• Journal of the Korean Applied Science and Technology
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• v.37 no.6
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• pp.1545-1555
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• 2020

In the present study, we investigated the antioxidant activity of Aucklandia lappa Decne (AL). Cell viability was measured in an MTT assay. Antioxidant effects were evaluated based on total polyphenol/flavonoid contents, ABTS radical scavenging activity, DPPH radical scavenging activity, SOD activity, and ROS content. AL was found not to be toxic at concentrations of 1 ㎍/mL, 10 ㎍/mL, and 100 ㎍/mL, respectively. The phenolic content was higher in AL-D than in AL-E, while the flavonoid content was higher in AL-E than in AL-D. AL-E exhibited higher ABTS radical scavenging activity than AL-D, and the EC50 values for BHA were 217.1 ㎍/mL in AL-D and 180.5 ㎍/mL in AL-E. AL-E also showed the highest DPPH radical scavenging activity. EC50 values for BHA were 114.2 ㎍/mL in AL-D and 95.8 ㎍/mL in AL-E. The SOD-like activity of AL-E was higher than that of AL-D. The EC50 values for ascorbic acid were 48.5 ㎍/mL in AL-D and 72.9 ㎍/mL in AL-E, indicating that both AL extracts have a SOD activity higher than that of ascorbic acid. AL-E reduced relatively more ROS than AL-D. With 100 ㎍/mL AL-E, the reduction level was almost similar to that of dexamethasone. Our results demonstrate that AL have antioxidant effects, and we believe that they could be very valuable as raw materials for anti-aging products, based on their antioxidant activity.

• Journal of the Korean Ceramic Society
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• v.22 no.6
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• pp.37-41
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• 1985

Several $Al_2O_3$-based polycrystalline which had different dopant ratio in the range of 0.5mol% were prepared by doping pure $Cr_2O_3$, $ZrO_2$, $HfO_3$ Single crystalline which had same composition with above polycrystalline were made by means of floating zone method. This study examined the role of each dopant for enhancing the mefchanical properties of $Al_2O_3$-based Ceramics. Optical micrographs $({\times}200)$ of $Al_2O_3-Cr_2O_3$ single crystal showing not only radial crack (rc) on the specimen surface but median crack (mc) and lateral crack (lc) under surface at the edge of indentation mark. Fracture toughness of $Al_2O_3$-based Ceramics was increased with $ZrO_2$ content. Alloying effect of $Cr_2O_3$ contributed to the hardness of $Al_2O_3$ based ceramics.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2013.05a
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• pp.78-79
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• 2013

As a part of study to maximize the amount used of the ground granulated blast-furnace slag, the study deals with setting properties of paste that is mixed the ground granulated blast-furnace slag with CaO-Al₂O₃ based inorganic blinder. The results of the experiment show that the setting time is most fast in the mix of 25% rate of CaO-Al₂O₃ based inorganic blinder. It is generally needed 2 hours for work time in precast concrete products. In this study, this requirement is achieved when using the retarder of 0.5%.

• Journal of Powder Materials
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• v.28 no.6
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• pp.502-508
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• 2021

SiAlON-based ceramics are a type of oxynitride ceramics, which can be used as cutting tools for heat-resistant super alloys (HRSAs). These ceramics are derived from Si3N4 ceramics. SiAlON can be densified using gas-pressure reactive sintering from mixtures of oxides and nitrides. In this study, we prepare an α-/β-SiAlON ceramic composite with a composition of Yb_0.03Y_0.10Si_10.6Al_1.4O_1.0N_15.0. The structure and mechanical/thermal properties of the densified SiAlON specimen are characterized and compared with those of a commercial SiAlON cutting tool. By observing the crystallographic structures and microstructures, the constituent phases of each SiAlON ceramic, such as α-SiAlON, β-SiAlON, and intergranular phases, are identified. By evaluating the mechanical and thermal properties, the contribution of the constituent phases to these properties is discussed as well.

• Transactions of Materials Processing
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• v.8 no.3
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• pp.227-227
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• 1999

The effects of intermediate annealing (IA) and the final cold rolling (CR) condition on the microstructure and sagging resistance during brazing were investigated using three layer clad sheets composed of the Al-7.5 wt.%Si alloy (filler, thickness: 10 ㎛)/Al-1.3 wt.%Mn based alloy (core, 80㎛)/Al-7.5 wt.%Si alloy (filler, 10㎛). Also, the effect of 1.2∼2 wt.% Zn addition into the core on the sagging resistance of the clad sheets was determined. It was revealed that all the clad sheets fabricated by the optimum condition (IA at 690 K and CR to 20∼45%) show excellent sagging resistance with a limited erosion due to the formation of a coarsely recrystallized grain structure in the core during brazing. It was also revealed that the recrystallization behavior of the Al-1.3 wt.%Mn based alloy is hardly affected by the addition of 1.2-2 wt.%Zn during the brazing cycle. Therefore, the sagging resistance of the clad sheets is found to be governed not by the Zn content added in the A1-1.3wt.%Mn based core, but by the intermediate annealing and final cold rolling condition.

• Journal of Powder Materials
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• v.26 no.1
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• pp.22-27
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• 2019

In this study, the effects of powder size and composition on the reflectance of Al-Si based alloys are presented. First, the reflectance of Al-Si bulk and powder are analyzed to confirm the effect of powder size. Results show that the bulk has a higher reflectance than that of powder because the bulk has lower surface defects. In addition, the larger the particle size, the higher is the reflectance because the interparticle space decreases. Second, the effect of composition on the reflectance by the changing composition of Al-Si-Mg is confirmed. Consequently, the reflectance of the alloy decreases with the addition of Si and Mg because dendrite Si and $Mg_2Si$ are formed, and these have lower reflectance than pure Al. Finally, the reflectance of the alloy is due to the scattering of free electrons, which is closely related to electrical conductivity. Measurements of the electrical conductivity based on the composition of the Al-Si-Mg alloy confirm the same tendency as the reflectance.

• Korean Journal of Metals and Materials
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• v.49 no.12
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• pp.1001-1004
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• 2011

The formation of TiC and $Al_2O_3$ particles based on the self-combustion reaction of the $Al-TiO_2-C-CuO$ system in an Al alloy melt was investigated. With an adequate amount of CuO in the system, a spontaneous reaction occurred within the Al alloy melt at $850^{\circ}C$ and thereafter was self-maintained, producing an Al matrix composite reinforced with thermodynamically stable TiC and $Al_2O_3$ particles. TiC and $Al_2O_3$ particles contributed to a considerable increase in the strength and stiffness, demonstrating the feasibility of this method as a practical application for structural parts.

• Korean Journal of Materials Research
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• v.22 no.2
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• pp.82-85
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• 2012

The effect of the alloy systems Al-Mg alloy and Al-Si alloy in this study on the characteristics of die-casting were investigated using solidification simulation software (MAGMAsoft). Generally, it is well known that the casting characteristics of Al-Mg based alloys, such as the fluidity, feedability and die soldering behaviors, are inferior to those of Al-Si based alloys. However, the simulation results of this study showed that the filling pattern behaviors of both the Al-Mg and Al-Si alloys were found to be very similar, whereas the Al-Mg alloy had higher residual stress and greater distortion as generated due to solidification with a larger amount of volumetric shrinkage compared to the Al-Si alloy. The Al-Mg alloy exhibited very high relative numbers of stress-concentrated regions, especially near the rib areas. Owing to the residual stress and distortion, defects were evident in the Al-Mg alloy in the areas predicted by the simulation. However, there were no visible defects observed in the Al-Si alloy. This suggests that an adequate die temperature and casting process optimization are necessary to control and minimize defects when die casting the Al-Mg alloy. A Tatur test was conducted to observe the shrinkage characteristics of the aluminum alloys. The result showed that hot tearing or hot cracking occurred during the solidification of the Al-Mg alloy due to the large amount of shrinkage.

• Transactions of Materials Processing
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• v.31 no.6
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• pp.365-375
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• 2022

The microstructure and high-temperature plastic deformation behavior of the modified Al-0.7Mn alloy were investigated and compared with the conventional Al-0.3Mn (Al3102) alloy. α-Al (matrix) and Al₆(Mn, Fe) phases were identified in both alloys. As a result of microstructure observation, both alloys showed equiaxed grains, and Al-0.7Mn alloy showed larger grain size and higher Al₆(Mn, Fe) fraction than Al-0.3Mn alloy. High temperature compressive tests, the deformation temperatures of 410℃, 450℃, 490℃, 530℃ and strain rats of 10^-2/s, 10^-1/s, 1/s, 10/s, were conducted using Gleeble equipment. The flow stress values of Al-0.7Mn alloy were higher than that of Al-0.3Mn alloy at all strain rates and temperature conditions. Constitutive equations were presented using the flow stresses obtained from experimental results and the Zener-Hollomon parameter. In the true stress-true strain curves of the two alloys, the experimental and predicted values were in good agreement with each other. Based on the dynamic material model, eutectic deformation maps of Al-0.7Mn and Al-0.3Mn alloys were suggested, and the plastic instability region was presented. The modified Al-0.7Mn alloy showed a wider plastic instability region than that Al-0.3Mn alloy. Based on the process deformation maps, the MPE tube parts could be manufactured through the actual extrusion process using the suggested conditions.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.20 no.7
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• pp.587-593
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• 2007

Oil-based nanofluids were prepared by dispersing spherical and fiber shaped $Al_2O_3$ and AlN nanoparticles in transformer oil. Two hydrophobic surface modification processes using oleic acid (OA) and polyoxyethylene alkyl acid ester (PAAE) were compared in this study. The dispersion stability, viscosity and breakdown voltage of the nanofluids were also characterized. $(Al_2O_3+AlN)$ mixed nanofluid was prepared to take an advantage of the excellent thermal conductivity of AlN and a good convective heat transfer property of fiber shaped $Al_2O_3$. For $(Al_2O_3+AlN)$ particles with 1 % volume fraction in oil, the enhancement of thermal conductivity and convective heat transfer coefficient was nearly 11 % and 30 %, respectively, compared to pure transformer oil. The nanofluid, containing $Al_2O_3+AlN$, successfully lowered the temperature of the heating element and oil itself during a natural convection test using a prototype transformer.