• Journal of the Korean Vacuum Society
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• v.15 no.4
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• pp.395-403
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• 2006

It is known that $MgAl_2O_4$ has higher resistance to moisture than MgO, in humid ambient MgO is chemically unstable. It reacts very easily with moisture in the air. In this study, the characteristic of $MgAl_2O_4$ and $MgAl_2O_4/MgO$ layers as dielectric protection layers for AC- PDP (Plasma Display Panel) have been investigated and analysed in comparison for conventional MgO layers. MgO and $MgAl_2O_4$ films both with a thickness of $1000\AA$ and $MgAl_2O_4/MgO$ film with a thickness of $200/800\AA$ were grown on the Cu substrates using the electron beam evaporation. $1000\AA$ thick aluminium layers were deposited on the protective layers in order to avoid the charging effect of $Ga^+$ ion beam while the focused ion beam(FIB) is being used. We obtained sputtering yieds for the MgO, $MgAl_2O_4$ and $MgAl_2O_4/MgO$ films using the FIB system. $MgAl_2O_4/MgO$ protective layers have been found th show $24{\sim}30%$ lower sputtering yield values from 0.244 up to 0.357 than MgO layers with the values from 0.364 up to 0.449 for irradiated $Ga^+$ ion beam with energies ranged from 10 kV to 14 kV. And $MgAl_2O_4$ layers have been found to show lowest sputtering yield values from 0.88 up to 0.109. Secondary electron emission coefficient(g) using the ${\gamma}$- FIB. $MgAl_2O_4/MgO$ and MgO have been found to have similar g values from 0.09 up to 0.12 for indicated $Ne^+$ ion with energies ranged from 50 V to 200 V. Observed images for the surfaces of MgO and $MgAl_2O_4/MgO$ protective layers, after discharge degradation process for 72 hours by SEM and AFM. It is found that $MgAl_2O_4/MgO$ protective layer has superior hardness and degradation resistance properties to MgO protective layer.

• Journal of the Korean Ceramic Society
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• v.20 no.1
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• pp.25-30
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• 1983

This experiment was studied in the system of (1-x) CaO MgO $2SiO-Al_2O_3$ to investigate forming of solid solution. The technique empolyed was the well known water-quenching method. Differential thermal analysis of the each glass water quenched indicated that under 30 mole% $Al_2O_3$ was lowered with increasing of the amount of $Al_2O_3$ It was supposed by X-ray diffraction patterns of each specimen sintered at various temperature that only solid solution was formed under the 30mole % $Al_2O_3$ compositions solid solution and anorthite were formed at the 20mole% $Al_2O_3$ composition anorthite solid solution and spinel$(MgAl_2O_4)$ were formed over the 40mole% $Al_2O_3$ compositions. The maximum density and thermal expanison coefficient was 2.89g/cm 7.74x106./C$^{\circ}$ respectively in the composi-tion of 10 mole% $Al_2O_3$ . All the specimens showed linear thermal expansion behavior. Microhardness was as high as 850kg/nm2 in the composition of 5, 10, 20 mole % $Al_2O_3$ and dielectric constant was 7.3-6.9.

• Journal of the Korean Ceramic Society
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• v.25 no.1
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• pp.35-41
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• 1988

In the system of Li2O-MgO-Al2O3-Cr2O3, the crystalline solid solution of LiCrO2 along the pseudo-binary join between rocksalt structure(LiCrO2) and spinel structure(MgCr2O4 or MgAl2O4) have been investigated by x-ray diffraction techniques. In this study, order-disorder phase transition of LiCrO2 was observed and the unit cell of the disordered LiCrO2 structure has been established. It has been found that LiCrO2 makes a solid solution over a wide range with MgAl2O4, while not with MgCr2O4. This difference was explained as being due to the ability of oxygen lattice distortion which depended on the relative sizes and chemical bonding characteristics of the substituted ions.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.959-960
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• 2006

Li reacts with $N_2$ at room temperature. In order to activate Li, the mechanical milling of Li with stable metal oxide, namely, $Al_2O_3$ and MgO, using a high energy vibrating ball mill was performed. In the case of Li-MgO system, it reacts with $N_2$, but hardly reacts with $O_2$. The reaction with $N_2$ generally produces $Li_3N$, while for some vigorous reactions the $Mg_3N_2$ is produced as the major phases. In the case of $Li-Al_2O_3$ system, reactivities with both $N_2$ and $O_2$ are high. The difference is explained in terms of the reaction mechanism and the Li state.

• Journal of the Korean Ceramic Society
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• v.24 no.2
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• pp.117-122
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• 1987

Glass forming ranges in the AlF3-(Mg＋Sr＋Ba)F2-P2O5 system are studied and ultraviolet transmission, infrared transmission, coefficient of refractive index, thermal expansion coefficient, density and chemical durability of the glasses are determined. Glass forming range is restricted MgF2 0-10wt%, SrF2 10-50wt%, BaF2 10-40wt% in this system. While BaF2 is substituted by SrF2, density and refractive index are decreased, micro hardness and thermal expansion coefficient are increased according to the increasing of SrF2 at fixed MgF2 contents. These samples represent high transmittance(93%) from 400nm to 3800nm and chemical durability of these samples show less than 0.3mg/$\textrm{cm}^2$$.$hy by weightloss.

• Journal of Power System Engineering
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• v.12 no.1
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• pp.66-71
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• 2008

Alumium alloys hot forging process are gaining increased acceptance in the automotive and electronic industries and hot forging is one of the most efficient manufacturing method for mass product parts. It has been investigated the microstructures and mechanical properties of Al-11.7Si-0.5Mg (KNT40-T6)alloy fabricated by hot forging process for development of connecting rod in this study. The microstructure of hot forged specimen was composed of eutectic structure of alumimum solid solution and $Mg_2Si$ precipitates. The tensile strength of solutionized Al-11.7Si-0.5Mg alloy was 217MPa. This alloy showed a good corrosion resistance using electrochemical polarization test.

• Journal of Advanced Marine Engineering and Technology
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• v.28 no.2
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• pp.300-308
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• 2004

The formation mechanism of anodic oxide films on Mg alloys when anodized in NaOH solution. was investigated by focusing on the effects of anodizing potential. Al content. and anodizing time. Pure Mg and Mg-Al alloys were anodized for 10 min at various potentials in NaOH solutions. $Mg(OH)_2$ was generated by an active dissolution reaction at the surface. and the product was affected by temperature. The intensity ratio of $Mg(OH)_2$ in the XRD analysis decreased with increasing applied potential. while that of MgO increased. The anti-corrosion properties of anodized specimens at each constant potential were better than those of non-anodized specimens. The specimen anodized at an applied potential of 3 V had the best anti-corrosion property. And the intensity ratio of $Mg_{17}Al_{12}$/Mg increased with aluminum content in Mg-Al alloys. During anodizing. the active dissolution reaction occurred preferentially in ${\beta}\;phase(Mg_{17}Al_{12})$ until about 4 mins. and then the current density increased radually until 7 mins. The dissolution reaction progressed in a phase(Mg) which not formed the intermetallic compound. which had a lower Al content. In the anodic polarization test of $0.017\;mol{\cdot}dm^-3$ NaCl and $0.1\;mol{\cdot}dm^-3\;Na_2SO_4$ at 298 K. the current density of Mg-15 mass% Al alloy anodized for 10 mins increased. since the anodic film that forms on the a phase is a non-compacted film. The anodic film on the phase for 30 mins was a compact film as compared with that for 10 mins.

• Journal of Korea Foundry Society
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• v.32 no.6
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• pp.289-295
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• 2012

Mg-Al-Sn-Si system alloy, as a promising cheap heat-resistant Mg alloy for automobile engine part, has been investigated. Refinement of microstructure and precipitation of thermally stable secondary phases are important goal for the design of heat-resistant Mg alloy. In this study, the effect of Ce on the microstructure and room temperature mechanical properties of Mg-Al-Sn-Si alloy was investigated. High thermally stable $Mg_2Si$ phases in Mg-Al-Sn-Si alloy is very useful intermetallic compound. However, the $Mg_2Si$ phases often result in poor mechanical properties due to the coarse chinese type $Mg_2Si$ phases. The experimental specimens were fabricated by fluxless melting under $CO_2+SF_6$ atmosphere and poured into the permanent pre-heated at $200^{\circ}C$. It was told that Ce addition can modify $Mg_2Si$ phases and refine microstructure and improve the tensile strength, yield strength and elongation.

• Journal of Surface Science and Engineering
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• v.40 no.5
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• pp.241-244
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• 2007

$MgF_2$/Cr/$MgF_2$, $MgF_2$/Cu/$MgF_2$ and $MgF_2$/Al/$MgF_2$ multi-layered thin films were fabricated by evaporation system. $MgF_2$ and Cr(Cu, And Al) was selected as a low refractive index material and mid reflector layer, respectively. Optical properties including color effect were systematically studied in terms of different film layer by using spectrophotometer. Experimental results were compared to the simulation result. The films consistings of $MgF_2$/Cr/$MgF_2$, $MgF_2$/Cu/$MgF_2$, $MgF_2$/Al/$MgF_2$ multi-layered thin films showed wavelength range of $430{\sim}780nm$, typically color range between greenish yellow and orange at view angle of $45^{\circ}$. It was confirmed that this experimental result was well matched with simulation result.

• Proceedings of the KWS Conference
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• 2002.10a
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• pp.612-619
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• 2002

The dynamic behavior of Al-Mg alloys plasma was very unstable and this instability was closely related to the unstable motion of keyhole during laser irradiation. The keyhole fluctuated both in size and shape and its fluctuation period was about 440 ${\mu}{\textrm}{m}$. This instability has been estimated to be caused by the evaporation phenomena of metals with different boiling point and latent heats of vaporization. Therefore, the authors have conducted the spectroscopic diagnostics of plasma induced in the pulsed YAG laser welding of Al-Mg alloys in air and argon atmospheres. In the air environment, the identified spectra were atomic lines of Al, Mg, Cr, Mn, Cu, Fe and Zn, and singly ionized Mg line, as well as strong molecular spectrum of AlO, MgO and AIH. It was confirmed that the resonant lines of Al and Mg were strongly self-absorbed, in particular in the vicinity of pool surface. The self-absorption of atomic Mg line was more eminent in alloys containing higher Mg. These facts showed that the laser-induced plasma was relatively a low temperature and high density metallic vapor. The intensities of molecular spectra of AlO and MgO were different each other depending on the power density of laser beam. Under the low power density irradiation condition, the MgO band spectra were predominant in intensity, while the AlO spectra became much stronger in higher power density. In argon atmosphere the band spectra of MgO and AlO completely vanished, but AlH molecular spectra was detected clearly. The hydrogen source was presumably the hydrogen solved in the base Metal, absorbed water on the surface oxide layer or H$_2$ and $H_2O$ in the shielding gas. The temporal change in spectral line intensities was quite similar to the fluctuation of keyhole. The time average plasma temperature at 1 mm high above the surface of A5083 alloy was determined by the Boltzmann plot method of atomic Cr lines of different excitation energy. The obtained electron temperature was 3, 280$\pm$150 K which was about 500 K higher than the boiling point of pure aluminum. The electron number density was determined by measuring the relative intensities of the spectra1lines of atomic and singly ionized Magnesium, and the obtained value was 1.85 x 1019 1/㎥.