• Journal of the Korean Society for Heat Treatment
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• v.24 no.6
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• pp.318-326
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• 2011

This study has been performed to investigate the effect of Al addition on High Temperature Gas Nitriding (HTGN) in 13%Cr-0.16%C stainless steel with different Al contents of 0.54%, 1.76% and 2.36%, respectively. HTGN treatment was carried out at $1100^{\circ}C$ for 1 hr, 5 hrs and 10 hrs. Nitrogen-permeated surface layers showed round type carbides of $Cr_{23}C_6$ and needle type nitrides of AlN in the matrix of martensite, representing 600~700 Hv. And the thickness of the surface layer increased with increasing Al content and HTGN treatment time. The inner region that was not permeated nitrogen showed chromium carbides in the mixed phase of martensite and ferrite for the 0.53% Al alloyed steel, however chromium carbides in the matrix of ferrite single phase were shown for the steels with the addition of 1.76%Al and 2.36%Al, representing the hardness of ~200 Hv. During nitrogen permeation from surface to the interior, substitutional elements of Cr, Al and Si moved toward the surface and interstitial element of carbon also moved from interior to the surface. This movement of alloying elements leads high concentration of these elements at the outmost surface, subsequently the lowest peak of substitutional elements were shown in the vicinity of near surface. After showing the lowest peak, the high concentration region of Al and C were formed due to the continuous movement of Al toward the surface. The long discontinuous precipitates of $Cr_{23}C_6$ and AlN were formed along the outmost surface owing to the high concentration of these alloying elements.

• Journal of the Korean Ceramic Society
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• v.47 no.6
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• pp.566-571
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• 2010

Dispersion behavior of the slurries consisted of bimodal-type AlN powders was examined in non-aqueous solvent system. Azotropic solvent system and copolymer acidic dispersant were applied to the slurries. Measurements of the sedimentation height and the viscosity of the each slurry, and the test of particle size distribution of the each powder sample were conducted as examinations for the dispersion behavior at the various dispersant contents. The bimodal-type particle size distribution was continued after addition of the dispersant and small particle portions were increased as the dispersant content increases. The density of the green sheet was also increased as the dispersant content increases and a green density of $2.114\;g/cm^3$ was obtained at the sample prepared from 2.4 wt% dispersant content. The increase of large particle portions resulted in the surface defects of the green sheets.

• Journal of the Korean Ceramic Society
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• v.47 no.6
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• pp.503-508
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• 2010

$Eu^{2+}$-doped $\beta$-SiAlONs ($Si_{6-z}Al_zO_zN_{8-z}:Eu_y$) are recognized as promising phosphor materials to build an white LED for lighting application due to its excellent absorption/emission efficiency in the long wave length region. In this research, the fabrication of $\beta$-SiAlON:Eu plate phosphor by sintering was investigated with fixed Eu content(y) and varied composition of the host lattice(z). The addition of the activator $Eu_2O_3$ lead to enhanced densification by forming the transient liquid phase. The refinement of a composition by the calculated lattice parameter indicated that the measured composition of the fabricated specimens is nearly same to that of designed one. The single phase $\beta$-SiAlON:Eu plate with relative density of 96.4% was achieved by addition of 2 wt% CaO, which implies the possibility of full densification by adjusting the processing variables.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2009.10a
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• pp.213-216
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• 2009

In this study, three cold-rolled TRIP steels containing different Al content (0.04wt%, 1.0 wt.% and 2.00wt%) were fabricated to understand the complex effects of Al in TRIP steel. The influences of Al on microstructural evolution of cold-rolled TRIP steels have been analyzed by using advanced analysis techniques, such as transmission electron microscope (TEM) and three dimensional atom probe tomography (3D-APT). TEM results revealed that second phases such as bainte and retained austenite decrease with increase of Al content. In addition, 3D-APT was used to characterize atomic-scale distribution of alloying elements at the constituent phases. Through these analysis techniques, the advanced characteristics of constituent microstructure in TRIP steels were identified depending on Al contents in TRIP steels.

• Journal of the Korean Ceramic Society
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• v.29 no.7
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• pp.511-516
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• 1992

In this study, SiC powder and Si powder were used as the raw materials. Mixture was prepared with addition of Al2O3 and Fe2O3 at 0.1~0.5wt% respectively. After this step, the mixture was pressed and nitrided for 30 hrs at 140$0^{\circ}C$ under NH3-N2 atmosphere. Mechanical properties of sintered specimens were investigated from measurement of porosity, bulk density and three point bending test. nitration reaction extent was observed at the change of mass before and after reaction, and the microstructure and the change of $\alpha$-Si3N4 and $\beta$-Si3N4 were observed by XRD and SEM. In the current work, the results are as follows 1. When Fe2O3 added, the nitridation increased with the content of Fe2O3, and the bending strength was increased from 0.1 wt% to 0.3 wt%, and decreased to 0.5 wt%. 2. When Al2O3 added, the nitridation and the bending strength increased little by little with the content of Al2O3 3. The bending strength of the specimen added with Fe2O3 were higher than that with Al2O3. Because the specimens contained Fe2O3 had much more the whisker type crystal of Si3N4 contributing to strength than contained Al2O3.

• Corrosion Science and Technology
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• v.16 no.3
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• pp.100-108
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• 2017

In this investigation corrosion behavior of newly developed high-pressure die cast Al-Ni (N15) and Al-Ni-Ca (NX1503) alloys was studied in 3.5% NaCl solution. The electrochemical corrosion behavior was evaluated using open circuit potential (OCP) measurement, potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS) techniques. Potentiodynamic polarization results validated that NX1503 alloy exhibited lower corrosion current density ($i_{corr}$) value ($5.969{\mu}A/cm^2$) compared to N15 ($7.387{\mu}A/cm^2$). EIS-Bode plots revealed a higher impedance (${\mid}Z{\mid}$) value and maximum phase angle value for NX1503 than N15 alloy. Equivalent circuit curve fitting analysis revealed that surface layer ($R_1$) and charge transfer resistance ($R_{ct}$) values of NX1503 alloy was higher compared to N15 alloy. Immersion corrosion studies were also conducted for alloys using fishing line specimen arrangement to simultaneously measure corrosion rates from weight loss ($P_W$) and hydrogen volume ($P_H$) after 72 hours and NX1503 alloy had lower corrosion rate compared to N15 alloy. The addition of Ca to N15 alloy significantly reduced the Al3Ni intermetallic phase and further grain refinement may be attributed for reduction in the corrosion rate.

• Bulletin of the Korean Chemical Society
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• v.32 no.8
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• pp.2537-2543
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• 2011

A self-assembled Al-bridged diiminopyridine-based ligand (3) was synthesized and characterized by FT-IR, ESI-MS and NMR spectroscopy. Electron spectral titrations were performed to confirm the formation of a novel trinuclear bis(imino)pyridyl iron(II) complex (4) upon addition of $FeCl_2$ into Al-bridged ligand 3 in methanol solution. Simultaneously, a typical bis(imino)pyridine-iron(II) complex (2) was synthesized and fully characterized. The X-ray crystal study of the iron(II) complex 2 disclosed a five-coordinate, distorted square-pyramidal structure with the tridentate N^N^N ligand and chlorides. The optimal molecular structure of 4 was obtained by means of molecular mechanics, which showed that each iron atom in the complex 4 is surrounded by two chlorides, a tridentate N^N^N ligand and one oxygen atom, supporting considerations about the possibility of six-coordinate geometry from MMAO or the ethylene access. A comparison of 4 with the reference 2 revealed a remarkable decrease of the catalytic activity and MMAO consumption (activity up to $0.41{\times}10^3\;kg\;{mol_{Fe}}^{-1}h^{-1}bar^{-1}$, Al/Fe = 650 for 4 and $7.02{\times}10^3\;kg\;{mol_{Fe}}^{-1}h^{-1}bar^{-1}$, Al/Fe = 1600 for 2).

• Journal of the Microelectronics and Packaging Society
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• v.14 no.1
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• pp.27-31
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• 2007

The cpapcitors with MIM(metal-insulator-metal) structures using PVP gate insulation films were prepared for the application of flexible organic thin film transistors (OTFT). The co-polymer organic insulation films were synthesized by using PVP(poly-4-vinylphenol) as a solute and PGMEA(propylene glycol monomethyl ether acetate) as a solvent. The cross-linked PVP insulation films were also prepared by addition of poly(melamine-co-formaldehyde) as thermal hardener. The leakage current of the cross- linked PVP films was found to be about 1.3 nA on Al/PES(polyethersulfone) substrate, whereas, on ITO/ glass substrate was about 27.5 nA indicating improvement of the leakage current at Al/PES substrates. Also, the capacitances of all prepared samples on ITO/glass and Al/PES substrates w ere ranged from 1.0 to $1.2nF/cm^2$, showing very similar result with the calculated capacitance values.

• Journal of the Institute of Electronics and Information Engineers
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• v.51 no.2
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• pp.33-37
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• 2014

We have developed a novel passivation process employing a sacrificial gallium oxide process in order to recover the surface damage in AlGaN/GaN HFETs. Even with a conventional prepassivation process, surface damage during high temperature ohmic annealing cannot be avoided completely. Therefore, it is necessary to recover the damaged surface to avoid the characteristic degradation. In this work, a sacrificial gallium oxide process has been proposed in which the damaged surface after ohmic annealing was oxidized by oxygen plasma treatment and thereafter etched back using HCl. As a result, the leakage current was dramatically reduced and thus the subthreshold slope was significantly improved. In addition, the maximum drain current level was increased from 594 to 634 mA/mm. To verify the effects, the surface conditions were carefully investigated using X-ray photoelectron spectroscopy.

• Proceedings of the KAIS Fall Conference
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• 2011.05a
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• pp.141-143
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• 2011

Al-SBA-1(Si/Al = 40, 80 and 120) and Al,Mg-SBA-1 (Si/(Al+Mg) = 40 and 80) molecular sieves were synthesized and characterized. Acetalization of n-heptanal with methanol was studied under autogenous pressure between 80 and $150^{\circ}C$. Since protonation of n-heptanal was fast, addition of methanol to the same to formed hemiacetal slowly whereas conversion of hemiacetal to acetal was fast. The catalysts exhibited nearly similar conversion irrespective of their difference in acidity, and all of them showed more than 80 % conversion either at 80 or $100^{\circ}C$. Hence it is evident that the difference in acidity is not so important in differentiating the activity of the catalysts. The large pore size and hydrophilic and hydrophobic properties are suggested to be the main factors that control acetalization.