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Determination of Hydroxyapatite Precipitation Condition from the $Ca-PO_4-H_2O$ System
오영제,Oh, Young-Jei 한국분석과학회 2000 분석과학 Vol.13 No.2
수산화물, 탄산염 및 수산화아파타이트(HAp)의 형성과 해리는 용액의 pH에 따라 달라지며 $Ca-PO_4-H_2O$계로부터 균질하고 미세한 HAp, $Ca_{10-x}(HPO_4)_x(PO_4)_{6-x}(OH)_{2-x}(x=0)$, 세라믹 분말을 제조하는데 매우 중요한 인자가 된다. 각 복합이온의 용해도는 pH와 직선적인 관계에 있으므로 용해도 도형은 수산화물, 탄산염 및 수산화아파타이트(HAp)의 평형상수와 용해도적으로부터 계산된 대수 몰농도로 그릴 수 있다. $Ca-PO_4-H_2O$계로부터 $25^{\circ}C$에서 단일상의 $Ca_{10-x}(HPO_4)_x(PO_4)_{6-x}(OH)_{2-x}(x=0)$ 분말을 제조하기 위한 최적의 pH조건은 이론적인 고찰 결과 $10.5{\pm}0.5$로 결정되었다. 실온에서 제조하여 $80^{\circ}C$에서 건조시킨 HAp분말은 75nm의 입자크기를 갖는 미세한 응집분말 이었으며, $1,000^{\circ}C$에서 하소시킨 HAp분말은 450nm 크기의 거의 균질한 형태의 분말을 얻었다. HAp분말들이 응집되어 있었지만 소결후 미세구조는 양호하여 우수한 기계적 특성을 보유하였다. The formation and dissolution of hydroxides, carbonates and hydroxyapatite (HAp), which depend on the pH of solution, are important factor for the preparation of homogeneous and fine HAp, $Ca_{10-x}(HPO_4)_x(PO_4)_{6-x}(OH)_{2-x}(x=0)$, ceramic powder from the $Ca-PO_4-H_2O$ system. Since the solubility of each complex ion is a linear function of pH, the solubility diagram can be obtained by plotting the logarithmic molar concentrations calculated from the values of the equilibrium constants and solubility products for hydroxides, carbonates, and hydroxyapatite. The optimum pH condition for the formation of single phase $Ca_{10-x}(HPO_4)_x(PO_4)_{6-x}(OH)_{2-x}(x=0)$ powder in $Ca-PO_4-H_2O$ system at $25^{\circ}C$ was estimated as $10.5{\pm}0.5$ through the theoretical consideration. The HAp powder dried at $80^{\circ}C$ showed a fine agglomerated particles with a size of 75 nm. The HAp powder calcined at $1,000^{\circ}C$ consisted of nearly homogeneous particles with a size of 450 nm. Even though the dried HAp particles consisted of agglomeration, mechanical properties were superior due to fine microstructure after sintering.
Perovskite Gd₁-xSrxFeO₃-y(x = 0.0, 0.5)의 Mossbauer 연구
엄영랑(Young Rang Uhm),김철성(Chul Sung Kim),서정철(Jung Chul Sur),오영제(Young-Jei Oh) 한국자기학회 1998 韓國磁氣學會誌 Vol.8 No.2
Crystallographic and magnetic properties of perovskite Gd_(1-x)Sr_xFeO_(3-y) (x = 0.0, 0.5) substituted Sr²+ having larger ionic radius than Gd³+ at GdFeO₃ have been studied by x-ray diffraction, Mossbauer spectroscopy, and VSM. The crystal structures are found to be orthorhombic with the lattice parameters : a_0 = 5.53 Å, b_0=5.608 Å, c_0=7.724 Å for Gd_(0.5)Sr_(0.5)FeO_(3-y), Gd_(1-x)Sr_xFeO_(3-y) (x=0.0, 0.5) have been investigated over temperature range from 4.2 to 690 K using the Mossbauer technique. The Neel temperature of Gd_(1-x)Sr_xFeO_(3-y) system is 690 K with x value of 0.0 and 515 K with x value of 0.5. Analysis of Mossbauer spectra and Mohr's salt analysis for Gd_(1-x)Sr_xFeO_(3-y) demonstrated the existence of the mixed valence states of iron and the coordination state of Fe³+ and Fe⁴+ ions. The Corresponding hyperfine parameters for GdFeO₃ are compatible with S = 5/2 Fe³+ in octahedral coordination.
금속 전극 알루미나 박막 캐패시터의 전기적 특성에 미치는 미세구조의 영향
정명선,주병권,오영제,이전국,Jeong, Myung-Sun,Ju, Byeong-Kwon,Oh, Young-Jei,Lee, Jeon-Kook 한국재료학회 2011 한국재료학회지 Vol.21 No.6
The power capacitors used as vehicle inverters must have a small size, high capacitance, high voltage, fast response and wide operating temperature. Our thin film capacitor was fabricated by alumina layers as a dielectric material and a metal electrode instead of a liquid electrolyte in an aluminum electrolytic capacitor. We analyzed the micro structures and the electrical properties of the thin film capacitors fabricated by nano-channel alumina and metal electrodes. The metal electrode was filled into the alumina nano-channel by electroless nickel plating with polyethylene glycol and a palladium catalyst. The spherical metals were formed inside the alumina nano pores. The breakdown voltage and leakage current increased by the chemical reaction of the alumina layer and $PdCl_2$ solution. The thickness of the electroless plated nickel layer was 300 nm. We observed the nano pores in the interface between the alumina layer and the metal electrode. The alumina capacitors with nickel electrodes had a capacitance density of 100 $nF/cm^2$, dielectric loss of 0.01, breakdown voltage of 0.7MV/cm and leakage current of $10^4{\mu}A$.
허성철,최덕균,오영제,Heo, Sung-Cheol,Choi, Duck-Kyun,Oh, Young-Jei 한국전기전자재료학회 2004 전기전자재료학회논문지 Vol.17 No.10
Dry film method for large size of PDP(Plasma Display Panel) module has been actively investigated. This method for lead-free transparent dielectric formation depends on green sheet technology. By adjusting the composition of transparent dielectric powders and organics, uniformly dispersed slurry was fabricated, Viscosity of the slurry exhibited pseudoplastic behavior for tape casting, Cast green sheets were tested under tensile condition at room temperature. It was found that the increase in transparent dielectric powder and binder ratio leads to decrease in strain to failure of green sheets from 120 % to 34 % and from 255 % to 4 %, respectively. Tensile strength of green sheets decreased abruptly with increase of transparent dielectric powder ratio, with minimum at 0.13 MPa. On the other hand, tensile strength increased continuously from 0.1 MPa to 2.4 MPa with increase of binder ratio. The green sheets were attached on the glass substrate and heated by following firing schedule. As a result, the best result was obtained when fired at 580 $^{\circ}C$ for 15 min and had transmittance of 78 % in visible range 550 nm.
ZrO₂ - Y₂O₃ (YSZ) 중간층이 저 자장영역에서의 LSMO 박막의 자기저항 특성에 미치는 영향
심인보(In-Bo Shim),오영제(Young-Jei Oh),최세영(Se-Young Choi) 한국자기학회 1999 韓國磁氣學會誌 Vol.9 No.6
Water-based sol-gel법으로 La_(2/3)Sr_(1/3)MnO₃(LSMO)/YSZ/SiO₂/Si(100) 다결정체 박막을 제조하여 YSZ 중간층 도입에 따른 상온, 120 Oe의 저 자장영역에서 측정한 tunnel-type 자기저항 변화에 미치는 영향에 대하여 고찰하였다. 페롭스카이트 단일상을 갖는 미세한 LSMO 박막을 얻을 수 있었으며, YSZ 중간층을 도입하지 않은 박막의 자기저항 변화비는 최대 약 0.20 %이었으나, YSZ 중간층을 도입한 경우 자기저항비가 0.42 %로 증가하였다. 이러한 tunnel-type 자기저항의 증가 현상은 YSZ 중간층이 SiO₂/Si(100) 기판과 La_(2/3)Sr_(1/3)MnO₃ 자성박막 사이에서 확산 장벽층으로서의 역할을 수행하여 LSMO 박막의 미세구조 특성 향상 및 확산반응에 의하여 생성된 dead layer를 감소시켜 나타난 결과이다. La_(2/3)Sr_(1/3)MnO₃(LSMO)/YSZ/SiO₂/Si(100) polycrystalline thin films were fabricated by chelated sol-gel method The effect of YSZ buffer layer at low field (120 Oe) spin-polarized tunneling magnetotransport (TMR) properties of LSMO thin film was studied at room temperature. Single perovskite LSMO thin films was obtained. The maximum TMR ratio was increased from 0.2 to 0.42 % by the insertion of YSZ buffer. YSZ as diffusion barrier was attributed to the fine microstructure of LSMO thin films and the reduction of dead layer between LSMO and SiO₂/Si(100) interfaces.
ZrO₂ - Y₂O₃ (YSZ) 중간층이 저 자장영역에서의 LSMO 박막의 자기저항 특성에 미치는 영향
심인보(In-Bo Shim),오영제(Young-Jei Oh),최세영(Se-Young Choi) 한국자기학회 1999 韓國磁氣學會誌 Vol.9 No.6
Water-based sol-gel법으로 La_(2/3)Sr_(1/3)MnO₃(LSMO)/YSZ/SiO₂/Si(100) 다결정체 박막을 제조하여 YSZ 중간층 도입에 따른 상온, 120 Oe의 저 자장영역에서 측정한 tunnel-type 자기저항 변화에 미치는 영향에 대하여 고찰하였다. 페롭스카이트 단일상을 갖는 미세한 LSMO 박막을 얻을 수 있었으며, YSZ 중간층을 도입하지 않은 박막의 자기저항 변화비는 최대 약 0.20 %이었으나, YSZ 중간층을 도입한 경우 자기저항비가 0.42 %로 증가하였다. 이러한 tunnel-type 자기저항의 증가 현상은 YSZ 중간층이 SiO₂/Si(100) 기판과 La_(2/3)Sr_(1/3)MnO₃ 자성박막 사이에서 확산 장벽층으로서의 역할을 수행하여 LSMO 박막의 미세구조 특성 향상 및 확산반응에 의하여 생성된 dead layer를 감소시켜 나타난 결과이다. La_(2/3)Sr_(1/3)MnO₃(LSMO)/YSZ/SiO₂/Si(100) polycrystalline thin films were fabricated by chelated sol-gel method The effect of YSZ buffer layer at low field (120 Oe) spin-polarized tunneling magnetotransport (TMR) properties of LSMO thin film was studied at room temperature. Single perovskite LSMO thin films was obtained. The maximum TMR ratio was increased from 0.2 to 0.42 % by the insertion of YSZ buffer. YSZ as diffusion barrier was attributed to the fine microstructure of LSMO thin films and the reduction of dead layer between LSMO and SiO₂/Si(100) interfaces.