• Journal of the Korean Ceramic Society
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• v.23 no.2
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• pp.7-12
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• 1986

As the other silicate minerals such as kaolinite and pyrophyllite kyanite ($Al_2O_3$.$SiO_2$) is transformed to mullite and free silica or glassy phase at high temperature. Therefore $Al_2O_3$ is commonly added to kyanite in order to increase the mullite-yield. In case of $Al_2O_3$-addition mullite-yield depends on the reactivity of added $Al_2O_3$ with free silica which occurs from transformation of kyanite or exists as accessory minerals. It is well known that addition of activated $Al_2O_3$Al powder is added to kyanite to utilize the aluminothermal reac-tion of Al powder in reaction of mullite-formation.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2008.11a
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• pp.94-97
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• 2008

현재 전주 국내에서는 전주에 대한 관심이 조금씩 증가하는 추세지만 그 활용 영역은 많지 않다. 최근들어 휴대폰 관련 부품과 LCD디스플레이의 핵심부품인 도광판 사출금형에 집중되어 있다. 본 연구에서는 반도체 웨이퍼 절단용 블레이드 제작을 목표로 Ni 전주도금층에 조밀하게 $Al_2O_3$를 분산시키는데 목표를 삼았다. 전주(electroforming)를 이용한 Ni-$Al_2O_3$를 첨가한 설파민산 니켈욕에 Surfactant의 양을 조절하며 Sodium Lauryl Sulfate의 첨가량이 많아질수록 Nickel 전주도금층 표면에 $Al_2O_3$는 접착되어지지 않고, 도금층의 두께는 두꺼워졌다. Surfactant의 첨가로인하여 Ni 전주도금층의 표면 장력이 감소하여 $Al_2O_3$를 감싸고 Ni 전주도금층이 성장하여야하는데 교반하는 과정에서 $Al_2O_3$ 입자들이 용액의 흐름에 따라 떨어져 나갔다.

• Journal of the Korean Ceramic Society
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• v.34 no.6
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• pp.591-600
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• 1997

Al2O3/Al composites were produced by displacement reaction method, which was carried out by immersing the sintered silica preform, which was prepared from fused silica powder, in molten aluminum. Because the molten aluminum did not penetrate into the silica preform with higher than 20% of porosity when the displacement reaction was accomplished at 100$0^{\circ}C$ for 10 hours in air atmosphere, the optimum range of sintering temperature of silica preform was from 135$0^{\circ}C$ to 140$0^{\circ}C$. The microstructure of this Al2O3/Al composites showed three-dimentionally co-continuous alumina, which provides wear resistance and high stiffness, and aluminium which acts as a toughnening phase. The grain size of the alumina in composites did not change with the particle size of the silica preform. The exact shape of the preform was retained and a net-shaped composite was produced. The representative Al2O3/Al composite prepared in this study showed 3.30mg/㎤ of bulk density, 350-430 MPa of flexural strength, 7.0 MPa.m1/2 of fracture toughness, and good machinability.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.11b
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• pp.402-405
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• 2001

$(Ba_{0.6-x}Sr_{0.4}Ca_{x})TiO_{3}$ (x=0.10, 0.15, 0.20) ceramics were fabricated by the mixed-oxide method and their stuctural and dielectric properties were investigated with variation of composition ratio and an amount of $Al_{2}O_{3}$ (0.5, 1.0, 1.5. 2.0, 3.0 wt%) doping content. As a result of the X-ray diffraction BSCT specimens showed dense and homogeneous structure without presence of the second phase. The sintered density was decreased with increase an $Al_{2}O_{3}$ doping content. The Curie temperature and relative dielectric constant at room temperature were decreased with increasing an amount of $Al_{2}O_{3}$ doping content. The dielectric loss is minimum for BSCT doped with 1.5wt% $Al_{2}O_{3}$ content. The tunability was decreased with increasing an Ca content and is about 4.2% for BSCT(50/40/10) doped with 2.0wt% $Al_{2}O_{3}$ content.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.11a
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• pp.402-405
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• 2001

(Ba$\_$0.6-x/Sr$\_$0.4/Ca$\_$x/)TiO$_3$(x=0.10, 0.15, 0.20) ceramics were fabricated by the mixed-oxide method and their structural and dielectric properties were investigated with variation of composition ratio and an amount of Al$_2$O$_3$(0.5, 1.0, 1.5, 2.0, 3.0 wt%) doping content. As a result of the X-ray diffraction BSCT specimens showed dense and homogeneous structure without presence of the second phase. The sintered density was decreased with increase an Al$_2$O$_3$ doping content. The Curie temperature and relative dielectric constant at room temperature were decreased with increasing an amount of Al$_2$O$_3$ doping content. The dielectric loss is minimum for BSCT doped with 1.5wt% Al$_2$O$_3$ content. The tunability was decreased with increasing an Ca content and is about 4.2% for BSCT(50/40/10) doped with 2.0wt% Al$_2$O$_3$ content.

• Journal of the Korean Ceramic Society
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• v.38 no.5
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• pp.418-423
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• 2001

16 mole%의 CeO$_2$가 고용된 Ce-TZP 소결체 사이에 140~240$mu extrm{m}$ 두께의 Ce-TZP-5~30 vol% $Al_2$O$_3$중간층이 삽입된 층상복합체를 분말건식가압성형법에 의해 제조하였다. 소결온도는 $Al_2$O$_3$가 5~30 vol.% 첨가될 때 90% 이상의 소결밀도를 얻을 수 있도록 1$600^{\circ}C$로 정하였다. 이러한 3층 복합체에서 바깥의 Ce-TZP 지역에서의 파괴 형태는 입내파괴를 보여주었지만 $Al_2$O$_3$가 함유된 중간층에서는 입계파괴가 전이되면서 인성증가를 보여주었다. 이러한 층상 복합체의 경우 중간 층에 들어가는 Ce-TZP 중의 $Al_2$O$_3$함량이 30 vol.% 정도에 이르면 층간의 서로 다른 소결밀도 및 수축율, 열팽창계수 때문에 층간 소결 결함이 생겨 층간에서 균열의 전파가 큰 영향을 받음을 알 수 있었다. 반면 중간층의 $Al_2$O$_3$함량이 적을 경우 층간 결함이 생기지 않아 층간에서 균열의 전파가 별 영향을 받지 않음을 알 수 있었다.

• Korean Journal of Materials Research
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• v.8 no.11
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• pp.999-1004
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• 1998

$SrAl_2O_4$:$Eu^{2+}, Dy^{3+}$ 축광성 형광체의 합성에 있어서 $B_2O_3$는 일반적으로 고상반응의 촉진을 위한 플럭스로서 첨가된다. 본 연구에서는 플럭스로 첨가되는 $B_2O_3$가 $SrAl_2O_4$:$Eu^{2+}, Dy^{3+}$ 형광체의 결정구조 및 잔광 특성에 미치는 영향을 조사하였다. 합성된 $SrAl_2O_4$:$Eu^{2+}, Dy^{3+}$ 형광체는 520nm에서 최대 피크를 갖는 폭넓은 발광 스펙트럼을 나타내었고, $B_2O_3$ 첨가량의 5wt%일 때 최대값을 나타내었다. $B_2O_3$의 첨가에 의해 $SrAl_2O_4$:$Eu^{2+}, Dy^{3+}$ 결정 내부에는 균일 변형(uniform strain)이 발생하였고 이 결과로 결정격자의 a축과 c축의 길이 및 $\beta$각이 감소하여다. 그리고 $SrAl_2O_4$ 결정내부의 균일 변형은 $Eu^{2+}$이온의 여기과정에서 발생하는 정공(hole)의 포획 사이트인 음이온 결함(negative defect)을 다량 발생시키는 원인이 되고, 결과적으로 $SrAl_2O_4$:$Eu^{2+}, Dy^{3+}$ 결정의 잔광 특성을 향상시키는 것으로 생각되었다.

• Korean Chemical Engineering Research
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• v.56 no.3
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• pp.349-355
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• 2018

$BaMnAl_{11}O_{19}$ was prepared by urea-induced homogeneous precipitation and characterized by X-ray diffraction and scanning electron microscopy. At increased precipitant concentrations, AlOOH replaced $Al(OH)_3$ as an Al precursor. $BaMnAl_{11}O_{19}$ exhibited enhanced catalytic combustion performance and inhibited CO generation. Catalytic performance was also enhanced by the presence of $BaAl_2O_4$ and $BaMnAl_{11}O_{19}$. Compared to $BaAl_2O_4$, $BaMnAl_{11}O_{19}$ exhibited superior catalytic combustion activity.

• Journal of the Korean Chemical Society
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• v.21 no.1
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• pp.53-59
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• 1977

A method of synthesizing $NaAlCO_3(OH)_2$ (Dawsonite) and $KAlCO_3(OH)_2$, was investigated by blowing $CO_2$ gas into sodium and potassium aluminate solutions. The reactions were accomplished at a temperature of 80 to $90^{\circ}C$, while $CO_2$ gas was blowing into the solutions which the molar ratios of $Na_2O/Al_2O_3,\;and\;K_2O/Al_2O_3$ were 6 to 8 and 8 to 10, respectively. It was observed that highly purified Dawsonite and $KAlCO_3(OH)_2$ are produced when Alumina is present in Boehmite at an equilibrium solid phase with a large amount of $HCO_3^-$ in the solutions. The rational formulas of Dawsonite and $KAlCO_3(OH)_2$synthesized under the conditions should be expressed as $NaAlO(OH)HCO_3\;and\;KAlO(OH)HCO_3$, respectively, by IR analysis. In addition, electron microscopic observation also indicated that Dawsonite in a fibrous crystal and $KAlCO_3(OH)_2$ in a needleshaped crystal.

• Journal of Sensor Science and Technology
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• v.18 no.1
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• pp.48-53
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• 2009

$Eu^{2+}$-doped ${SrAl_2}{O_4}$ and $Eu^{2+}$, $Dy^{3+}$ co-doped ${SrAl_2}{O_4}$ phosphors have been synthesized by conventional solid state method. Photocurrent properties of $Eu^{2+}$ doped ${SrAl_2}{O_4}$ and $Eu^{2+}$, $Dy^{3+}$ co-doped ${SrAl_2}{O_4}$ phosphors, in order to elucidate $Dy^{3+}$ co-doping effect, during and after ceasing ultraviolet-ray (UV) irradiation have been investigated. The photocurrent of $Eu^{2+}$, $Dy^{3+}$ co-doped ${SrAl_2}{O_4}$ phosphors during UV irradiation was 4-times lower than that of $Eu^{2+}$-doped ${SrAl_2}{O_4}$ during UV irradiation, and 7-times higher than that of $Eu^{2+}$-doped ${SrAl_2}{O_4}$ after ceasing UV irradiation. The photocurrent results indicated that holes of charge carriers captured in hole trapping center during the UV irradiation and liberated after-glow process, and made clear that $Dy^{3+}$ of co-dopant acted as a hole trap. The photocurrent of ${SrAl_2}{O_4}$ showed a good proportional relationship to UV intensity in the range of $1{\sim}5mW/cm^2$, and $Eu^{2+}$-doped ${SrAl_2}{O_4}$ was confirmed to be a possible UV sensor.