• Journal of Environmental Health Sciences
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• v.26 no.4
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• pp.1-8
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• 2000

The objective of this study was to identify the sources and to estimate the source contributions to the atmospheric TSP(total suspended particulate matter) and PM-10(particulate matter with aerodynamic diameters less than 10$\mu\textrm{m}$) concentration in Taegu area. A total of 84 samples was collected during the January to December 1999. TSP and PM-10 were collected on filters by portable air sampler, and heavy metals in TSP and PM-배 were analyzed by ICO(Inductively Coupled Plasma Spectrometery) after preliminary treatment. The results were follow as : First, annual average of TSP and PM-10 concentration was 123 and 69$\mu\textrm{g}$/㎥ respectively. The concentration of TSP and PM-10 were highest in winter season compared to other seasons. Second, the concentration of Al, Fe, Mn were higher in TSP than in PM-10, indicating that these heavy metals are generally associate with natural contributions. Third, metal combinations showed that a high correlation among concentrations of heavy metals were follows: As Al, Fe and Mn in TSP ; Ni, Cr, Cd and Pb in PM-10. Finally, Statistical analysis was performed using Principal Components Analysis(PCA) in order to find possible sources of the pollutants. The factor analysis was permitted to identify four major sources(soil/road dust resuspension, waste incineration, furl combustion, vehicular emission) in each fraction. These source accounted for at least 83, 85% of variance of TSP and PM-10 concentration in Taegu area.

• Journal of the Korean Vacuum Society
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• v.22 no.1
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• pp.20-25
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• 2013

ZnO:Al thin films deposited by RF magnetron sputtering were post-annealed and the electrical and optical properties of ZnO:Al thin films were investigated before and after anneling. We confirmed that the ZnO:Al thin film was affected by post-annealing temperature. As post-annealing temperature increases, crystallinity and transmittance in visible area (400~800 nm) of ZnO:Al thin films decreased. While sheet resistance of thin films increased sharply with increasing to $400^{\circ}C$. This result is due to reduce of carrier concentration caused by absorption of $O_2$ or $N_2$ at surface of thin film.

• Journal of the Korean Society for Heat Treatment
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• v.6 no.4
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• pp.194-203
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• 1993

Rapid solidified splats Al-(1, 3, 5Cr) Alloys were produced by atomization-splat quenching method. Effects of mechanical alloying on the structure and mechanical properties of rapidly solidified Al-(1, 3, 5)Cr alloys were studied. Degree of mechanical alloying of Al-(1, 3, 5)Cr alloys can be determined by observing the microstructural refinement, microhardness and microstructure of Al-(l, 3, 5)Cr splats during processing. In the initial stage of mechanical alloying of the Al-(1, 3, 5)Cr splats fracturing of the grain boundaries occured first, followed after fracturing of zone A regions. Saturation hardness of Al-(1, 3, 5)Cr alloys increased proportionally with increasing concentration of the solute (Cr). Age hardening was not observed in these alloys. Decomposition temperature of Al-1Cr splats after mechanical alloying was higher than that of Al-5Cr splats. The density of $Al_7$ Cr precipitates increased proportionally with increasing chromium content, as a result, there was a transition to finely and spherically dispersed phase after mechanical alloying.

• Journal of Powder Materials
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• v.26 no.3
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• pp.220-224
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• 2019

The aluminum (Al)/copper oxide (CuO) complex is known as the most promising material for thermite reactions, releasing a high heat and pressure through ignition or thermal heating. To improve the reaction rate and wettability for handling safety, nanosized primary particles are applied on Al/CuO composite for energetic materials in explosives or propellants. Herein, graphene oxide (GO) is adopted for the Al/CuO composites as the functional supporting materials, preventing a phase-separation between solvent and composites, leading to a significantly enhanced reactivity. The characterizations of Al/CuO decorated on GO(Al/CuO/GO) are performed through scanning electron microscopy, transmission electron microscopy, and energy dispersive X-ray spectroscopy mapping analysis. Moreover, the functional bridging between Al/CuO and GO is suggested by identifying the chemical bonding with GO in X-ray photoelectron spectroscopy analysis. The reactivity of Al/CuO/GO composites is evaluated by comparing the maximum pressure and rate of the pressure increase of Al/CuO and Al/CuO/GO. The composites with a specific concentration of GO (10 wt%) demonstrate a well-dispersed mixture in hexane solution without phase separation.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1996.05a
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• pp.185-188
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• 1996

The doped n-type $Al_{x}Ga_{1-x}Sb$ crystals were grown by the vertical Bridgman method at composition ratio x=0, x=0.1, x=02 respectively. The lattice constants of the $Al_{x}Ga_{1-x}Sb$ crystals were 6.096${\AA}$, 6.097${\AA}$, 6.106${\AA}$ at composition ratio respectively. The carrier concentration, the resistivity, and the carrier mobility measured by the Van der Pauw method at x-0 were n≡1 x $10^{17}$$cm^{-3}$, $\rho$≡0.15 ${\Omega}$-cm, ${\mu}$$_{n}$≡500 $\textrm{cm}^2$$V^{-1}$$sec^{-1}$ at 300K. The carrier concentration, the resistivity, and the carrier mobility measured by the Van der Pauw method at x=0.1 were n≡2.96 x $10^{15}$$cm^{-3}$, $\rho$≡103 $\textrm{cm}^2$$V^{-1}$$sec^{-1}$ at 300K.

• Journal of Magnetics
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• v.12 no.4
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• pp.149-151
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• 2007

The AlCrN films were grown by RF reactive sputtering method under the selected conditions. The Cr concentration was varied by the number of Cr pieces placed on the Al target. The sample quality has been studied by XRD, Auger spectroscopy, optical absorption and electrical resistant measurements. The XRD and Auger results show that the samples consist of a major phase with the $Al_{1-x}Cr_xN$ formula, which has a hexagonal structure, and a few percents at. of oxygen, which may form $Al_2O_3$. There exist the Cr clusters in the samples with high concentration of Cr. The optical absorption measurement provides the information about the band gap that relates strongly to the quality of samples. The quality of samples is also clearly reflected in electrical measurement, i.e., the temperature dependence of resistance exhibits a semiconductor characteristic only for the samples that have no Cr cluster. In these cases, the values of ionization energies $E_a$ can be derived from R(T) plots by using the function R(T) = Ro exp $(E_a/k_BT)$.

• Journal of the Korean Ceramic Society
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• v.36 no.5
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• pp.513-520
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• 1999

Alumina-coated SiC whiskers wee prepared by the calcination (1150$^{\circ}C$, 1h, Ar) of the alumina hydrate layer which was precipitated homogeneously on whisker surface from a solution of Al2(SO4)3 and urea as a precipitant. In addition carbon coated SiC whiskers were prepared by the pyrolysis (1000$^{\circ}C$, 4h Ar) of phenolic resin coated whisker. The effects of coating conditions on the thickness and morphology of the coated layers were examined by SEM and TEM. It was found that Al2O3-coating layers become thinner and more uniform with decreasing the Al2(SO4)3 concentration. Thin (0.075-0.1$\mu\textrm{m}$) and uniformly alumina-coating layers were obtained at the Al2(SO4)3 concentration 0.010mol/l. On the other han carbon-coating layers were uniform but very thin (5-16 nm) in thickness. For thicker carbon-coating layers ethanol as a disperse medium was found to be more efficient compared tousing acetone.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.06a
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• pp.419-420
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• 2008

In this study, high quality (Al,N)-codoped p-type ZnO thin films were obtained by DC magnetron sputtering. The film on buffer layer grown in 80% $N_2$ ambient shows highest hole concentration of $2.93\times10^{17}cm^{-3}$. The films show hole concentration in the range of $1.5\times10^{15}$ to $2.93\times10^{17}cm^{-3}$, resistivity of 131.2 to 2.864 $\Omega$cm, mobility of 3.99 to 31.6 $cm^2V^{-1}s^{-1}$. The films on Si show easier p-doping in ZnO than those on buffer layer. The film on Si shows the highest quality of optical photoluminescence (PL) characteristics. The donor energy level $(E_d)$ of (Al,N)-codoped ZnO films is about 50 meV and acceptor energy level $(E_a)$ is in the range of 63 to 71 meV. It will help to improve p-type ZnO films.

• Korean Journal of Materials Research
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• v.25 no.10
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• pp.503-508
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• 2015

In this work, ceramic coatings were prepared on Al7075 aluminum alloy using microarc oxidation (MAO) process in a silicate-fluoride based electrolyte solution. The effect of $OH^-$ concentration, by adding NaOH to the solution on the microstructural and mechanical properties of the coating was investigated. Surface morphology and cross sectional view of the coating was analyzed using SEM while XRD was used to examine the phase compositions of the coatings. From XRD ${\alpha}-Al_2O_3$ phase was found to be increased by adding NaOH to the electrolyte. Thereby, the hardness and the wear properties of the MAO coatings were found to be superior to those of the coatings prepared without NaOH addition or with amount maximum than 2 g/l NaOH. Moreover, the morphology of the coatings was transformed form nodule-based cluster to crater based structure with the addition of NaOH to the MAO electrolyte solution.

• Proceedings of the KIEE Conference
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• 1987.07a
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• pp.465-468
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• 1987

This paper describes a model to calculate the equilibrium electron density of MODFET at the interface that takes into account the simultaneous shallow and deep level in the Al-GaAs layer. In the present study we have made an investigation of the interface electron density with different values of the AlGaAs doping density and spacer layer thickness, considering simultaneously two doner levels. In this case, the ratio of the shallow to the deep donor concentraction is considered. From the comparison with early experimental results we could find the deep level and that the deep donor concentration is about 50% with the Al mole fraction X ${\sim}0.3$, activation energy Edx=65meV, temperature $77^{\circ}K$ and spacer thickness range $50A{\sim}100A$. Also we have investigated the effect of the temperature. As temperature increase, at critical mole fraction X the nature of the donor concentration changes from $\Gamma$ to L and X.