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강대갑,송종택 한국결정성장학회 1995 한국결정성장학회지 Vol.5 No.3
금속티타늄 분말과 $H_2O_2$와의 반응물에 KOH용액을 첨가하는 습식법에 의해 티탄산칼륨 섬유를 합성하고, 합성된 생성물을 XRD, SEM, FT-IR 등에 의해 검토하였다. 습식 합성법의 경우, $KOH/TiO_2$ 몰비, 합성시간, aging 시간등이 주로 최종 생성물에 영향을 주었다. $KOH/TiO_2 = 1/1$, 합성시간 24시간, aging 시간 24시간 및 하소 온도 $900^{\circ}C$에서의 생성물은 주로 potassium tetratitanate이었으며, 10 ~ 20mm의 가늘고 긴 장섬유이었다. 합성시간이 길어질수록, 그리고 KOH량이 적어질수록, potassium tetratitanate는 potassium hexatitanate로 바뀌면서 섬유의 길이는 짧아졌다. The potassium titanate fibres were synthesized with wet process by the addition of KOH solution to the TiOz gel produced by the reaction between element titanium particles and $H_2O_2$ solution at $50^{\circ}C$. And then they were characterized by XRD, SEM and FT - IR. It was found that potassium titanate fibres were mainly affected by KOH/TiOz mole ratio, synthesis time and aging time in this wet process employed. For $KOH/TiO_2 = 1/1$, synthesizing time 24 hrs, aging time 24 hrs and calcination temperature of $900^{\circ}C$ for 1 hr, their products were mainly found to be potassium tetratitanate which had thin and long fibres in the range of 10 ~ 20 mm. As the synthesizing time increased and the amount of KOH decreased, potassium tetratitanate was converted into potassium hexatitanate. Also, the length of their fibres became short.
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이트리아 안정화 지르코니아에서 미세조직 설계에 따른 전기전도도와 파괴인성치의 적정화
강대갑,김선재 한국세라믹학회 1994 한국세라믹학회지 Vol.31 No.7
Using two kinds of ZrO2 powder stabilized by 8 mol% and 3 mol% of Y2O3 several microstructures were designed; two single composition specimens of 8 mol% Y2O3-ZrO3 and 3 mol% Y2O3-ZrO2 and five mixture specimens with multi-layered structure and particulate mixture structure at a mixing ratio of 1:1 by weight. Electrical conductivities were measured from 250 to 75$0^{\circ}C$ in air using an impedance analyser, and fracture toughness at room temperature using the indentation method. Making the mixture structures was more effective in enhancing fracture toughness than electrical conductivity. At low temperatures 3 mol% Y2O3-ZrO2 showed the highest values in both electrical conductivity and fracture toughness, while at high temperature the specimens of alternately stacked planar and coarse granulated structure were most favorable.
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강대갑,정충환 한국세라믹학회 1994 한국세라믹학회지 Vol.31 No.4
Compacts of mixed SiO2-Si powder were liquid phase sintered at 145$0^{\circ}C$ for up to 60 min in a hydrogen atmosphere. In contrast to the conventional microstructures of liquid phase sintered materials, the specimens showed that the solid phase of SiO2 formed a matrix while the liquid phase of Si was the dispersed in the solid matrix. The dispersion of liquid Si pockets was attributed to the high wetting angle of liquid Si on solid SiO2. Because of relatively high solubility of SiO2 in liquid Si at 145$0^{\circ}C$, SiO2 particles accommodated their shape via a solution-reprecipitation process. The liquid Si pockets grew by coalescing with their neighbour pockets. In the latter stage of the sintering, plate-shape grains appeared in the liquid Si pockets. The grains were SiO2 phase precipitated from the liquid Si which was oversaturated with oxygen during cooling to room temperature. By the formation and subsequent removal of the gaseous SiO phase due to the reaction between SiO2 and Si, the specimens became porous.
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강대갑,Weisskopf 한국세라믹학회 1987 한국세라믹학회지 Vol.24 No.5
Thermal expansions and thermal expansion coefficients of cordierite ceramics reinforced by SiC whiskers up to 40 vol. % were investigated. The composite specimens were hot pressed at 1523K for 30 min under 28.5 MPa pressing pressure in Ar atmosphere. Thermal expansions of the hot pressed composites were measured using a differential dilatometer up to 1262 K in air. Thermal expansions and thermal expansion coefficient of the composites increased with SiC whisker content. Thermal expansion behaviors of the composites were well explained by modelling parallel slabs randomly distributed on the whisker plane as the microstructural element of the composites.
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코디어라이트-SiC 위스커 복합재료의 기계적 성질과 강화기구
강대갑,Weisskopf 한국세라믹학회 1986 한국세라믹학회지 Vol.23 No.6
Flexural strength fracture toughness and strengthening mechanisms of cordierite ceramics reinforced by SiC whiskers up to 40vol% were investigated. The specimens were hot pressed at Ar atmosphere. The porosity increased with the SiC whisker content. Flexural strength and single edge notch beam fracture toughness were measured up to 1,000$^{\circ}C$. Extrapolating to zero porosity the reinforced composites exhibited in-creasings in flexural strength and fracture toughness with the SiC whisker content. The composites were strengthened mainly by load transfer crack impediment and partially by crack deflection mechanisms. Impurities played an important role in determining the mechanical properties of the composites.
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$Al_2O_3-SiC$ 위스커 복합재료의 기계적 특성
강대갑,권오종,Weisskopf 한국세라믹학회 1986 한국세라믹학회지 Vol.23 No.3
Mechanical properties of $Al_2O_3$ based composite ceramics reinforced by SiC whiskers up to 40% by volume we-re investigated. Specimens were hot pressed at $1, 500^{\circ}C$ under 28.5MPa for 30min in Ar atmosphere. Porosities room temperaturefracture toughnesses and flexural strengths up $1, 000^{\circ}C$ were measured. Porosities were increa-sed as the SiC whisker cortent increased. After compensating the effect of porosities that means extrapolated in zero porosities the reinforced composites exhibited increases in flexural strength and fracture toughness as the whi-sker content increased, .
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강대갑 한국전통과학기술학회 1996 한국전통과학기술학회지 Vol.3 No.1
As a preliminary study for scientific research of PaekJe-Togi earthenwares, several analysis methods frequently used in materials science were applied to a redintegrated PaekJe-Togi specimens. Through analyses of chemical elements, dilatometric behaviors, and X-ray diffraction patterns, scanning electron microscopy observations, and measurements of water absorption ratio and gas permeability, the redintegrated specimens exhibited their characteristics as follows; the microstructure inside was porous, the outside surface was covered with dense glassy layer composed of low melting elements such as Mg, and Ca, many small saliencies on outside surface with small pores were not covered by the glassy layer resulting a small gas permeability, and the sintering temperature re was estimated about 1300℃. However, for obtaining more reliable results and estimations from unknown ancient specimens, a large amount of data-base should be prepared and new measurement technologies be adopted.
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강대갑 에스케이텔레콤 (주) 2001 Telecommunications Review Vol.11 No.5
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