• Title/Summary/Keyword: 홍채학

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Influence of calcination temperature on the structure of freeze-dried silica gel (동결건조 실리카 젤의 구조에 미치는 하소온도의 영향)

  • 최성준;박상희;박홍채
    • Journal of the Korean Crystal Growth and Crystal Technology
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    • v.13 no.2
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    • pp.73-78
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    • 2003
  • The influence of calcination temperature on the pore structure of freeze dried silica gel derived from tetraethyl orthosilicate (TEOS) was investigated using $N_2$adsorption and mercury intrusion techniques. Freeze dried material contained not only 4-6 nm sized mesopores and 6-10 $\mu\textrm{m}$ sized macropores, but minor micropores. The change of pore structure due to the increase of calcination temperature was dependant upon the degree of densification.

Preparation of Si-SiC Composites by Si-Infiltration (Si 침윤에 의한 Si-SiC 복합체 제조)

  • 김인술;장주민;오기동;박홍채
    • Journal of the Korean Ceramic Society
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    • v.29 no.9
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    • pp.750-756
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    • 1992
  • Reaction bonded si-SiC composites were prepared by silicon infiltration technique at temperature of 1$600^{\circ}C$ for 30 minutes in vaccum atmosphere. The microstructure and mechanical properties of Si-SiC composites were investigated and characterized. UF-15 and SE-10 as SiC powders, phenolic resin and carbon black as carbon source, and metallic silicon powder as molten Si source were used as starting materials. New SiC crystallines nucleatd and grown by reaction of Si and C were detected by TEM and SEM-EDS. The bonding between new and original SiC was found to be strong. But the wetting of SiC by unreacted metallic Si and the rapid grain growth of new SiC decreased density and fracture toughness. Fracture toughness and modulus of rupture of Si-SiC composite were about 3.2 MPa.m1/2 and 480 MPa, respectively.

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The Effect of Seeding on Preparation of $ZrO_2/Al_2O_3$ Composite by Sol-Gel Method (Sol-Gel법에 의한 $ZrO_2/Al_2O_3$ 복합체의 제조에 미치느 Seeding 효과)

  • 김선욱;주치홍;장윤식;손영국;박홍채
    • Journal of the Korean Ceramic Society
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    • v.30 no.7
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    • pp.571-577
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    • 1993
  • The effect of $\alpha$-Al2O3 seeding on preparation of zirconia/alumina gel fragment prepared by sol-gel processing was characterized through XRD, SEM, TG/DTA and IR analysis. Aluminum isopropoxide and zirconium butoxide were used as starting materials. $\alpha$-Al2O3 seeding restrained grain growth of alumina and zirconia, and decreased tetragonal to monoclinic phase transformation of zirconia on cooling. Therefore, fine zirconia-toughened alumina composite having the relative sintered density of about 98% of theoretical at 140$0^{\circ}C$ for 2h could be obtained.

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Effects of Processing Modifiers on Dispersion and Rheology of Nonaqueous Mullite/Zirconia System Suspensions (뮬라이트/지르코니아계 비수성 현탁액의 분산 및 레올로지에 미치는 공정보조제의 영향)

  • Kim, Ji-Hyun;Yang, Tae-Young;Lee, Yoon-Bok;Park, Chan;Park, Hong-Chae
    • Journal of the Korean Ceramic Society
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    • v.38 no.6
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    • pp.537-544
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    • 2001
  • 뮬라이트, 지르코니아, 뮬라이트/지르코니아 비수성 현탁액의 분산 및 레올로지에 미치는 공정보조제의 영향이 침전밀도, 점도, 입자크기를 측정함으로써 검토되었다. 현탁액의 분산안정성 (높은 침전밀도와 낮은 점도로 특징 된)은 분산제+가소제+결합제를 함유하는 경우에 비하여 분산제 또는 분산제+가소제를 함유하는 경우가 우수하였다. Ball mulling 후의 입자크기분포는 공정보조제의 종류에 거의 영향을 받지 않았다. 결합제를 부가적으로 함유하는 현탁액은 상대적으로 강한 shear thinning 거동을 나타내었다.

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Reaction Processes of the Formation of Mg-Al Spinel by a Thermal Decomposition of a Mixed Sulfate Hydrate (복합 황산염 수화물의 열분해에 의한 Mg-Al 스피넬의 생성반응)

  • 박홍채;오기동
    • Journal of the Korean Ceramic Society
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    • v.23 no.6
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    • pp.71-75
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    • 1986
  • The forming reaction processes of magnesium aluminate spinel by a thermal decomposition of sulfate hydrate were studied with DTA, TG. SEM and X-ray powder diffraction methods. The hydrous salt composed of the mixture of the two compounds of $MgSO_4$ $6H_2O$ and ${AL_2}({SO_4})_17H_2O_3$ in which both sulfates were crystalline. On heating the hydrous slat the crystalline magnesium and aluminum sulfate anhydride to amorphous alumina magnesium sulfate anhydride decomposed to amorphous magnesia and these amorphous oxides reacted completely each other to form a spinel at $1000^{\circ}C$ The apparent activation energy of forming reaction of spinel was 36.5 kcal/mole($900^{\circ}C$~$1000^{\circ}C$) The crystallite size of spinel obtained at $1000^{\circ}C$ after 1 h was 380$\AA$.

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Preparation of Fine Titanium Nitride Powders from Titanium Trichloride (염화티타늄(III)으로부터 질화티타늄 미분체의 합성)

  • 이진호;장윤식;박홍채;오기동
    • Journal of the Korean Ceramic Society
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    • v.27 no.7
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    • pp.916-924
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    • 1990
  • The preparatin of the fine TiN powders by reduction-nitridation of TiCl3-Al-N2 system was attempted in the temperature range from 350$^{\circ}$to 100$0^{\circ}C$. The formation mechanism and kinetics of TiN were examined, and the resultant TiN powder was characterized by means of XRD, PSA and SEM-EPMA methods. TiN was formed at temperatrue higher than $600^{\circ}C$. As an intermediate phase, AlTi was obtained. The apparent activation energy for the formation of TiN was approximately 4.2kcal/mole(600$^{\circ}$~90$0^{\circ}C$). The crystallite size and lattice constnat of TiN powder obtained in the temperature range from 600$^{\circ}$to 100$0^{\circ}C$ for 2h at the Al/TiCl3 molar ratio of 1.0 were 160~255A and 4.231~4.239A, respectively. According to PSA measurement, the mean particle size ranged from 14.0 to 14.8${\mu}{\textrm}{m}$.

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Sr-containing Hydroxyapatite for Bone Replacement (골 대체재로의 스트론튬(Sr)이 고용된 Hydroxyapatite)

  • Choi, Jung-Sin;Park, Hong-Chae;Yoon, Seog-Young
    • Journal of the Korean Ceramic Society
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    • v.45 no.10
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    • pp.589-593
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    • 2008
  • The hydroxyapatite with different amounts of strontium was synthesized with wet chemical technique. The structural, morphological and chemical characterizations for the prepared hydroxyapatite with various strontium amounts were carried out with XRD, SEM, EDS, and FT-IR. Strontium is quantitatively incorporated into hydroxyapatite where its substitution for calcium provokes a well distribution in the EDS mapping and a linear shift of the infrared absorption bands of the hydroxyl and phosphate groups, coherent with the greater ionic radius of strontium.

Development of Robust-to-Rotation Iris Feature Extraction Algorithms For Embedded System (임베디드 시스템을 위한 회전에 강인한 홍채특징 추출 알고리즘 개발)

  • Kim, Shik
    • The Journal of Information Technology
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    • v.12 no.4
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    • pp.25-32
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    • 2009
  • Iris recognition is a biometric technology which can identify a person using the iris pattern. It is important for the iris recognition system to extract the feature which is invariant to changes in iris patterns. Those changes can be occurred by the influence of lights, changes in the size of the pupil, and head tilting. This paper is appropriate for the embedded environment using local gradient histogram embedded system using iris feature extraction methods have implement. The proposed method enables high-speed feature extraction and feature comparison because it requires no additional processing to obtain the rotation invariance, and shows comparable performance to the well-known previous methods.

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Influence of $TiO_2$ on Sintering and Microstructure of Magnesia (마그네시아의 소결과 미세구조에 미치는 $TiO_2$의 영향)

  • 이윤복;박홍채;오기동
    • Journal of the Korean Ceramic Society
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    • v.31 no.5
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    • pp.471-476
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    • 1994
  • The influence of TiO2 addition on the sintering and microstructure of magnesia ceramics was studied. An excess amount of TiO2 over the solid solubility limit reacted with magnesia to form Mg2TiO4 compound above 130$0^{\circ}C$. The deviation of lattice parameter of MgO was estimated to be under 0.2% when existence of TiO2 in MgO. The addition of TiO2 markedly promoted the densification of MgO at comparatively low temperature and the sintered density of about 98% of the theorectical was obtained at 150$0^{\circ}C$, 2h. The densification was mainly governed by grain growth of MgO and the effect of Mg2TiO4 existing as a second phase on depression of grain growth of MgO was not exhibited.

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Nanoindentation Investigation of Mechanical Properties in Oxide Laminar Composites (Nanoindentation을 이용한 산화물 층상 복합체의 기계적 성질 평가)

  • 윤석영;백동주;양태영;박홍채
    • Journal of the Korean Ceramic Society
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    • v.40 no.7
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    • pp.667-671
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    • 2003
  • Tape cast laminar composites with alumina/zircon(reaction-bonded mullite/zirconia) as an inner layer and alumina/zirconia or mullite/zirconia as an outer layer have been fabricated by hot-pressing. The mechanical properties(hardness and Young's modulus) and microstructure of laminar composites were examined using a nanoindentation technique and Scanning Electron Microscopy (SEM), respectively. The indentation load-displacement curve revealed the existence of residual stress in laminar composites.