• 한국분말재료학회지
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• 제13권5호
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• pp.360-365
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• 2006

The phase stability of tetragonal phase in Y-TZP was investigated in terms of the distribution of grain sizes and heat-treating atmosphere. Y-TZP with various grain sizes were prepared using duration time at $1600^{\circ}C$ as experimental parameter. Accumulated grain size distributions were built from the SEM micrographs and the amount of tetragonal phase were measured using XRD. Both results were compared to determine the critical grain size before and after heat-treatment in vacuum. The critical grain size drastically decreased compared with the small increase of average grain size due to the autocatalytic effect which critically affects the tetragonal to monoclinic phase transformation. After heat-treatment in reductive atmosphere critical grain size relatively increased due to the stabilization of tetragonal phase. The formation of oxygen vacancies during heat-treatment was ascribed to the increase of stability.

• 한국결정성장학회지
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• 제9권4호
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• pp.360-364
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• 1999

The growth of crystals with high melting point$t_{fus}$$\geq$$1600^{\circ}C$ faces the researcher with experimental problems, as the choice of materials that withstand such high t is rather limited. Many metallic construction materials are in this high t range already molten or exhibit at least a drastically reduced mechanical strength. The very few materials with$t_{fus}$$1600^{\circ}C$ as e.g. W, Mo, and partially even Ir are more or less sensitive against oxygen upon heating. Whenever possible, high t crystal growth is performed under inert atmosphere (noble gases). Unfortunately, many oxides are not thermodynamically stable under such conditions, as reduction takes place within such atmosphere. A thoroughly search for suitable growth conditions has to be performed, that are on the one side "oxidative enough" to keep the oxides stable and on the other side "reductive enough" to avoid destruction of constructive parts of the crystal growth assembly. The relevant parameters are t and the oxygen partial pressure${po}_{2}$. The paper discusses quantitatively relevant properties of interesting oxides and construction materials and wasy to forecast theri behavior under growth conditions.

• 한국결정성장학회:학술대회논문집
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• 한국결정성장학회 1999년도 PROCEEDINGS OF 99 INTERNATIONAL CONFERENCE OF THE KACG AND 6TH KOREA·JAPAN EMG SYMPOSIUM (ELECTRONIC MATERIALS GROWTH SYMPOSIUM), HANYANG UNIVERSITY, SEOUL, 06월 09일 JUNE 1999
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• pp.51-67
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• 1999

The growth of crystals with high melting points tfus$\geq$1$600^{\circ}C$ faces the researcher with experimental problems, as the choice of materials that withstand such high t is rather limited. Many metallic construction materials are in this high t range already molten or exhibit at least a drastically reduced mechanical strength. The very few materials with tfus》1$600^{\circ}C$ as e.g. W, Mo, and partially even Ir are more or less sensitive against oxygen upon heating. Whenever possible, high t crystal growth is performed under inert atmosphere (noble gases). Unfortunately, any oxides are not thermodynamically stable under such conditions, as reduction takes place within such atmosphere. A thoroughly search for suitable growth conditions has to be performed, that are on the one side "oxidative enough" to keep the oxides stable and on the other side "reductive enough" to avoid destruction of constructive parts of the crystal growth assembly. The relevant parameters are t and the oxygen partial pressure pO2. The paper discusses quantitatively relevant properties of interesting oxides and construction materials and ways to forecast their behavior under growth conditions.r growth conditions.

• 대한화학회지
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• 제23권2호
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• pp.99-103
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• 1979

세개의 ${\alpha}$,${\beta}$-불포화알데히드, 신남알데히드, 크로톤알데히드, 아크로레인을 여러가지 일차 아민 존재하에서 테트라카르보닐철산염으로 환원시켜 상당히 다른 수득률로 N-알킬아민을 합성하였다. 보통, $KHFe(CO)_4$ (22mmole)와 일차아민(22∼44mmole)과 ${\alpha}$,${\beta}$-불포화 알데히드 (22mmole)를 에탄올 용매에 넣고 일산화탄소 분위기하에 실온에서 9∼60시간 자석 젓개로 저어주면 일산화탄소를 천천히 흡수하면서 반응이 진행된다. 생성물은 가스크로마토그래피, 질량분석스펙트럼, 핵자기공명스펙트럼, 적외선스펙트럼 등으로 그 구조를 알았다.

• 한국수소및신에너지학회논문집
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• 제22권5호
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• pp.728-734
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• 2011

$LiFePO_4$ is a promising cathode material for secondary lithium batteries due to its high energy density, low cost and safety. $LiFePO_4$ was synthesized by the citrate process under reductive, neutral, and oxidative, atmospheres and the crystal structure was analyzed by X-ray powder diffraction. The samples synthesized under $N_2$ and $H_2$ atmosphere showed a single phase of a olivine structure, where the samples synthesized under $O_2$ atmosphere exhibited second phase of $Fe2O_3$. All the samples synthesized at 400, 600 and $800^{\circ}C$ under $N_2$ atmosphere presented a single phase of olivine. Residual organic material was observed for the sample synthesized at $400^{\circ}C$. There was nearly no intensity difference between the samples synthesized at $600^{\circ}C$ and $800^{\circ}C$. The electrochemical characteristic of the $LiFePO_4$ synthesized at $600^{\circ}C$ in the $N_2$ atmosphere was analyzed. The result exhibited an high discharge capacity of 160 mAh/g at the first cycle, and 155-160 mAh/g after 45 cycles.

• 한국세라믹학회지
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• 제49권1호
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• pp.105-110
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• 2012

In this paper, a yellow phosphor $Sr_3SiO_5:Eu^{2+}$ that emits efficiently at the 450 nm excitation for warm white LED is studied. In addition, the effects of various flux $BaF_2$, $NH_4Cl$ on the emission spectra were investigated. The samples were synthesized through conventional solid state reaction under reducing atmosphere of 95% $N_2$-5% $H_2$ mixture at the high temperature. All phosphors showed a excitation band from 450 nm and broad band emission peaking at region of 580 nm. The optimal concentration of $BaF_2$ flux is 3 wt% for $Sr_3SiO_5$ with doping 0.05mol Eu phosphors fired in a reductive atmosphere. The phosphor showed highest emission peaking at 582 nm.

• 한국세라믹학회지
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• 제56권6호
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• pp.566-576
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• 2019

In this work, we investigated kaolinite raw materials from China, Vietnam, and Seongju (Korea) used for the manufacture of porcelain products in Korea. According to chemical analysis results, for the kaolinites from Seongju, more feldspar components containing CaO, K₂O, and Na₂O are found than in those from China or Vietnam, of which the composition is close to that of pure kaolinite. Through X-ray Rietveld quantitative analysis, kaolinite and muscovite are found to be the main phases for all the raw materials. Halloysite, quartz, gibbsite, and andesine are found at more than 5% for KM-85 (China), LKC-60 (Vietnam), KC-009 (China), and WA (Seongju). Absorption rate is on order of LKC-60 < KC-009 < KM-85 < PA < WA, and the sample, sintered in reductive atmosphere, exhibits the lowest absorption rate. Comparing the color of the sintered samples, kaolinites of KM-85, LKC-60, and KC-009 (L^*: 94 - 97%) show higher whiteness value than those of WA and PA (L^*: 82 - 91%).

• 자원리싸이클링
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• 제2권2호
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• pp.22-26
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• 1993

아연 제련잔사로부터 갈륨과 인디움을 동시에 회수하기 위한 연속공정도를 확립하고자 하였다. 갈륨만을 회수하는 알칼리처리법과는 달리 황산침출에 의할 경우 갈륨과 인디움의 동시회수가 가능하며, 2단계 중화를 통하여 용액중의 다량의 철분을 분리제거할 수 있었다. 1차처리하여 얻은 갈륨과 인디움의 침천물은 알칼리 및 산처리에 의해 갈륨과 인디움을 각각 분리회수할 수있었으며, 약산성 용액에서 저농도의 인디움을 회수하고자 할 경우 아연금속분말에 의한 cementation법을 사용하는 것이 효고적이었다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2016년도 제50회 동계 정기학술대회 초록집
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• pp.402.1-402.1
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• 2016

The performance of solid oxide fuel cells (SOFCs) is directly related to the electrocatalytic activity of composite electrodes in which triple phase boundaries (TPBs) of metallic catalyst, oxygen ion conducting support, and gas should be three-dimensionally maximized. The distribution morphology of catalytic nanoparticle dispersed on external surfaces is of key importance for maximized TPBs. Herein in situ grown nickel nanoparticle onto the surface of fluorite oxide is demonstrated employing gadolium-nickel co-doped ceria ($Gd0.2-xNixCe0.8O2-{\delta}$, GNDC) by reductive annealing. GNDC powders were synthesized via a Pechini-type sol-gel process while maximum doping ratio of Ni into the cerium oxide was defined by X-ray diffraction. Subsequently, NiO-GNDC composite were screen printed on the both sides of yttrium-stabilized zirconia (YSZ) pellet to fabricate the symmetrical half cells. Electrochemical impedance spectroscopy (EIS) showed that the polarization resistance was decreased when it was compared to conventional Ni-GDC anode and this effect became greater at lower temperature. Ex situ microstructural analysis using scanning electron microscopy after the reductive annealing exhibited the exsolution of Ni nanoparticles on the fluorite phases. The influence of Ni contents in GNDC on polarization characteristics of anodes were examined by EIS under H2/H2O atmosphere. Finally, the addition of optimized GNDC into the anode functional layer (AFL) dramatically enhanced cell performance of anode-supported coin cells.

• 한국결정성장학회지
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• 제29권6호
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• pp.317-328
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• 2019

본 연구에서는 도자기 제조용 원료(소지)에 사용되는 점토 광물의 물성 및 이로부터 제조된 소지의 품질을 조사하였다. 국내시장에 유통되고 있는 점토광물 중 중국에서 수입된 점토 (블랙점토, 홍점토, 백점토)와 충남 천안, 경남 산청에서 생산된 천안점토, 오부점토를 선택하여 비교 평가하였다. 화학분석 결과, 카올리나이트 등 1차 점토 외에 불순물로 CaO, K₂O, Na₂O을 포함하는 장석류(카리장석, 소다장석, 회장석)와 규석(SiO₂)이 포함되어 있으며 중국산 점토보다 국내 점토가 규석 및 장석질이 더 많이 함유되어 있음을 알 수 있었다. 도자기의 색상을 좌우하는 철분(Fe₂O₃)의 함량에 대해서는 천안점토, 오부점토, 홍점토의 경우 5 % 이상으로 붉은 색상을 띄며 중국산 (블랙점토, 백점토)에 비하여 철분 함량이 더 높음을 알 수 있다. X-선 결정상 분석을 통하여 원료광물에 존재하는 결정상의 종류를 분석한 결과, 원료 물질 모두 카올리나이트와 할로이사이트 등 1차점토와 함께 쿼츠(quartz)와 장석 등이 주요 결정상(main phase)으로 확인되었다. 이러한 점토광물을 원료로 하여 도자기용 소지를 제조하여 소결 후 물성을 평가하였다. 소성 후 수축률은 백자A급 < 백자B급 < 연분청 < 진분청 < 청자 소지 순으로 나타났으며 환원소성의 경우, 산화소성에 비하여 수축률이 높으며 이는 흡수율 결과와 일치하였다. 1250℃에서 환원소성한 경우, 매우 낮은 흡수율로 자화가 충분히 진행됨을 알 수 있다. 백자소지를 1200℃, 1250℃ 산화분위기에서 소성한 소성체가 환원소성한 소성체보다 백색도가 높으며, 백색도의 인자인 L^* 값이 86~95 %로 환원소성시 81~93 % 보다 높은 것을 알 수 있다. 철분 함량이 높은 청자소지나 분청소지의 경우, 환원분위기에서 소성한 소성체가 산화소성한 소성체보다 백색도가 높으며 a^*, b^* 값이 작은 양상을 확인할 수 있으며, 이는 Fe₂O₃ 산화물의 환원효과에 의한 것으로 판단된다.