• Journal of the Korean Crystal Growth and Crystal Technology
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• v.28 no.4
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• pp.170-174
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• 2018

AlN crystal is been developing in global site for many years and 1 inch diameter wafer was already developed but it is demanding the efforts for the better quality. On the other hand, also the 2-inch size is developing recently to reduce the unit cost for manufacturing and to use to fabrication of the UV LED chips. In this study, we tried to evaluate the possibility of bulk AlN crystals on his thin films by PVT method. The AlN thin film was grown on SiC single crystal 2" wafer by HVPE method. We successfully grew AlN bulk crystal of a thickness of 7 mm using its thin film of a thickness of $10{\mu}m$ as a seed crystal. The resultants of AlN crystals were identified by metallurgical microscope, optical stereographic microscope and DCXRD measurement.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.28 no.3
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• pp.281-288
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• 2004

The hybrid composite material (Al/GFRP laminates) are applied to the fuselage and wing in a aircraft. Therefore, Al/GFRP laminates suffer from the cyclic bending moments. This study was to evaluate the effect of fiber stacking angle on the fatigue crack propagation and delamination behavior using the relationship between crack growth rate (da/dN) and stress intensity factor range (ΔK) in Al/GFRP laminates under cyclic bending moment. The variable delamination growth behavior in case of three different type of fiber orientations, i.e., [Al/O$_2$/Al], [Al/+45$_2$/Al] and [Al/90$_2$/Al] at the interface of Al layer and glass fiber layer was measured by ultrasonic C-scan images. As results of this study, It represent that the delamination shape should turns out to have more effective characteristics on the fiber stacking angle. The extension of the delamination zone in case of [Al/+45$_2$/Al] and [Al/90$_2$/Al] were not formed along the fatigue crack profile. The shape of delamination zone depend on fiber stacking angle and the variable type with the delamination contour decreased non-linearly toward the crack tip at the Al layer.

• Applied Chemistry for Engineering
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• v.30 no.6
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• pp.757-761
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• 2019

The catalytic yields of POM to hydrogen over M(1)-Ni(5)/AlCeO₃ (M = La, Ce, Y) were investigated using a fixed bed flow reactor under atmosphere. The crystal phase behavior of reduced La(1)-Ni(5)/AlCeO₃ catalysts before and after the reaction were studied via XRD analysis. FESEM and EDS analyses were further performed to show the uniformed distribution of La, Ni, and Ce metal particles on the catalyst surface. XPS results showed O^2-, O₂^2- species and metal ions such as Ce³⁺, Ce⁴⁺, La³⁺ and Ni²⁺ etc. were on the catalyst surface. When 1 wt% of La was added to Ni(5)/AlCeO₃ catalyst, Ni2p_3/2 and Ce3d_5/2 increased 52.7 and 6.3%, respectively. The yield of hydrogen on the La(1)-Ni(5)/AlCeO₃ catalyst was 89.1%, which was much better than that of M(1)-Ni(5)/AlCeO₃ (M = Ce, Y). As Ce⁴⁺ ions of CeO₂ produced by the reaction of AlCeO₃ with oxygen were substitute to La³⁺, it made oxygen vacancies in the lattice and further improved the hydrogen yield by increasing the dispersion of Ni atoms with strong metal-support interaction (SMSI) effect.

• Journal of the Korean Ceramic Society
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• v.22 no.6
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• pp.29-36
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• 1985

This study was carried out to research on the optimum condition of $MgAl_2O_4$ spinel synthesis and the chara-ceteristics of its sintered bodies. In this study the used materials-MgO $Al_2O_3$-were prepared from the extragrade chemicals $Mg(OH)_2 Al(OH)_3$ respectively. The tendency to spinel synthesis and sintering condition were discussed about additives of SEM and the characteristics of sintered bodies were measured by TMA etc, The results were as follows ; 1. The addion of $TiO_2$ promoted more effectively the sinterbility than that of $MnO_2$. 2. Residual $\alpha$-$Al_2O_3$ and MgO in theorectical composition samples were disappeared at 1$600^{\circ}C$ 3. When added MnO2 residual $\alpha$-$Al_2O_3$ and MgO were disappeared at 150$0^{\circ}C$ and 1$600^{\circ}C$ respectively. 4, . When added $TiO_2$ residual $\alpha$-$Al_2O_3$ and MgO were disappeared at 150$0^{\circ}C$ and 134$0^{\circ}C$ respectively.

• Journal of the Korean Ceramic Society
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• v.24 no.1
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• pp.9-16
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• 1987

Physical and electrical properties of ${\beta}$-Al2O3 were investigated as function of Na2O content from 6.67 wt.% to 13.19 wt.%. The majority phase is ${\beta}$-Al2O3 and the small amount of ${\beta}$"-Al2O3 exists in the specimens sintered at 1600$^{\circ}$for 30 mins. In the case of specimens with 8.54 wt.% Na2O sintered at 1600$^{\circ}C$, the relative amount of ${\beta}$-Al2O3 phase increases and that of ${\beta}$"-Al2O3 phase decreases with increasing sintering time, and then ${\beta}$"-Al2O3 phase does not exist if sintering time is over 8 hrs. As the Na2O content is increased, the 3-Point MOR and the resistivity are decreased. However, density and 3-Point MOR with increasing sintering time are decreased due to increasing the enclosed pore trapped inside of the exaggerated grains. As the sintering time is increased, the average grain size and the duplexity of microstructure are increased, and the resistivity is slightly decreased.

• Journal of the Korean Vacuum Society
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• v.17 no.4
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• pp.359-364
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• 2008

We have investigated optical and structural properties of $Al_{0.3}Ga_{0.7}N$/GaN and $Al_{0.3}Ga_{0.7}N/GaN/Al_{0.15}Ga_{0.85}N/GaN$ heterostructures (HSs) grown by metal-organic chemical vapor deposition, by means of Hall measurement, high-resolution X-ray diffraction, and temperature- and excitation power-dependent photoluminescence (PL) spectroscopy. A strong GaN band edge emission and its longitudinal optical phonon replicas were observed for all the samples. At 10 K, a 2DEG-related PL peak located at ${\sim}\;3.445\;eV$ was observed for $Al_{0.3}Ga_{0.7}N$/GaN HS, while two 2DEG peaks at ${\sim}\;3.42$ and ${\sim}\;3.445\;eV$ were observed for $Al_{0.3}Ga_{0.7}N/GaN/Al_{0.15}Ga_{0.85}N/GaN$ HS due to the additional $Al_{0.15}Ga_{0.85}N$ layers. Moreover, the emission intensity of the 2DEG peak was higher in $Al_{0.3}Ga_{0.7}N/GaN/Al_{0.15}Ga_{0.85}N/GaN$ HS than in $Al_{0.3}Ga_{0.7}N$/GaN HS probably due to an effective confinement of the photo-excited holes by the additional $Al_{0.15}Ga_{0.85}N$ layers. The 2DEG-related emission intensity decreased with increasing temperature and disappeared at temperatures above 150 K. To investigate the origin of the new 2DEG peaks, the energy-band structure for multiple AlGaN/GaN HSs were simulated and compared with the experimental data. As a result, the observed high- and low-energy peaks of 2DEG can be attributed to the spatially-separated 2DEG emissions formed at different AlGaN/GaN heterointerfaces.

• Journal of the Korean Chemical Society
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• v.55 no.4
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• pp.570-574
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• 2011

Large colorless single crystals of analcime with diameters up to 0.20 mm have been synthesized from gels with the composition of $3.00SiO_2$ : $1.50NaAlO_2$ : 8.02NaOH : $454H_2O$ : 5.00TEA. The fully $Na^+$-exchanged analcime have been prepared with aqueous 0.1 M NaCl (pH adjusted from 6 to 11 by dropwise addition of NaOH). The single-crystal structure of hydrated $|Na_{0.94}(H_2O)|[Si_{2.06}Al_{0.94}O_6]$-ANA per unit cell, a=13.703(3) ${\AA}$, has been determined by single-crystal X-ray diffraction technique in the orthorhombic space group Ibca at 294 K. The structure was refined using all intenties to the final error indices (using only the 1,446 reflections for which $F_o$ > $4{\sigma}(F_o))R_1/wR_2$ = 0.054/0.143. About 15 $Na^+$ ions are located at three nonequivalent positions and octahedrally coordinated. The chemical composition is $Na_{0.94}(H_2O)Si_{2.06}Al_{0.94}O_6$. The Si/Al ratio of synthetic analcime is 2.19 determined by the occupations of cations, 14.79, in the single-crystal determination work.

• Journal of the Korean Vacuum Society
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• v.17 no.1
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• pp.34-39
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• 2008

We have investigated the characteristics of $Al_{0.55}Ga_{0.45}N$/GaN heterostructures with and without low-temperature (LT) AlN interlayer grown by metalorganic chemical vapor deposition. The structural and optical properties were systematically studied by Rutherford backscattering spectroscopy (RBS), X-ray diffraction (XRD), optical microscopy (OMS), scanning electron microscopy (SEM), and photoluminescence (PL). The Al content (x) of 55% and the structural properties of $Al_xGa_{1-x}N$/GaN heterostructures were investigated by using RBS and XRD, respectively. We carried out OMS and SEM experiments and obtained a decrease of the crack network in $Al_{0.55}Ga_{0.45}N$ layer with LT-AlN interlayer. A two-dimensional electron gas (2DEG)-related PL peak located at ${\sim}3.437eV$ was observed at 10 K for $Al_{0.55}Ga_{0.45}N$/GaN with LT-AlN interlayer. The 2DEG-related emission intensity gradually decreased with increasing temperature and disappeared at temperatures around 100 K. In addition, with increasing the excitation power above 3.0 mW, two 2DEG-related PL peaks were observed at ${\sim}3.411$ and ${\sim}3.437eV$. The observed lower-energy and higher-energy side 2DEG peaks were attributed to the transitions from the sub-band level and the Fermi energy level of 2DEG at the AlGaN/LT-AlN/GaN heterointerface, respectively.

• Journal of the Korean Ceramic Society
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• v.23 no.3
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• pp.44-52
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• 1986

$Al_2O_3-ZrO_2$ ceramics was obtained by the co-precipitation method using $Al_2(SO_4)_2$.$18H_2O$ and $ZrOCl_2$.$8H_2O$ as starting materials $MgCl_2$.$6H_2O$ as a sintering aid and NH4OH as a hydrolyzing agent. The coprecipitate from the above raw materials was calcined at 125$0^{\circ}C$ for 1h and again sintered at 1$650^{\circ}C$ for 2h before measurements of strength hardness and fracture toughness. MgO addition was found to increase mechanical properties of the $Al_2O_3-ZrO_2$ system. The strength and frac-ture toughness of $Al_2O_3-ZrO_2$ ceramics were considered to be increased by stress-induced phase tranforma-tion of $ZrO_2$.

• Korean Journal of Materials Research
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• v.17 no.8
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• pp.447-451
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• 2007

We investigated the dependence of the various annealing conditions and thickness ($6\sim45nm$) of the Ti-doped $Al_2O_3$ coating on the electrochemical properties and the capacity fading of Ti-doped $Al_2O_3$ coated $LiCoO_2$ films. The Ti-doped-$Al_2O_3$-coating layer and the cathode films were deposited on $Al_2O_3$ plate substrates by RF-magnetron sputter. Microstructural and electrochemical properties of Ti-doped-$Al_2O_3$-coated $LiCoO_2$ films were investigated by transmission electron microscopy (TEM) and a dc four-point probe method, respectively. The cycling performance of Ti-doped $Al_2O_3$ coated $LiCoO_2$ film was improved at higher cut-off voltage. But it has different electrochemical properties with various annealing conditions. They were related on the microstructure, surface morphology and the interface condition. Suppression of Li-ion migration is dominant at the coating thickness >24.nm during charge/discharge processes. It is due to the electrochemically passive nature of the Ti-doped $Al_2O_3$ films. The sample be made up of Ti-doped $Al_2O_3$ coated on annealed $LiCoO_2$ film with additional annealing at $400^{\circ}C$ had good adhesion between coating layer and cathode films. This sample showed the best capacity retention of $\sim92%$ with a charge cut off of 4.5 V after 50 cycles. The Ti-doped $Al_2O_3$ film was an amorphous phase and it has a higher electrical conductivity than that of the $Al_2O_3$ film. Therefore, the Ti-doped $Al_2O_3$ coated improved the cycle performance and the capacity retention at high voltage (4.5 V) of $LiCoO_2$ films.