• 한국세라믹학회지
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• 제19권2호
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• pp.157-161
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• 1982

The possibility of extraction of alumina from domestic Ha-dong kaolin was studied by sulfuric acid treatment. Raw kaolin was calcined at various temperature (500-110$0^{\circ}C$) and calcined kaolin were treated with sulfuric acid. The tendency of extraction yield of alpha alumina have been investigated by relating reaction time, temperature, and acid concentration. After reaction, precipitates were analyzed by DTA, TGA, and identified alpha alumina by X-ray diffractometer with calcined sample at 120$0^{\circ}C$. The results were as follows; 1. The optimum calcination temperature was 800-86$0^{\circ}C$. 2. The most suitable extracting conditions of alpha alumina were 40 wt%-$H_2SO_4$, 2-3 hours acid-treating time and 8$0^{\circ}C$ acid-treating temperature. 3. Precipitates were composed of $(NH_4)_2SO_4$, $Al_2SO_4(OH)_4$ 5-7 $H_2O$ and $Al(OH)_3$.

• 한국세라믹학회지
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• 제24권5호
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• pp.431-436
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• 1987

High purity Al2O3 has been extracted from serlcite of clayminerals, selicite was treated by H2SO4(2N∼18N) solution, NH4OH treatment(PH8.5∼10.0) and metallic impurities such as Fe were removed by NaOH treatment. The tendency of extraction yield of ${\alpha}$-Al2O3 have been investigated by relating reaction time, acid concentration. Reaction products were analyzed by DT-TGA, chemical analysis and X-ray diffractometer. Prepared ${\alpha}$-Al2O3 power is fired in air at 1400$^{\circ}C$, 1600$^{\circ}C$ 2hr. The results are as follows; 1. The most suitable extracting conditions of ${\alpha}$-Al2O3 from Selicite were N-H2SO4, 120 min acidtreating time. 2. The optimum pH condition was 9.0. 3. Physical properties of sintered Al2O3 bodies were as follows. Relative density is 99%. Water absorption is 0.26%. Rock well hardness is 89.

• Journal of Pharmaceutical Investigation
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• 제15권3호
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• pp.130-139
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• 1985

Inclusion compounds of suprofen with ${\alpha}-$ and, ${\beta}-cyclodextrins\;({\alpha}-CyD,\;{\beta}-CyD)$ were studied in comparison with suprofen alone and commercial suprofen capsules. Inclusion compound formations of suprofen with ${\alpha}-$, and ${\beta}-CyDs$ in aqueous solution and in solid state were confirmed by UV absorption, circular dichroism spectroscopies, IR spectroscopy, differential scanning calorimetry and X-ray diffraction measurements. Solid inclusion complexes were prepared by freeze-drying method, and their molar ratios were found to be 1 : 1. The dissolution rate of inclusion complexes of suprofen with CyDs was notably higher than that of suprofen alone.

• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2015년도 추계학술대회 논문집
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• pp.289-290
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• 2015

In this experiment, nitriding treatment has been performed at $400^{\circ}C$ with various $N_2$ content and with changing processing time on AISI 420 martensitic stainless steel to investigate the expanded martensite layer (${\alpha}^{\prime}_N$ layer) formation behavior. Nitriding was implemented with changing $N_2$ content from 10% to 25% for 15 hrs and processing time was changed from 4hr to 15hr at 25% $N_2$ content. After treatment, the behavior of the ${\alpha}^{\prime}_N$ layer was investigated by optical microscopy, X-ray diffraction, and micro-hardness testing. Potentiodynamic polarization test was also used to evaluate the corrosion resistance of the samples. It was found that the surface hardness and ${\alpha}^{\prime}_N$ layer thickness increases with increasing $N_2$ percentage and processing time. Although their corrosion behaviors are worse than the bare sample.

• 한국세라믹학회지
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• 제26권4호
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• pp.583-587
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• 1989

Various $\alpha$-silicon carbied and colloidal graphite particles were sintered at 155$0^{\circ}C$ in vacuum atmosphere by reaction bonding sintering method, and the physical properties and microstructural analysis of specimen were investigated. With decreasing particle size, sintered density and 3-point bending strength of materials were increased and 3.2${\mu}{\textrm}{m}$ specimen showed high density and strength, 3.05g/㎤, 40kg/$\textrm{mm}^2$, respectively. The results of X-ray diffractometer and optical micrographs analysis showed that graphite and silicon melt reacted to convert to fine $\beta$-SiC particle and the body was changed to dense material.

• 한국세라믹학회지
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• 제31권3호
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• pp.291-297
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• 1994

Cordierite powders were prepared by controlled hydrolysis of metal alkoxides with catalysts in water medium without using organic solvents. Water was adjusted to a certain pH by HC1 and NH4OH. $\alpha$-Cordierite powder was prepared from aluminum isopropoxide, tetraethyl orthosilicate and magnesium ethoxide mixed with water adjusted to pH of 3. At water pH of 11, $\alpha$-cordierite, mullite and $\beta$-quartz phases were coexisted. The powders were freeze dried, calcined and then fired at different temperatures. The characteristics of powders were examined by means of DTA, X-ray diffraction, FT-IR, and electron microscopy. It was found that $\alpha$-cordierite could be synthesized at temperature of 120$0^{\circ}C$ from the powders prepared by alkoxides with water medium without organic solvents.

• 약학회지
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• 제30권2호
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• pp.87-95
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• 1986

Inclusion complexation of $\alpha$-cyclodextrin($\alpha$-CD), $\beta$-cyclodextrin($\beta$-CD) and tri-O-methyl-$\beta$-cyclodextrin(tri-O-methyl-$\beta$-CD) with chlorpamide(CPA) in aqueous solution and in the solid state were studied by the solubility method, spectroscopy (UV, IR), differential scanning calorimetry (DSC) and powder X-ray diffractometry, and all their molar ratios were found to be 1:1. The solid complexes of CPA with three kinds of cyclodextrins were prepared by a freezedrying method, and their dissolution behaviors were examined. As a result, the release of CPA from the inclusion complexes was significantly improved. The intrinsic dissolution rate of CPA in cyclodextrin inclusion complexes was about 51 times ($\alpha$-CD inclusion complex) and 12 tmies ($\beta$-CD inclusion complex) larger than that of intact CPA.

• 한국주조공학회지
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• 제19권6호
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• pp.472-483
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• 1999

The effects of rapid solidification and Cr addition to the microstructure variations of the rapid solidified Ti-48Al-xCr(X = 2,4,6) alloys have been investigated using X-ray diffractometry, optical microscopy, scanning electron microscopy and transmission electron microscopy. The segregated coarse ${\gamma}$ phase was eliminated and the microstructure was refined by rapid solidification of the cooling rate of $10^4-10^6\;^{\circ}C/sec$. The lattice parameters and tetragonality of ${\gamma}$ phase decrease with the increase Cr content and by the rapid solidification. Non-equilibrium phase ${\alpha}$ remains at room temperature condition, which would be resulted from the restriction of phase transformation ${\alpha}$ to ${\alpha}_2+{\gamma}$.

• Bulletin of the Korean Chemical Society
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• 제30권4호
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• pp.846-848
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• 2009

Two modifications of the ${\alpha}\;and\;{\beta}$ forms of propyl mercaptan nickel(II) cluster, [$Ni_6(SCH_2CH_2CH_3)_{12}$], have been synthesized and their crystal structures have been determined by single-crystal X-ray diffraction. The alkyl groups are away from $Ni_6$ ring in $\alpha$ form whereas they are near to the Ni atom in $\beta$ form. The distance of Ni-H in $\beta$ form [2.576(5) $\AA$] is much shorter than that in $\alpha$ form [3.101(2) $\AA$]. In the crystal lattice of $\beta$ form, the whole structure forms a flower shape.

• 한국자기학회지
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• 제14권2호
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• pp.71-75
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• 2004

$\alpha$-LiFe $O_2$ 분말을 졸겔법을 이용하여 제조하였다. 결정학적 및 자기적 성질을 x-선 회절분석기, Mossbauer 분광기 및 진동형시료자화율측정기를 이용하여 연구하였다. $600^{\circ}C$에서 3시간 동안 공기 중에서 열처리하여 제조한 시료는 $\alpha$-LiFe $O_2$+LiFe $O_{8}$의 혼상으로 이루어졌으며 $600^{\circ}C$에서 3시간 동안 $H_2$(5%)/Ar(Bal.)혼합가스 분위기에서 열처리 한 시료는 $\alpha$-LiFe $O_2$ 상임을 확인할 수 있었다. X-선 회절분석 결과 $\alpha$-LiFe $O_2$ 분말은 cubic구조를 가졌으며 이때 격자상수 a=4.1930$\pm$0.0005 $\AA$이었다 Mossbauer 스펙트럼 분석결과 $\alpha$-LiFe $O_2$의 Neel온도는 130$\pm$3K임을 알 수 있었다.