• Journal of Powder Materials
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• v.20 no.3
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• pp.197-202
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• 2013

A novel route to prepare Nd-Fe-B magnetic particles by utilizing both spray drying and reduction/diffusion processes was investigated in this study. Precursors were prepared by spray drying method using the aqueous solutions containing Nd salt, Fe salt and boric acid with stoichiometric ratios. Precursor particles could be obtained with various sizes from 2 to $10{\mu}m$ by controlling concentrations of the solutions and the average size of $2{\mu}m$ of precursors were selected for further steps. After heat treatment of precursors in air, Nd and Fe oxides were formed through desalting procedure, followed by reduction processes in Hydrogen ($H_2$) atmosphere and with Calcium (Ca) granules in Argon (Ar) successively. Moreover, diffusion between Nd and Fe occurred during Ca reduction and $Nd_2Fe_{14}B$ particles were formed. With Ca amount added to particles after $H_2$ reduction, intrinsic coercivity was changed from 1 to 10 kOe. In order to remove and leach CaO and residual Ca, de-ionized water and dilute acid were used. Acidic solutions were more effective to eliminate impurities, but Fe and Nd were dissolved out from the particles. Finally, $Nd_2Fe_{14}B$ magnetic particles were synthesized after washing in de-ionized water with a mean size of $2{\mu}m$ and their maximum energy product showed 9.23 MGOe.

• Journal of Powder Materials
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• v.23 no.6
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• pp.426-431
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• 2016

The Fe-Cr-Al alloy system shows an excellent heat resistance because of the formation of an $Al_2O_3$ film on the metal surface in an oxidizing atmosphere at high temperatures up to $1400^{\circ}C$. The Fecralloy needs an additive that can act as a binder because of its bad compactability. In this study, the green compacts of STS434L and Al powder added to Fecralloy are oxidized at $950^{\circ}C$ for up to 210 h. Fecralloy and Al is mixed by two types of ball milling. One is vented to air and the other was performed in a sealed jar. In the case of Al addition, there are no significant changes in the electrical resistance. Before the oxidation test, Al oxides are present in the Fecralloy surface, as determined from the energy dispersive spectroscopy results. The addition of Al improves the compactability because of an increased density, and the addition of STS434L increases the electrical resistivity by forming a composite oxide.

• Journal of Powder Materials
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• v.25 no.1
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• pp.25-29
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• 2018

Porous Cu with a dispersion of nanoscale $Al_2O_3$ particles is fabricated by freeze-drying $CuO-Al_2O_3$/camphene slurry and sintering. Camphene slurries with $CuO-Al_2O_3$ contents of 5 and 10 vol% are unidirectionally frozen at $-30^{\circ}C$, and pores are generated in the frozen specimens by camphene sublimation during air drying. The green bodies are sintered for 1 h at $700^{\circ}C$ and $800^{\circ}C$ in $H_2$ atmosphere. The sintered samples show large pores of $100{\mu}m$ in average size aligned parallel to the camphene growth direction. The internal walls of the large pores feature relatively small pores of ${\sim}10{\mu}m$ in size. The size of the large pores decreases with increasing $CuO-Al_2O_3$ content by the changing degree of powder rearrangement in the slurry. The size of the small pores decreases with increasing sintering temperature. Microstructural analysis reveals that 100-nm $Al_2O_3$ particles are homogeneously dispersed in the Cu matrix. These results suggest that a porous composite body with aligned large pores could be fabricated by a freeze-drying and $H_2$ reducing process.

• Journal of Integrative Natural Science
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• v.13 no.1
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• pp.27-33
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• 2020

The unsustainable human activities like increased use of automobiles, heavy industrialization and the use of large volumes of fertilizers, chemicals and pesticides in the agricultural land cause climate change problems in one way or another. Under normal circumstances, the heat radiations from the sun will be reflected back. An excessive volume of GHGs in the atmosphere would prevent these radiations from reflecting back. East Asia is facing severe climate change issues in recent times. A lot of climate change problems such as hurricanes and floods have been reported from this region in the last couple of decades. The study aimed at investigating the climate change in East Asia with changing Sea Surface Temperature (SST). The study adopted a quantitative research method with a case study research design where a deliberate focus was made on the East Asia Region. Secondary data was gathered and analyzed to yield both descriptive and inferential statistics. The study concluded that the impact of East Asia Climate variability was significant mainly for some extreme events. Also, the study concluded that there was a significant link between the change of the East Asia climate variability and that of the sea surface temperature. Further, the study concluded that a linear relationship existed between the sea surface temperature and the climate of East Asia. Hence, a linear regression was a significant predictor of the East Asia Climate (EAC) based on changing sea surface temperature. The model revealed that 37.4% of the variations in the climate change index were explained by the changes in the sea surface temperature. The climate was expected to change with a value of 49.48 for a unit change in the sea surface temperature.

• Journal of Adhesion and Interface
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• v.8 no.3
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• pp.16-23
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• 2007

Polyester fabrics and knits were corona treated with different current intensity (5, 10, 15, 20 A) and feeding speed (5, 10, 15 m/min). We confirmed the surface change of polyester fabrics and knits using scanning electron microscopy (SEM) and X-ray photoelectron spectrometer (XPS). And the change of physical properties through measuring the tensile strength, dry and wet bonding strength. Thermosetting reactive polyurethane hot melt adhesive was used in the adhesion of polyester fabrics and knits. Functional groups were introduced on PET fabrics and knits surface by treating the PET fabrics and knits in air atmosphere with corona discharge, and take placed unevenness, the result adhesion was improved. When consider both dry and wet bonding strength, we think that appropriate conditions in the PET fabrics corona treatment are feeding speed 10 m/min, current intensity 15 A and appropriate conditions in the mesh type PET knits corona treatment are feeding speed 10 m/min, current intensity above 10 A.

• Journal of Adhesion and Interface
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• v.17 no.3
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• pp.104-109
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• 2016

Compare AC corona and DC corona treatment effects, polyester fabrics were AC corona treated with different current intensity (5, 10, 15 A) and feeding speed (5, 10, 15 m/min) as the same DC corona treatment conditions of the preceding research. We confirmed the surface change of polyester fabrics using scanning electron microscopy (SEM) and X-ray photoelectron spectrometer (XPS), and the change of physical properties through measuring the dry and wet bonding strength. The surface changes of polyester fabrics by treating in air atmosphere with AC corona discharge are shown similar tendency with DC corona discharge. Generally dry bonding strength were increased with increasing current intensity and feeding speed, but wet bonding strength were increased with increasing current intensity and decreasing feeding speed in both AC and DC corona treatment. When the current is 20 A, carbonization occurs in DC corona discharge but carbonization does not occur in DC corona discharge.

• Bulletin of the Korean Chemical Society
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• v.30 no.5
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• pp.1135-1138
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• 2009

Hollow Sn and Pb nanoparticles have been prepared by a rapid injection of an aqueous solution of $SnCl_2$- poly(vinylpyrrolidone) (PVP, surfactant) and $Pb(OAc)_2${\cdot}$3H_2O-PVP$ into an aqueous solution of sodium borohydride (reducing agent) in simple, one-pot reaction at room temperature under an argon atmosphere, respectively. The two hollow nanoparticles have been fully characterized by TEM, HRTEM, SAED, XRD, and EDX analyses. Upon exposure to air, the black Pb hollow nanoparticles are gradually transformed into a mixture of Pb, litharge (tetragonal PbO), massicot (orthorhombic PbO), and $Pb_5O_8$. The order and speed of mixing of the reactants between the metal precursor-PVP and the reductant solutions and stoichiometry of all the reactants are crucial factors for the formation of the two hollow nanocrystals. The Sn and Pb hollow nanoparticles were produced only when 1:(1.5-2) and 1:3 ratios of the Sn and Pb precursors to $NaBH_4$ were employed with a rapid injection, respectively.

• Journal of Environmental Science International
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• v.24 no.6
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• pp.819-826
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• 2015

This study measured temperatures and albedos of urban surfaces for different colors and materials during summer, and calculated the energy budget over different urban surfaces to find out the thermal performance affecting the heat built-up. The study selected six surface colors and 13 materials common in urban landscape. Their surface temperatures (Ts) and albedos were measured at a given time interval in the daytime from June to August. Average Ts over summer season for asphalt-colored brick was $4.0^{\circ}C$ higher than that for light red-colored one and $9.7^{\circ}C$ higher than that for white-colored one. The Ts for artificial surface materials of asphalt paving, brown brick wall, and green concrete wall was $6.0^{\circ}C$ higher than that for natural and semi-natural ones of grass, grassy block, and planted concrete wall. There was the greatest difference of $16.3^{\circ}C$ at midafternoon in the Ts between asphalt paving and planted concrete wall. Average albedo over summer season of surface materials ranged from 0.08 for asphalt paving to 0.67 for white concrete wall. This difference in the albedo was associated with a maximum of $15.7^{\circ}C$ difference at midafternoon in the Ts. Increasing the albedo by 0.1 (from 0.22 to 0.32) reduced the Ts by about $1.3^{\circ}C$. Average storage heat at midday by natural and semi-natural surfaces of grass and grassy block was about 10% lower than that by artificial ones of asphalt, light-red brick, and concrete. Reflected radiation, which ultimately contributes to heating the urban atmosphere, was 3.7 times greater for light-red brick and concrete surfaces than for asphalt surface. Thus, surfaces with in-between tone and color are more effective than dark- or white-colored ones, and natural or semi-natural surfaces are much greater than artificial ones in improving the urban thermal environment. This study provides new information on correlation between Ts and air temperature, relationship between albedo and Ts, and the energy budget.

• The KSFM Journal of Fluid Machinery
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• v.13 no.1
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• pp.42-51
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• 2010

Many different types of fan have been applying to various industrial fields. Fan design methods are much different depending on the types of fan, operating conditions, and connecting parts at the inlet or exit of the fan etc. In this study, design methods for an axial-type suction fan are studied. This fan discharges the air in the relative static pressure of -285Pa to the atmosphere with the flow rate of $960m^3/min$. For three-dimensional blade design, three different design methods were applied, such as the free vortex method, the exponential method, and the cascade method. In the cascade method, the blade loading along the radial direction was obtained from the lift coefficient which was necessary to obtain the pressure rise on a fan rotor. This method is different from the free vortex and the exponential method which control the strength of the vortex. The fan performance prediction was conducted using the CFD with three different inlet ducts. The best fan performance was obtained when the fan was designed by using the cascade method. The designed fan using the exponential method showed better performance compared to a fan designed using the free vortex method. However, the fan performance was changed depending on the installed inlet ducts. So, an efficient fan can be designed with the adjustment of design variables on the basis of the flow structures within the fan as well as the fan design procedure.

• Journal of Technologic Dentistry
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• v.23 no.1
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• pp.55-64
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• 2001

This study is focusing on the improvement of problems of Ti-6Al-4V alloy. A new Ti based alloy, Ti-15Sn-4Nb, have designed to examine any possibility of improving the mechanical properties and biocompatibility. Specimens of Ti alloys were melted in vacuum arc furnace and homogenized at $100^{\circ}C$ for 24h. All specimens were solution treated at $812^{\circ}C$ and aged at $500^{\circ}C$ for 10h. The corrosion resistance of Ti alloys was evaluated by potentiodynamic polarization test and immersion test inl%Lactic acid solutions. Ti-15Sn-4Nb system alloys showed Widmanstatten microstructure after solution treatment which is typical microstructure of ${\alpha}+{\beta}$ type Ti alloys. Analysing the corrosion resistance of Ti alloys, it was concluded that the passive films of Ti-15Sn-4Nb system alloys are more stable than that of Ti-6Al-4V alloys. Also, the corrosion resistance of Ti-15Sn-4Nb system alloys was improved with adding elements, Hf. It was analysed that the passive film of the Ti-15Sn-4Nb alloy which was formed in air atmosphere was consisted of TiO2, SnO and NbO through X-ray photoelectron spectroscopy(XPS) analysis.