• Korean Journal of Materials Research
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• v.28 no.2
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• pp.95-100
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• 2018

In this study, $ZrO_2$ ceramic ink was formulated for additive manufacturing three dimensional structure using dispenser printing technique. Ceramic ink with various $ZrO_2$ loading (30, 40, 50vol%) was prepared to evaluate their rheological properties and printability. High $ZrO_2$ loading $ZrO_2$ ceramic ink showed higher elastic modulus and improved shape retention, when the ceramic ink was printed and sintered at $1450^{\circ}C$ for 1h. Microstructural analysis of printed $ZrO_2$ objective indicated that high $ZrO_2$ loading objective showed lower porosity and smaller pore size.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.7 no.3
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• pp.473-487
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• 1995

A loud speaker-driven zero-c.o.p. thermoacoustic refrigerator where an automotive catalytic converter is utilized as a stack has been fabricated and investigated experimentally. Without any heat exchangers at both ends of stack(and thus with zero c. o. p.), temperatures on the stack are measured and various heat transfer rates are calculated from the measured temperatures. Temperatures on the stack have been also calculated numerically using a finite difference method. The measured temperatures are in fair agreement with the calculated temperatures for lower frequency than 300Hz, however, the former deviates from the latter considerably for higher frequency. Two types of c. o. p. have been defined as appropriate to the experiment. While the nominal c. o. p. is zero(the condition in which the pumped heat flow rate in the pore exactly cancels the axial heat conduction down the stack), the true c. o. p. is found to be about 0.14 for 300Hz from the experiments.

• Bulletin of the Korean Chemical Society
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• v.31 no.11
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• pp.3163-3172
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• 2010

In this work, a novel method to synthesis of an acrylic superabsorbent hydrogel was reported. In the two stage hydrogel synthesis, first copolymerization reaction of acrylonitrile (AN) and acrylamide (AM) monomers using ammonium persulfate (APS) as a free radical initiator was performed. In the second stage, the resulted copolymer was hydrolyzed to produce carboxamide and carboxylate groups followed by in situ crosslinking of the polyacrylonitrile chains. The results from FTIR spectroscopy and the dark red-yellow color change show that the copolymerization, alkaline hydrolysis and crosslinking reactions have been do take place. Scanning electron microscopy (SEM) verifies that the synthesized hydrogels have a porous structure. The results of Brunauer-Emmett-Teller (BET) analysis showed that the average pore diameter of the synthesized hydrogel was 13.9 nm. The synthetic parameters affecting on swelling capacity of the hydrogel, such as AM/AN weight ratio and hydrolysis time and temperature, were systematically optimized to achieve maximum swelling capacity (330 g/g). The swollen gel strength of the synthesized hydrogels was evaluated via viscoelastic measurements. The results indicated that superabsorbent polymers with high water absorbency were accompanied by low gel strength. The swelling of superabsorbent hydrogels was also measured in various solutions with pH values ranging from 1 to 13. Also, the pH reversibility and on-off switching behavior makes the hydrogel as a good candidate for controlled delivery of bioactive agents. Finally, the swelling of synthesized hydrogels with various particle sizes obey second order kinetics.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.17 no.4
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• pp.451-458
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• 2004

The study was focused on the development of computational scheme in three dimensional configurations by applying effective heat capacity model to the numerical procedure in order to predict the temperature profiles of a buried pipeline and the frozen penetration depth(FPD) of a freezing soil medium. To realize this, the investigator conducted the unsteady state heat transfer analysis, using the commercial code ABAQUS, for the freezing granite soil medium including a pipeline in a closed system. The proposed model took into consideration the phase change effect of in situ pore water in the frozen fringe. The comparison of results obtained by the proposed model and the actual performances was valuable in establishing a level of confidence in the application of introduced theory.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2007.04a
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• pp.3-17
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• 2007

This paper provides an introduction to life-span simulation and numerical approach to support the performance design processes of reinforced concrete structures. An integrated computational system is proposed for life-span simulation of reinforced concrete. Conservation of moisture, carbon dioxide, oxygen, chloride, calcium and momentum is solved with hydration, carbonation, corrosion, ion dissolution. damage evolution and their thermodynamic/mechanical equilibrium. Coupled analysis of mass transport and damage mechanics associated with steel corrosion is presented for structural performance assessment of reinforced concrete. Multi-scale modeling of micro-pore formation and transport phenomena of moisture and ions are mutually linked for predicting the corrosion of reinforcement and volumetric changes. The interaction of crack propagation with corroded gel migration can also be simulated. Two finite element codes. multi-chemo physical simulation code (DuCOM) and nonlinear dynamic code of structural reinforced concrete (COM3) were combined together to form the integrated simulation system. This computational system was verified by the laboratory scale and large scale experiments of damaged reinforced concrete members under static loads, and has been applied to safety and serviceability assessment of existing structures. Based on the damage details predicted by the nonlinear finite element analytical system, the life-span-cost of RC structures including the original construction costs and the repairing costs for possible damage during the service life can be evaluated for design purpose.

• Journal of Environmental Science International
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• v.22 no.7
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• pp.837-845
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• 2013

This study was designed to synthesize mesoporous carbon, porous carbonic material and to characterize its surface in an attempt to adsorption methane gas($CH_4$). Synthesis of mesoporous carbon was carried out under two steps ; 1. forming a RF-silica complex with a mold using CTMABr, a surfactant, and TEOS, raw material of silica, and 2. eliminating silica through carbonization and HF treatment. The mesoporous carbon was synthesized under various conditions of synthesis time and calcination. Eight different types of mesoporous carbon, which were designated as MC1, MC2, MC3, MC4, MCT1, MCT2, MCT3, and MCT4, were prepared depending upon preparation conditions. The analysis of mesoporous carbon characteristics showed that the calcination of silica stabilized the mixed structure of silica and carbonic complex, and made the particle uniform. The results also showed that hydrothermal synthesis time did not have a strong influence on the size of pore. The bigger specific surface area was obtained as the hydrothermal synthesis time was extended. However, the specific surface area was getting smaller again after a certain period of time. In adsorption experiments, $CH_4$ was used as adsorbate. For the case of $CH_4$, MCT3 showed the highest adsorption efficiency.

• Journal of Periodontal and Implant Science
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• v.34 no.3
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• pp.683-698
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• 2004

One of the bone substitutes now in routine use, deproteinized bovine bone mineral(DBBM), is regarded as resorbable and osteoconductive, but some studies refute this. The present study was performed to evaluate the effects of DBBM on guided bone regeneration using titanium membrane on the calvaria of rabbit. At 2 weeks, 4 weeks, 8 weeks, and 12 weeks after surgery, the animal was scrificed. Non-decalcified specimens were produced for histologic analysis. The results of this study were as follows : 1. Titanium membrane was biocompatible and capable of space-maintaining, but there was ingrowth of soft tissue through the pore of titanium membrane. 2. There was no resorption or reduction of DBBM with time. 3. Some of the DBBM particles were combined with newly formed bone. But, apart from host bone, a great part of the particles were surrounded by connective tissue. 4. The bone formation was slight vertically and restricted to superficial area of host bone. Whithin the above results, DBBM dose not appear to contribute to bone formation. DBBM may disturb the migration and proliferation of mesenchymal cell derived from host bone and increase the growth of connective tissue. Therefore, careful caution is needed on selection of bone graft material and surgical protocol at guided bone regeneration for implant placement.

• Journal of Ocean Engineering and Technology
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• v.30 no.6
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• pp.484-497
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• 2016

In order to understand the characteristics of the topography change in front of an impermeable breakwater, a coupled model for a two-way analysis of the existing LES-WASS-2D and newly developed morphodynamic model was suggested. A comparison to existing experimental results revealed that the results computed using the 2-D hydro-morphodynamic model were in good agreement with the experimental results for the wave form, pore water pressure in the seabed, and topographical change in front of a submerged breakwater. It was shown that the two-way model suggested in this study is applicable to a morphological change in the seabed around a submerged breakwater. Then, using the numerical results, the topographical changes in front of an impermeable submerged breakwater were examined in relation to partial standing waves. Moreover, the characteristics of the local scour depths in front of them are also discussed in relation to incident wave conditions, sediment qualities, and submerged breakwater shapes.

• Carbon letters
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• v.7 no.1
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• pp.34-41
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• 2006

The objective of this paper is to compare the variation of surface properties by hydrochloric acid pre-treatment and of metallic potassium and their salts loading effect for activated carbon after surfaces transformation by acid. From the results of nitrogen adsorption, each isotherm shows a distinct knee band, which is closely related to the characteristic of microporous carbons with capillary condensation in micropores. In order to present the causes of the differences in surface properties and $S_{BET}$ after the samples were treated with hydrochloric acid, pore structure and surface morphology are investigated by adsorption analysis. X-ray diffraction (XRD) patterns indicate that activated carbons show better performance for metallic potassium and potassium salts by pre-treatment with hydrochloric acid. Scanning electron microscopy (SEM) pictures of potassium/activated carbon particles provide information about the homogeneous distribution of metal or metal complex on the surface. For the chemical composition microanalysis for potassium treatment of the activated carbon pre-treated with hydrochloric acid, samples were analyzed by energy disperse X-ray (EDX). Finally, the type and quality of oxygen groups are determined from the method proposed by Boehm. A positive influence of the acidic groups on the carbon surface by acid treatment is also demonstrated by an increase in the contents of potassium salts with increasing of acidic groups calculated from Boehm titration.

• Journal of the Korean Ceramic Society
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• v.43 no.12 s.295
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• pp.788-797
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• 2006

An anode-supported SOFC single cell having $5{\mu}m$ thin electrolyte was fabricated cost-effectively by tape casting, laminating, and co-filing of anode (NiO-YSZ), cathode (LSM-YSZ), and electrolyte (YSZ) components. The optimal slurry compositions of the green tapes for SOFC components were determined by an analysis of the mean diameter, the slurry viscosity, the tensile strength/strain of the green tapes, and their green microstructures. The single cells with a dense electrolyte and porous electrodes could be co-fired successfully at $1325\sim1350^{\circ}C$ by controlling the contents of pore former and the ratio of coarse YSZ and fine YSZ in the anode and the cathode. The single cell co-fired at $1350^{\circ}C$ showed $100.2mWcm^{-2}$ of maximum power density at $800^{\circ}C$ but it was impossible to apply it to operate at low temperature because of low performance and high ASR, which were attributed to formation of the secondary phases in the cathode and the interface between the electrolyte and the cathode.