• Journal of the Korean Ceramic Society
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• v.24 no.5
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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 the Korean Electrochemical Society
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• v.18 no.4
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• pp.161-171
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• 2015

High-yield zinc germanium oxide ($Zn_2GeO_4$) and zinc tin oxide ($Zn_2SnO_4$) nanowires were synthesized using a hydrothermal method. We investigated the electrochemical properties of these $Zn_2GeO_4$ and $Zn_2SnO_4$ nanowires as anode materials of lithium ion battery and sodium ion battery. The $Zn_2GeO_4$ and $Zn_2SnO_4$ nanowires showed excellent cycling performance of the lithium ion battery, with a maximum capacity of 1021 mAh/g and 692 mAh/g after 50 cycles, respectively, with a high Coulomb efficiency of 98 %. For the first time, we examined the cycling performance of $Zn_2GeO_4$ and $Zn_2SnO_4$ nanowires for sodium ion batteries. The maximum capacity is 168 mAh/g and 200 mAh/g after 50 cycles, respectively, with a high Coulomb efficiency of 97%. These nanowires are expected as promising electrode materials for the development of high-performance lithium ion batteries as well as sodium ion batteries.

• Journal of the Korean Recycled Construction Resources Institute
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• v.8 no.3
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• pp.294-301
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• 2020

This study evaluated the burnability and hydration reaction of clinker burned with high Al₂O₃ content OPC to apply large amounts of industrial by-products in the cement manufacturing process. Specifically, after preparing a clinker with a high C₃A content by burning the OPC raw material with a high content of Al₂O₃ in a laboratory electric furnace, the burnability of the clinker was evaluated through XRD Rietveld analysis and polarization microscopy, and clinker hydration reactivity was reviewed through the Isothermal conduction calorimetry analysis and the cement compressive strength. As a result, the kiln burning temperature for the production of high Al₂O₃ content clinker lower, and the compressive strength was equal to or higher than OPC. Therefore it was confirmed the possibility to manufacturing energy-saving high Al₂O₃ content clinker using a large amount of industrial by-products.

• Journal of the Korean Vacuum Society
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• v.21 no.5
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• pp.273-278
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• 2012

Over the last decade, the hafnium-based gate dielectric materials have been studied for many application fields. Because these materials had excellent behaviors for suppressing the quantum-mechanical tunneling through the thinner dielectric layer with higher dielectric constant (high-K) than $SiO_2$ gate oxides. Although high-K materials compensated the deterioration of electrical properties for decreasing the thickness of dielectric layer in MOSFET structure, their nano-mechanical properties of $HfO_2$ thin film features were hardly known. Thus, we examined nano-mechanical properties of the Hafnium oxide ($HfO_2$) thin film in order to optimize the gate dielectric layer. The $HfO_2$ thin films were deposited by rf magnetron sputter using hafnium (99.99%) target according to various oxygen gas flows. After deposition, the $HfO_2$ thin films were annealed after annealing at $400^{\circ}C$, $600^{\circ}C$ and $800^{\circ}C$ for 20 min in nitrogen ambient. From the results, the current density of $HfO_2$ thin film for 8 sccm oxygen gas flow became better performance with increasing annealing temperature. The nano-indenter and Weibull distribution were measured by a quantitative calculation of the thin film stress. The $HfO_2$ thin film after annealing at $400^{\circ}C$ had tensile stress. However, the $HfO_2$ thin film with increasing the annealing temperature up to $800^{\circ}C$ had changed compressive stress. This could be due to the nanocrystal of the $HfO_2$ thin film. In particular, the $HfO_2$ thin film after annealing at $400^{\circ}C$ had lower tensile stress, such as 5.35 GPa for the oxygen gas flow of 4 sccm and 5.54 GPa for the oxygen gas flow of 8 sccm. While the $HfO_2$ thin film after annealing at $800^{\circ}C$ had increased the stress value, such as 9.09 GPa for the oxygen gas flow of 4 sccm and 8.17 GPa for the oxygen gas flow of 8 sccm. From these results, the temperature dependence of stress state of $HfO_2$ thin films were understood.

• Journal of the Korean Ceramic Society
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• v.39 no.2
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• pp.153-158
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• 2002

$Al_2O_3$ composites powders with 1∼11 wt% $TiO_2$ were prepared by wet method and sintered at 1350$^{\circ}C$, 1450$^{\circ}C$ for 2h. Mechanical properties and microstructural evolution were investigated in this study. $Al_2O_3$-3 wt% $TiO_2$ composite were high bulk density of 2.37 g/$cm^3$ and low apparent porosity of 6.3%. The composites containing of 3 wt% $TiO_2$ showed moderately high bending strength of 68.9 MPa and the young's modulus of 35.5 MPa. The composites with increasing $TiO_2$ contents exhibit reduced thermal expansion coefficient due to the formation of $Al_2TiO_5$ phase.

• Journal of the Korean Ceramic Society
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• v.32 no.1
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• pp.83-89
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• 1995

YBa2Cu3O7-$\delta$, Y2BaCuO5, and binary compounds in the Ba-Cu-O system with the nominal composition of Ba2CuO3, BaCuO2, Ba3Cu4O7, Ba3Cu5O8 were synthesized to investigate the heat evolutions and crystalline phases in the hydration reaction of orthorhombic YBa2Cu3O7-$\delta$ phase. The observed crystalline phases were YBa2Cu3O7-$\delta$, Y2BaCuO5, and BaCuO2, or Ba2Cu3O5＋x, and some amount of noncrystalline phase in the Ba-Cu system comounds. In contact with distilled water, YBa2Cu3O7-$\delta$ and Y2BaCuO5 did not have considerable heat liberation, but in the binary compounds of the Ba-Cu-O system, the amount of total heat liberation was increased with respect to the Cu content. It might be that the reaction of high temperature superconductor YBa2Cu3O7-$\delta$ with water and/or moisture originated from the unusual oxidation state of Cu ion and the presence of amorphous Ba-Cu oxide compound. The degradation of high Tc superconductor by moisture and water could be controlled by restricting the heterogeneous distribution of Tc comlposition and the formation of second phase, such as stable Y2BaCuO5, and the resulting unstable Ba-Cu oxide compound.

• Korean Chemical Engineering Research
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• v.53 no.6
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• pp.776-782
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• 2015

$TiO_2-SnO_2$ nanoparticles with an average diameter of 3~5 nm were synthesized by hydrolysis of titanium tetraisopropoxide (TTIP) and tin chloride to depress the photocatalytic activity of $TiO_2$ nanoparticles. Organic-inorganic hybrid coating solutions were prepared by reacting the $TiO_2-SnO_2$ nanoparticles with 3-glycidoxypropyl trimethoxysilane (GPTMS) by the sol-gel method. The hard coating films with high refractive index were obtained by curing thermally at $120^{\circ}C$ after spin-coating the coating solutions on the polycarbonate (PC) sheets. The coating films from $TiO_2-SnO_2$ nanoparticles showed an improved pencil hardness of 3H compared to 2H of the coating films from $TiO_2$ nanoparticles. Besides, the refractive index of the coating films from $TiO_2-SnO_2$ nanoparticles enhanced from 1.543 to 1.623 at 633 nm as the Sn/Ti molar ratio increased from 0 to 0.5.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.11a
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• pp.262-263
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• 2008

The Metal-Insulator-Silicon (MIS) capacitors with $SiO_2$ and high-k dielectric were investigated. The high-k dielectrics were obtained by atomic layer deposit (ALD) system. The electrical characteristics were investigated by measuring the current-voltage (I-V) characteristics. The conduction mechanisms were analyzed by using the Fowler-Nordheim (FN) plot and Direct Tunneling (DT) plot. As a result, the MIS capacitors with high-k dielectrics have lower leakage current densities than conventional tunnel-barrier with $SiO_2$ dielectrics.

• Journal of IKEEE
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• v.26 no.1
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• pp.111-118
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• 2022

In this paper, we studied 4H-SiC CMOS that can be integrated with high-voltage SiC power devices. After designing the CMOS on a 4H-SiC substrate, we compared the electrical characteristics with the reliability of high temperature operation by TCAD simulation. In particular, it was confirmed that changing HfO₂ as the gate dielectric for reliable operation at high temperatures improves the thermal properties compared to SiO₂. By researching SiC CMOS devices, we can integrate high-power SiC power devices with SiC CMOS for excellent performance in terms of efficiency and cost of high-power systems.

• Journal of the Korean Ceramic Society
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• v.17 no.4
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• pp.203-207
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• 1980

The optical absorption of high index glasses of the system TiO2-BaO-B2O3 prepared from the raw materials for an optical waveguide glass has been measured in the near ultraviolet region. The amount of Ti3+ in the glass could be reduced to a level less than 5 ppm by melting a batch added with pure nitric acid, using a fused quartz crucible in an oxygen gas atmosphere. The ultra-pure glass of 10mm thick prepared in such a way did not show any appreciable color even for the one containing 30 mol% TiO2 and having refractive index nD of 1.84 and Abbe's number vD of 28.8. The wavelength of ultraviolet absorptin edge was longer for the glass of higher index and higher dispersdion. The melting of a TiO2 containing glass in a platinum crucible resulted in a coloration of the glass due to the dissolved plutinum from the crucible, which was more intense for the one containing larger amount of TiO2.