• Journal of the Korean Ceramic Society
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• v.41 no.3
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• pp.210-215
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• 2004

Porous ceramics for water-permeable paving brick was prepared by the sintering of mixed materials comprising of sewage sludge ash, waste porcelain fragment, waste glaze and low-grade clay at 1,000$^{\circ}C$ for 2 h, and the physical $.$mechanical properties, the permeability and the freeze-thaw resistance of specimens with preparation parameters were investigated. The physical mechanical properties were increased in specimens while porosity and permeability were decreased with increasing sewage sludge ash content and sintering temperature on the properties of specimens showed the opposite results. The bulk density, porosity, compressive strength and permeability (passed charge) of 30A60F specimens with 30 wt% of sewage sludge ash content, waste porcelain fragment size with 1∼2 mm and sintered at 1,000$^{\circ}C$ for 2 h were 2.17, 46.2%, 221 kgf/$\textrm{cm}^2$ and 3,150 coulombs, respectively. The permeability was increased with increasing waste porcelain fragment size, however compressive strength was decreased. The freeze-thaw resistance of 30A60F specimen with 1∼2 mm of fragment size was superior to that of the other specimens. The 30A60F specimens can be used for the water-permeable paving brick with the high permeability and adequate strength. The heavy metals included in the all specimens showed lower than the standard level.

• Journal of the Korean earth science society
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• v.22 no.1
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• pp.40-46
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• 2001

Heat exchange between the atmosphere and sea is produced using the data from two 3m discus buoy installed by KMA in 1996. The meteorological and oceanic characteristics at the Dukjukdo and Chilbaldo buoy for the period 1996 ${\sim}$ 2000 are discussed. Daily averaged sensible heat and latent heat flux at each site are estimated from bulk aerodynamic method using given data and analyzed. Quantitative analyses show SST indicates 1-year cycle like air temperature but has 1 month lag. Sea level pressure is lowest in July, humidity is higher from May to August, and wind speed has averaged value of 5 m/s and higher in autumn and winter. Sensible heat flux analyses present that strong heat loss from the sea occurs in autumn and winter and weak heat loss from atmosphere appears in spring and summer, and net sensible heat loss from the sea is found throughout the year. The ocean significantly releases latent heat into atmosphere from August to May but get a little latent heat from atmosphere in other months. Net latent heat loss from the sea is larger than net sensible heat loss except in January and February. Comparison with two sites suggests that the magnitude of heat flux and their fluctuation are generally stronger at Dukjukdo than at Chilbaldo. In case study, both sensible and latent heat flux is a little more at Chilbaldo in March 1998, but substantially stronger at Dukjukdo in November 1996.

• Journal of the Korean Society of Food Science and Nutrition
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• v.21 no.5
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• pp.525-533
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• 1992

To improve the food quality of traditional Jeung-pyun(Korean fermenfed rice cake), effect of mixed ingredients on the quality of protein enriched product was studied. Changes were evaluated in chemical and textural properties of protein enriched Jeung-pyun altered by fermentation time, temperature, and steaming time. The maximum volume wxpansion was noted in dough mixed with rice flour(100 g), soy flour(25 g), sucrose(20 g), Tak-ju(50 ml) and water(10 ml), and then fermented at $35^{\circ}C$ for 3 hours. Soy protein isolate(SPI) enriched rice dough had a maximum expanded volume when 15g(w/w) of SPI, 20g(w/w) of sucrose, 60ml(v/w) of Tak-ju and 50ml(v/w) of water added into 100g rice flour, and then fermented at $30^{\circ}C$ for 2 hours. Steaming after fermentation made the smaller volume of bulk $45^{\circ}C$-50% of the initial volume be showed just after fermentation. Protein enriched Jeung-pyun prepared under the maximal volume endowing conditions showed the best protein quality(protein digestibility and protein efficiency ratio) and starch structure which was susceptible towards enzyme reaction. The improved starch quality of protein enriched Jeung-pyun could be confirmed by reducing power, gelatinization degree and amylose content. Jeung-pyun riched with soy flour at 20% level or with SPI at 5% showed the best overall quality by sensory and textural property but it had a problem in browning.

• Journal of Advanced Marine Engineering and Technology
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• v.40 no.6
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• pp.493-498
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• 2016

In the present study, graphene oxide based polyurethane foams were manufactured as a part of the development process of mechanically strengthened polyurethane foam insulation material. This material is used in a liquefied natural gas carrier cargo containment system. The temperature of the containment system is $-163^{\circ}C$. First, graphene oxide was synthesized using the Hummers' method, and it was supplemented into polyol-isocyanate reagent by considering a different amount of graphene oxide weight percent. Then, a bulk form of graphene-oxide-polyurethane foam was manufactured. In order to investigate the cell stability of the graphene-oxide-polyurethane foam, its microstructural morphology was observed, and the effect of graphene oxide on microstructure of the polyurethane foam was investigated. In addition, the compressive strength of graphene-oxide-polyurethane foam was measured at ambient and cryogenic temperatures. The cryogenic tests were conducted in a cryogenic chamber equipped with universal testing machine to investigate mechanical and failure characteristics of the graphene-oxide-polyurethane foam. The results revealed that the additions of graphene oxide enhanced the mechanical characteristics of polyurethane foam. However, cell stability and mechanical strength of graphene-oxide-polyurethane foam decreased as the weight percent of graphene oxide was increased.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.490.2-490.2
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• 2014

Since the general solar cells accept sun light at the front side, excluding the electrode area, electrons move from the emitter to the front electrode and start to collect at the grid edge. Thus the edge of gridline can be important for electrical properties of screen-printed silicon solar cells. In this study, the improvement of electrical properties in screen-printed crystalline silicon solar cells by contact treatment of grid edge was investigated. The samples with $60{\Omega}/{\square}$ and $70{\Omega}/{\square}$ emitter were prepared. After front side of samples was deposited by SiNx commercial Ag paste and Al paste were printed at front side and rear side respectively. Each sample was co-fired between $670^{\circ}C$ and $780^{\circ}C$ in the rapid thermal processing (RTP). After the firing process, the cells were dipped in 2.5% hydrofluoric acid (HF) at room temperature for various times under 60 seconds and then rinsed in deionized water. (This is called "contact treatment") After dipping in HF for a certain period, the samples from each firing condition were compared by measurement. Cell performances were measured by Suns-Voc, solar simulator, the transfer length method and a field emission scanning electron microscope. According to HF treatment, once the thin glass layer at the grid edge was etched, the current transport was changed from tunneling via Ag colloids in the glass layer to direct transport via Ag colloids between the Ag bulk and the emitter. Thus, the transfer length as well as the specific contact resistance decreased. For more details a model of the current path was proposed to explain the effect of HF treatment at the edge of the Ag grid. It is expected that HF treatment may help to improve the contact of high sheet-resistance emitter as well as the contact of a high specific contact resistance.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 1999.04a
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• pp.5-5
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• 1999

The Principal deficiency of the existing notion about the sintering-mixtures consists in the fact that almost no attention is focused on the Phenomenon of alloy formation during sintering, its connection with dimensional changes of powder bodies, and no correct ideas on the driving force for the sintering process in the stage of establishing chemical equilibrium in a system are available as well. Another disadvantage of the classical sintering theory is an erroneous conception on the dissolution mechanism of solid in liquid. The two-particle model widely used in the literature to describe the sintering phenomenon in solid state disregards the nature of the neighbouring surrounding particles, the presence of pores between them, and the rise of so called arch effect. In this presentation, new basic scientific principles of the driving forces for the sintering process of a two-component powder body, of a diffusion mechanism of the interaction between solid and liquid phases, of stresses and deformation arising in the diffusion zone have been developed. The major driving force for sintering the mixture from components capable of forming solid solutions and intermetallic compounds is attributed to the alloy formation rather than the reduction of the free surface area until the chemical equilibrium is achieved in a system. The lecture considers a multiparticle model of the mixed powder-body and the nature of its volume changes during solid-state and liquid-phase sintering. It explains the discovered S-and V-type concentration dependencies of the change in the compact volume during solid-state sintering. It is supposed in the literature that the dissolution of solid in liquid is realised due to the removal of atoms from the surface of the solid phase into the melt and then their diffusicn transfer from the solid-liquid interface into the bulk of liquid. It has been shown in our experimental studies that the mechanism of the interaction between two components, one of them being liquid, consist in diffusion of the solvent atoms from the liquid into the solid phase until the concentration of solid solutions or an intermetallic compound in the surface layer enables them to pass into the liquid by means of melting. The lecture discusses peculimities of liquid phase formation in systems with intermediate compounds and the role of the liquid phase in bringing about the exothermic effect. At the frist stage of liquid phase sintering the diffusion of atoms from the melt into the solid causes the powder body to grow. At the second stage the diminution of particles in size as a result of their dissolution in the liquid draws their centres closer to each other and makes the compact to shrink Analytical equations were derived to describe quantitatively the porosity and volume changes of compacts as a result of alloy formation during liquid phase sinteIing. Selection criteria for an additive, its concentration and the temperature regime of sintering to control the density the structure of sintered alloys are given.

• Nuclear Engineering and Technology
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• v.45 no.5
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• pp.605-612
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• 2013

Removal of decay heat from an operating reactor during a prolonged station blackout condition is a big concern for reactor designers, especially after the recent Fukushima accident. In the case of a prolonged station blackout condition, heat removal is possible only by passive means since no pumps or active systems are available. Keeping this in mind, the AHWR has been designed with many passive safety features. One of them is a passive means of removing decay heat with the help of Isolation Condensers (ICs) which are submerged in a big water pool called the Gravity Driven Water Pool (GDWP). The ICs have many tubes in which the steam, generated by the reactor core due to the decay heat, flows and condenses by rejecting the heat into the water pool. After condensation, the condensate falls back into the steam drum of the reactor. The GDWP tank holds a large amount of water, about 8000 $m^3$, which is located at a higher elevation than the steam drum of the reactor in order to promote natural circulation. Due to the recent Fukushima type accidents, it has been a concern to understand and evaluate the capability of the ICs to remove decay heat for a prolonged period without escalating fuel sheath temperature. In view of this, an analysis has been performed for decay heat removal characteristics over several days of an AHWR by ICs. The computer code RELAP5/MOD3.2 was used for this purpose. Results indicate that the ICs can remove the decay heat for more than 10 days without causing any bulk boiling in the GDWP. After that, decay heat can be removed for more than 40 days by boiling off the pool inventory. The pressure inside the containment does not exceed the design pressure even after 10 days by condensation of steam generated from the GDWP on the walls of containment and on the Passive Containment Cooling System (PCCS) tubes. If venting is carried out after this period, the decay heat can be removed for more than 50 days without exceeding the design limits.

• Journal of the Korean Magnetics Society
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• v.22 no.3
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• pp.79-84
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• 2012

Nano-magnetic materials such as iron-nitrides have been actively studied as an alternative to the application of high density, high performance needs for next generation information storage and also alternative to the rare earth and neodymium magnet. $Fe_4N$ is the basic materials for magnetic storage media and is one of the important magnetic materials in focus because of its higher magnetic recording density and chemical stability. Single phase ${\gamma}^{\prime}-Fe_4N$ nanoparticles have been prepared by a PAD (Plasma Arc Discharge) method and nitriding in a $NH_3-H_2$ mixed gases at temperature, $400^{\circ}C$ for 4 hrs. Also $Fe_{17}Sm_2N_x$ powders were synthesized by nitriding after reduction/diffusion of $Fe_{17}Sm_2$ to compare the magnetic properties with nano-sized $Fe_4N$ particles. The saturation magnetization of $Fe_4N$ and $Fe_{17}Sm_2N_x$ were 149 and 117 emu/g, respectively, but the coercive force was considerably smaller than that of bulk or acicular $Fe_4N$.

• Journal of Korean Society of Environmental Engineers
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• v.27 no.7
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• pp.771-776
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• 2005

In recent days, there is much interest in the biocidal activity of silver since silver is known to be safe and effective as disinfectant and biocidal material against coliforms and viruses. In particular, nano silted silver particles which can be used as effective biocidal material received more attention. Accordingly, it is important to investigate antimicrobial activity and mechanism of nano sized silver particles prepared in a cost-effective manner. In this study, nano sized silver particles were prepared via photoreduction of a silver salt ($AgNO_3$) in the bulk phase of $PEO_{20}-PPO_{70}-PEO_{20}$ (Pluronic 123) block copolymer The antimicrobial efficacy of silver nano particles against E. coli was investigated and compared with that of silver ion as the concentration of silver nano particles, pH ($5.6{\sim}8.2$), temperature ($4^{\circ}C{\sim}35^{\circ}C$) varied in aqueous system. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) was used to examine the nature of damaged microorganism with nano sized silver particles and silver ion. This study showed that antimicrobial efficacy of silver nano particles was approximately one twentieth than that of silver ion. It was more biocidal at higher pH in contrast with silver ion. In addition, nano silver particles was demonstrated to disrupt the outer membrane of E. coli, subsequently causing their aggregation. On the other hand, silver ion diffused into the cell damaging the cytoplasmic membrane without disrupting the outer membrane of E. coli.

• Journal of the Korean Society of Food Science and Nutrition
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• v.21 no.1
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• pp.101-108
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• 1992

Changes were evaluated in chemical and textural properties of Jeung-pyun (fermented rice cake) altered by the particle size of rice flour, amount of added Tak-ju (Korean traditional unrefined liquor) and sucrose, fermentation time and temperature, and steaming time. Particle size of polished rice flour did not affect the volume expansion during fermentation of rice dough by Tak-ju. The maximum expanded volume was noted in the dough, containing 20% sucrose (rice flour vs sucrose = 5 : 1, w/w), fermented at $35^{\circ}C$ for 3 hours. Any volume expansion was not occurred in rice dough without sucrose. The highest value of reducing power and gelatinization degree were observed in the rice dough with Tak-ju (rice flour vs Tak-ju = 2 : 1, w/v), while the lowest blue value was revealed in that case. Steaming followed after fermentation made the smaller volume of bulk by $45{\sim}50%$ of the initial volume be showed just after fermentation. Jeung-pyun prepared under the conditions could give maximum expanded volume by fermentation showed the best overall quality by sensory and textual properties.