• 한국자기학회:학술대회 개요집
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• 한국자기학회 2014년도 자성 및 자성재료 국제학술대회
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• pp.132-132
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• 2014

• 한국세라믹학회지
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• 제51권2호
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• pp.82-87
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• 2014

Due to the revised Korean standard KS L 5201 for Ordinary Portland Cement (OPC), the use of mixed cement has grown from 5% to 10%. This study investigates the hydration behavior of $C_3A$, asit is a cement mixture that is more commonly used than granulated blast furnace slag or limestone alone. Paste samples were prepared with either granulated blast furnace slag or limestone alone. Each sample was compared with the widely used Rietveld method with a cement mixture containing blast furnace slag or limestone. The hydration behavior of $C_3A$ in each OPC sample was assessed and results were analyzed. Granulated blast furnace slag promotes a high initial level of ettringite, but as the days passed, it promotes an increase in monosulfate, leading to cracks and expansion due to the penetration of sulfates in the solution. However, when limestone is added to the mixture, a transformation of ettringite to monosulfate occurs in the presence of the $CaCO_3$ in the limestone. It is considered that this produces hemi-carbonate and mono-carbonate and thus maintains the ettringite level.

• 한국건설순환자원학회논문집
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• 제8권4호
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• pp.514-519
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• 2020

본 연구에서는 시멘트 클링커의 원료 중 점토성분의 일부를 석탄재로 대체하여 시멘트 클링커를 각 온도별로 소성하여 시멘트 클링커의 광물상의 변화를 XRD-Rietveld법을 이용하여 정량분석하였다. 시멘트 클링커의 소성온도가 증가할수록 Belite의 양은 감소하고 Alite의 양은 증가하였으며, 유리 CaO의 양도 감소 되었다. Alite와 Belite의 형태는 1450℃ 이상에서부터 형태를 구분 할 수 있었으며. 1500℃ 소성에서는 결정의 크기가 조대하게 성장하여, 과소성이 진행된 것으로 판단된다. 유리 CaO의 경우 소성온도의 상승에 따라 감소하였고, 1450℃ 이상에서 0.5% 이하로 나타나, 1450℃ 이상에서는 충분한 소성이 이루어진 것으로 판단된다. 따라서 시멘트 클링커의 원료 중 알루미나질과 철질 원료의 화학성분 공급원으로서 석탄재의 활용이 가능한 것이 판단되었다.

• 한국결정학회지
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• 제9권1호
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• pp.48-52
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• 1998

Nd2O3, BaCo3, Co3O4를 출발물질로 하여 새로운 Nd3Ba5Co4O15상을 고상반응법에 의하여 합성하였다. 반응 온도는 1200℃ 로 하였고 열처리 중 반복적인 혼합을 실시하였다. Nd3Ba5Co4O15상의 결정구조는 분말 X-선회절법에 의한 데이터를 Rietveld법을 이용하여 정밀화하였다. 출발 모델은 Nd3.43Ba4.42Co2.23Al1.77O15의 결정구조를 따랐고 공간군 P63mc(186), 격자상수 a=11.636(5) Å, c=6.846(3) Å. 최종 신뢰도 R값은 Rwp=0.097, Rp=0.068로 나타났다. 이 상의 결정구조는 CoVICoIV3O15 클러스터로 구성되어 있고 이 클러스터는 CoVI 육면체가 3개의 CoIV 사면체와 corner sharing하는 형태를 보인다.

• 한국세라믹학회지
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• 제34권10호
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• pp.1045-1052
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• 1997

Barium ferrites (BaFe12O19) were synthesized at the various temperature by the coprecipitation-oxidation method. X-ray diffraction Rietveld analysis for barium ferrites were performed, their microstructures were observed and their magnetic properties were measured, in order to analyze the crystal structures and determine the optimal temperature of heat-treatment. The barium ferrite, its average particle size 80 nm, was formed at 600℃ through the hematite (α-Fe2O3), but the site occupations of the Fe's in tetrahedral and bipyramidal sites and of the Ba relatively low. Increasing the heating temperature, these occupations and the magnetization increased, and the crystal c-axis decreased. These changes were very small at the heat treatment of above 800℃, but the particles were rapidly grown. It is suggested that the optimal temperature of heat-treatment is 800℃, at which temperature crystal structure is relatively stable and the particles hardly ever grow.

• 한국결정학회지
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• 제14권2호
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• pp.110-114
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• 2003

LiAl/sub 0.24/Mn/sub 1.76/O/sub 4-y/S/sub y/ (y=0, 0.02) were synthesized by the sol-gel method. Both structures were refined by Rietveld method, its structure refined as a cubic spinel, space group Fd-3m, a=8.17937(30) Å and 8.18331(19) Å respectively. Though it has been made a charge/discharge experiment above 20 times, there was no change of 3 V/4 V capacity degradation. It was considered that the volume change of MnO/sub 6/ octahedron induced by sulfur substitution plays a key role in keeping the 3 V/4 V capacity. The refined composition of the compound could be confirmed with the ICP analysis.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2000년도 영호남학술대회 논문집
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• pp.196-199
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• 2000

Since the reports of CMR(colossal magnetoresistance) effects in some single crystal R-P phase $La_{1+x}Sr_{2-x}Mn_2O_7$, considerable researches have been carried out to find optimum composition and to understand the role of dimensionality in the CMR mechanism of this system. In this study, layered perovskite $Ln_xCa_{1-x}MnO_{4}$ (x=0.5, Ln=Pr, Nd, Sm, Gd) phases were synthesized by solid state reaction and their structures were refined by Rietveld method. Electrical and magnetic properties were measured between room temperature and liquid helium temperature and compared with those of two dimensional $La_{1.4}Sr_{1.6}Mn_2O_7$ phase.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2000년도 하계학술대회 논문집
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• pp.726-729
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• 2000

Though L $a_{1+x}$S $r_{2-x}$M $n_2$ $O_{7}$ n=2 R-P phases have been well known to have CMR effect, it was generally believed that n=1 phase was insulating. But recently monolayered perovskite $Ca_{2-x}$L $n_{x}$Mn $O_4$phase has been reported to show magnetoresistance. In this study, layered perovskite $Ca_{2-x}$L $n_{x}$Mn $O_4$ (x=0, 0.5, Ln=Pr, Nd, Sm, Gd) phases were synthesized by solid state reaction and their structures were refined by Rietveld method. The space groups of $Ca_2$Mn $O_4$, N $d_{0.5}$C $a_{1.5}$Mn $O_4$phases were refined as C2cb and Fmmm, respectively.y.ely.y.y.y.y.y.y.

• 한국결정성장학회지
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• 제28권4호
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• pp.152-158
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• 2018

PVT(Physical vapor transport)법은 고품질의 대면적 웨이퍼를 생산하기에 이점을 가져 질화물계 반도체의 상용화를 위해 많은 연구가 진행되고 있는 단결정 성장 방법이다. 하지만 복잡한 공정 변수들로 인하여 비평형적인 성장 조건을 갖게 될 경우 수많은 결함들이 발생하게 된다. 결정성장 후 어닐링 공정은 결정성 개선을 위해 널리 사용된다. 효과적인 결정성 개선을 위해서는 적절한 온도, 압력과 시간을 설정하는 게 중요하다. 본 연구에서는 PVT법으로 성장된 AlN 단결정 및 어닐링 조건에 따른 단결정의 결정 미세구조 변화를 X-ray topography, Electron Backscattered Diffraction(EBSD), Rietveld refinement를 통해 분석하였다. Synchrotron Whitebeam X-ray topography 분석 결과 어닐링을 진행하지 않은 단결정에 2차상 및 sub grain, impurity가 존재하였으며 이로 인해 결정성이 저하되는 것을 확인 할 수 있었다. EBSD 결과 어닐링을 진행한 시편의 경우 결정립수가 증가함과 동시에 basal plane의 뒤틀림이 일어나는 것을 관찰할 수 있었다. Rietveld refinement 결과 일부 격자들이 a, b, c축 방향으로 응력을 받아 변형된 것으로 분석되었다. 이는 어닐링 과정 중 hot zone 내의 상하 온도구배에 의해 발생한 응력으로 결정립 방향의 뒤틀림이 일어날 뿐만 아니라 격자 상수가 달라진 것으로 분석된다.

• 한국전기전자재료학회논문지
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• 제15권1호
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• pp.67-74
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• 2002

A phosphor for Plasma Display Panel, BaMgAl$_{10}$ O$_{17}$ :Eu$^{2+}$, showing a blue emission band at about 450nm was prepared by a solid-state reaction using BaCO$_3$, $Al_2$O$_3$, MgO, Eu$_2$O$_3$ as starting materials wish flux AlF$_3$. The study of the behaviour of Eu in BAM phosphor was carried out by the photoluminescence spectra and the Rietveld method with X-ray and neutron powder diffraction data to refine the structural parameters such as lattice constants, the valence state of Eu, the preferential site of Mg atom and the site fraction of each atom. The phenomenon of the concentration quenching was abound 2.25~2.3wt% of Eu due to a decrease in the critical distance for energy transfer of inter-atomic Eu. Through the combined Rietveld refinement, R-factor, R$_{wp}$, was 8.11%, and the occupancy of Eu and Mg was 0.0882 and 0.526 at critical concentration. The critical distance of Eu$^{2+}$ in BAM was 18.8$\AA$ at 2.25% Eu of the concentration quenching. Furthermore, c/a ratio was decreased to 3.0wt% and no more change was observed over that concentration. The maximum entropy electron density was found that the modeling of $\beta$-alumina structure in BaMgAl$_{10}$ O$_{17}$ :Eu$^{2+}$correct coincided showing Ba, Eu, O atoms of z= 1/4 mirror plane.e.ane.e.