• Journal of the Korean Ceramic Society
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• v.31 no.3
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• pp.235-240
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• 1994

The electric and magnetic properties of Mg1.9-2xMn0.05Fe4xO4+${\gamma}$+2wt% Al2O3, and its microstructure have been investigated as a function of ferrite composition (x=0.45, 0.5, 0.55). The microstructure turned out to be independent on the ferrite composition. The resistivity was decreased with increasing Fe contents, whereas the Curie temperature decreased. Saturation magnetization was varied from 1741 to 2022 G with composition, and squareness ratio (SR), coercive force (BHc) were decreased and increased with increasing Fe contents respectively, so the sample which SR and BHc were 0.97 Oe and 1.49 Oe can be attainable at x=0.45.

• Applied Chemistry for Engineering
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• v.17 no.4
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• pp.369-374
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• 2006

$Rh-Pt/Al_{2}O_{3}$ catalysts were used for the first time to study its reaction characteristics in the asymmetric hydrogenation of ethyl pyruvate. The catalysts were prepared either by impregnation of Rh on a commercial $Pt/Al_{2}O_{3}$ or by sequential impregnation of Rh followed by impregnation of Pt on $Al_{2}O_{3}$. Reaction rate and enantiomeric excess (ee%) were compared according to the preparation method, Rh contents, and the reduction temperature of the catalyst. The physical characteristics of the catalysts were analyzed using XRD and TEM. Bimetallic $Rh-Pt/Al_{2}O_{3}$ catalysts showed an improved reaction rate and optical purity (63.6 ee%) with increasing the reduction temperature. The variation of the Rh contents as well as the preparation method elicited a big difference on the reaction rate, while enantiomeric excess (ee%) was lower (56~60%) with all bimetallic catalysts than with monometallic $Pt/Al_{2}O_{3}$ catalyst.

• Proceedings of the KIEE Conference
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• 1998.11c
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• pp.847-849
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• 1998

The effect of $Al_{2}O_{3}$ additives on the microstructure, mechanical and electrical properties of ${\beta}$-SiC+39vol.%$ZrB_2$ electroconductive ceramic composites by pressureless sintering were investigated. The ${\beta}$-SiC+39vol.%$ZrB_2$ ceramic composites were pressureless sintered by adding 4, 8, 12wt.% $Al_{2}O_{3}$ powder as a liquid forming additives at $1950^{\circ}C$ for 1h. Phase analysis of composites by XRD revealed mostly of $\alpha$-SiC(6H), $ZrB_2$ and weakly $\alpha$-SiC(4H), $\beta$-SiC(15R) phase. The relative density of composites was lowered by gaseous products of the result of reaction between $\beta$-SiC and $Al_{2}O_{3}$ therefore, porosity was increased with increased $Al_{2}O_{3}$ contents. The fracture toughness of composites was decreased with increased $Al_{2}O_{3}$ contents, and showed the maximum value of $1.4197MPa{\cdot}m^{1/2}$ for composite added with 4wt.% $Al_{2}O_{3}$ additives. The electrical resistivity of ${\beta}$-SiC+39vol.%$ZrB_2$ electroconductive ceramic composite was increased with increased $Al_{2}O_{3}$ contents, and showed positive temperature coefficient resistance (PTCR) in the temperature from $25^{\circ}C$ to $700^{\circ}C$.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.7 no.2
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• pp.224-234
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• 1997

In order to make high purity materials including low contents of interstitial impurities, 70 ㎾ electron beam melter was manufactured. The sponge Ti and Ti-6Al-4V alloy were required and melted by electron beam melter. Based on the experimental results of sponge Ti refining by electron beam melting, the purity of Ti was increased for 180 seconds but thereafter did not significantly vary. In addition, it was found that with number of melting, the purity of Ti did and vary but the yield of Ti was decreased. As a results of Ti refining, high purity Ti of 3N (99.9 wt%) could be obtained including interstitial impurities with total contents of which were maximum 900 ppm. From the experimental results of Ti-6Al-4V alloy electron beam melting, the amounts of Al loss could be estimated through thermodynamic data calculated from the regular solution model and the model of solute removal kinetics and the alloy composition calculated from the models was in accord with the experimental composition of the alloy, It took 10 minutes to make Ti-29Al-4V alloy calculated from the model into Ti-6Al-4V alloy and the composition of Ti-6Al-4V alloy was very homogeneous.

• Journal of the Korean Magnetics Society
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• v.7 no.4
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• pp.196-204
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• 1997

In order to study the effect of substituted $Al^{3+}$ of goethite, which was collected from Shinpyeongli in Cheju Island, we used X-ray diffractometer and Mossbauer spectrometer. In X-ray diffraction analysis, the X-ray diffraction peaks of goethite are not detected due to the high substituted Al contents of goethite. Isomer shifts indicated that the valence of Fe ions is almost oxidized trivalent of high spin state. It is believed that the contents of substituted diamagnetic $Al^{3+}$ for $Fe^{3+}$ is about 15.5 mol%. It seems that Neel temperature and saturated magnetic hyperfine field of the clay goethite are about 250 K and 498 kOe, respectively. For the temperature lower than Neel temperature, quadrupole splittings of the clay goethite are greatly influenced by $Al^{3+}$ substitution. It is believed that the high decrease of Neel temperature and magnetic hyperfine field of the clay goethite results from the magnetic dilution produced by substituting the diamagnetic $Al^{3+}$/TEX> for $Fe^{3+}$.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.11a
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• pp.106-106
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• 2009

Al-doped ZnO (AZO) thin films were grown on glass substrates by co-sputtering at room temperature. We made ZnO and Al target and ZnO:Al film is deposited with sputter which has two RF gun source. The Al content was controlled by varying Al RF power and effect of Al contents on the properties of ZnO:Al film was investigated. Crystallinity and orientation of the ZnO:Al films were investigated by X-ray diffraction (XRD), surface morphology of the ZnO:Al films was observed by atomic force microscope. Electrical properties of the ZnO:Al films were measured at room temperature by van der Pauw method and hall measurement. Optrical properties of ZnO:Al films were measured by UV-vis-NIR spectrometer.

• Corrosion Science and Technology
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• v.3 no.3
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• pp.98-101
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• 2004

The corrosion behavior of Al-Fe coatings was studied in the wet-seal atmosphere of molten carbonate fuel cells (MCFC). Fe-8Al, Fe-16Al, Fe-25Al, Fe-36Al, and Fe-70Al (in at.%) specimens were tested in Li/K carbonate at $650^{\circ}C$ by a single cell test and an immersion test. In general, the corrosion resistance of the Al-Fe coatings was enhanced due to the formation of a protective $LiAlO_2$ layer. However, when the Al-Fe coatings didn't have sufficient content of aluminum enough for maintaining the protective layer, the corrosion resistance of the Al-Fe coatings was severely degraded by the growth of non-protective scales like $LiAlO_2$. The test results revealed that the aluminum contents in the coatings should be higher than 25 at.% in order to form and maintain the protective $LiAlO_2$ layers.

• Korean Journal of Ecology and Environment
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• v.43 no.3
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• pp.377-384
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• 2010

Heavy metal accumulation levels of inhabitant fish, Hemibarbus labeo in Andong and Imha reservoirs were analyzed using an inductively coupled plasma spectrometer and atomic absorption spectrometer. Heavy metal contents of H. labeo from Andong reservoir were higher than those from Imha reservoir. Likewise, relative high contents of As, Cd and Hg were detected in the tissues from Andong reservoir. Among the heavy metals, Al, As and Fe were detected with high concentration in the gill tissues but not in the muscle tissues. Also, the average content of Zn was almost similar in all tissues. In addition, high accumulated level of Al, Cr, Cu and Mn were detected in gill and kidney tissues of H. labeo from Andong reservoir. As a result, the heavy metal contents from the inhabitant fishes, H. labeo, in Andong reservoir showed higher than those in Imha reservoir. We propose that heavy metal contamination in water and in inhabitated fishes is caused from various metals derived from water and sediments in water environment of Andong reservoir.

• Journal of Korean Society for Atmospheric Environment
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• v.3 no.1
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• pp.1-12
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• 1987

A series of supported sulfided Ni-W/$\gamma-Al_2O_3$ and Co-W/$\gamma-Al_2O_3$ catalysts with different nickel and cobalt contents were studied in the hydrodenitrogenation of pyridine dissolved in n-heptane. The ranges of experimental conditions were at the temperatures between 453 and 753 K, and the pressures between 30 and 50 Bar. The catalytic activities with different nickel and cobalt contents were shown to be maximum at Ni/Ni+W = 0.2 - 0.3, Co/Co+W = 0.3 - 0.4. Pyridine conversion increased with pressure and temperature and the step of piperidine formation was found to be irreversible. The reaction orders in Ni-W/$\gamma-Al_2O_3$ and Co-W/$\gamma-Al_2O_3$ catalysts were the first with respect to pyridine and reaction rate constants decreased with increase of initial pyridine concentration and their activation energies were 12.98 and 9.23 kcal/mol, respectively.

• Journal of Power System Engineering
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• v.10 no.2
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• pp.111-116
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• 2006

Tribologcal property of the ceramics used in severe condition was investigated and both $Al_2O_3$ ball and Al/SiC composite made by thermal spray process[TSP] were used as a specimen in this study. Four kinds of material couple in ball and disk specimens were tested in the dry condition by using ball-on-disk type tribo-tester. Friction coefficient, surface roughness, wear rate, and photograph of the worn surface were investigated. Generally, High SiC contents[$40{\sim}50%$] specimens showed very low friction coefficient below 0.05 and little wear rate in dry condition. And also, low SiC contents[0%] specimens showed a moderate wear rate and high coefficient of friction at the same condition.