticeable ferroelectric and ferromagnetic properties; the spontaneous polarization and the saturation magnetization are 42 µC/cm² and 3.6 emu/g, respectively. We expect that our methodology will be widely used in the development of perovskite-structured multiferroic oxides.

• 자원환경지질
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• 제35권3호
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• pp.179-189
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• 2002

중국 호남성 침주시에서 북동 16 km지점에 위치하는 시죽원 다금속 광상의 지질은 원생대의 변성퇴적암류, 데본기탄산염암, 쥬라기 화강암류, 백악기 반암류 및 초염기성맥암으로 구성된다. 시죽일 다금속 광상은 중-조립질 흑운모화강암과 관련되어 있다. 광체의 산출상태, 광물의 산출상태 및 공생관계를 토대로 광화시기는 스카른, 그라이젠 및 열수시기로 나뉜다. 스카른 시기의 광체는 주로 Ca-스카른으로 천리산 화강암체 주변에 발달되며, 석류석, 휘석, 베수비아나이트, 규회석, 각섬석, 형석, 녹염석, 방해석, 회중석, 철망간중석, 휘창연석, 휘수연석, 석석, 자연창연, 미확인 Bi-Te-S계 광물, 자철석 및 적철석 등이 산출된다. 그라이젠 시기는 중-조립질 흑운모화강암의 잔류용액과 관련되며, 광체는 판상 및 맥상으로 구분된다. 이 시기는 주로 석영, 장석, 백운모, 녹니석, 전기석, 황옥, 녹주석, 인회석, 회중석, 철망간중석, 휘수연석, 휘창연석, 석석, 자연창연, 미확인 우라늄광물, 미확인 희토류광물로 구성되고, 소량의 황철석, 자철석, 황동석, 적철석 등이 산출된다. 회중석은 누대조직을 보이며, 중심부에서 MoO$_3$ 함량이 9.17%로 외곽보다 높게 나타난다. 철망간중석의 화학조성은 WO$_3$; 71.20~77.37 wt.%, FeO; 9.37~18.4 wt.%, MnO; 8.17~15.31 wt.% 및 CaO; 0.01~4.82 wt.% 이다. 석석의 FeO 함량은 1.30~4.75 wt.%이고, 스카른 시기가 높은 함량을 보인다. 자연창연의 Te 및 Se 함량은 각각 0.00~1.06 wt.%와 0.00~0.57 wt.%이다. 미확인 Bi-Te-S 계 광물은 Bl: 78.62~80.75 wt.%, Te: 12.26~14.76 wt.%, Cu; 0.00~0.42 wt.%, S; 5.68~6.84 wt.%, Se; 0.44~0.78 wt.%.이다.

• Corrosion Science and Technology
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• 제7권6호
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• pp.370-374
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• 2008

In this study, we evaluated anti-corrosion properties of both commercial unleaded and lead epoxy primer for automotive substrate before applying to actual painting lines by salt spray test, and cyclic corrosion test, potentiodynamic test and electrochemical impedance spectroscopy. The difference in the corrosion resistance between automotive epoxy primers contained $Bi(OH)_{3}$ and leaded one was investigated. And it was also discussed the effect of zinc phosphate pretreatment to the epoxy primers. The specimen coated epoxy primer contained $Bi(OH)_{3}$ showed 0.5 V higher corrosion potential than that of bare steel. The result of salt spray test did not indicate remarkable difference of corrosion resistance in all specimens above $10{\mu}m$ thickness up to 1200 hours. In the cyclic corrosion test, epoxy primers contained $Bi(OH)_{3}$ on phosphated substrate performed good corrosion properties until 800 hours. The epoxy primer contained $Bi(OH)_{3}$ performed the equivalent corrosion resistance as leaded coating on phosphated steel, but slightly inferior to that of leaded on bare steel. These results show that the pre-treatment of zinc phosphate is effective as well as pigment changing in performing anti-corrosion properties in automotive bodies.

• Bulletin of the Korean Chemical Society
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• 제30권3호
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• pp.630-635
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• 2009

For use as a photocatalyst, bismuth tungsten oxide, $Bi_2WO_6$, was successfully synthesized by hydrothermal treatment at pH = 11 and heating at 200 ${^{\circ}C}$ for 24h, and samples were subsequently thermal treated at 400, 600, and 800 ${^{\circ}C}$ to increase crystallinity. TEM results revealed that the initial untreated particles were sheet‐shaped, grain size was below 80 nm, and it increased with treated temperatures. These $Bi_2WO_6$ samples absorbed at around 400 nm in the visible light range and the intensity of absorption was particularly strongest in samples thermal treated at 600 ${^{\circ}C}$. Their photoluminescence abilities, related to the recombination between the excited electrons and holes, were overall small for other general photocatalysts such as TiO2, and the smallest in the case of thermal treatment at 600 ${^{\circ}C}$, as reversible result of UV‐visible absorbance. Methyl orange of 5.0 ppm aqueous solution was almost completely removed after 2 h when treated over the $Bi_2WO_6$ thermal treated at 600 ${^{\circ}C}$.

• 반도체디스플레이기술학회지
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• 제22권1호
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• pp.64-71
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• 2023

In this study, we investigated the effects of BiAlSiO glass composition on its glass forming range, thermal properties, and plasma resistance. The results showed that increasing the Al2O3 content suppressed the tendency for crystallization and hindered glass formation beyond a certain threshold. Bi2O3 was found to increase the content of non-bridging oxygen, resulting in a decrease in glass transition temperature and an increase in thermal expansion coefficient. Furthermore, the etching rate was found to improve with increasing Al2O3 content but decrease with increasing SiO2 content. It was concluded that the boiling point of fluorinated compounds should be considered to 900℃. Therefore, this study is expected to contribute to the understanding of the properties of BiAlSiO glass and its application to low temperature melting PRG compositions.

• 마이크로전자및패키징학회지
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• 제17권2호
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• pp.49-54
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• 2010

n형 $Bi_2(Te,Se)_3$ 분말을 용해/분쇄법으로 제조하여 가압소결 후, 가압소결체의 열전특성을 $Bi_2(Te,Se)_3$ 잉곳과 비교하였으며, $Bi_2(Te,Se)_3$ 열전분말의 기계적 밀링처리가 가압소결체의 열전특성에 미치는 영향을 분석하였다. $Bi_2(Te,Se)_3$ 잉곳은 $24.2{\times}10^{-4}W/m-K^2$의 power factor를 나타내었으며, 이를 가압소결함으로써 power factor가 $27.3{\sim}32.3{\times}10^{-4}W/m-K^2$로 향상되었다. 기계적 밀링처리한 분말로 제조한 $Bi_2(Te,Se)_3$ 가압소결체는 $100^{\circ}C$에서 1.02의 무차원 성능지수를 나타내었으며, $130^{\circ}C$에서 외인성-내인성 천이거동을 나타내었다.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part2
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• pp.1223-1224
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• 2006

The p-type $(Bi_{0.2}Sb_{0.8})_2Te_3/(Pb_{0.7}Sn_{0.3})$Te functional gradient material (FGM) was fabricated by hot-pressing the mechanically alloyed $(Bi_{0.2}Sb_{0.8})_2Te_3$ and the 0.5 at% $Na_2Te-doped$ $(Pb_{0.7}Sn_{0.3})Te$ powders. Also, the n-type $Bi_2(Te_{0.9}Se_{0.1})_3/PbTe$ FGM was processed by hot-pressing the mechanically alloyed $Bi_2(Te_{0.9}Se_{0.1})_3$ and the 0.3 wt% Bi-doped PbTe powders. With ${\Delta}T$ larger than $300^{\circ}C$, the p-type $(Bi_{0.2}Sb_{0.8})_2Te_3/(Pb_{0.7}Sn_{0.3})Te$ FGM exhibited larger thermoelectric output power than those of the $(Bi_{0.2}Sb_{0.8})_2Te_3$ and the 0.5 at% $Na_2Te-doped$ $(Pb_{0.7}Sn_{0.3})Te$ alloys. For the n-type $Bi_2(Te_{0.9}Se_{0.1})_3/PbTe$ FGM, the thermoelectric output power superior to those of the $Bi_2(Te_{0.9}Se_{0.1})_3$ and the 0.3 wt% Bi-doped PbTe was predicted at ${\Delta}T$ larger than $300^{\circ}C$.