• Membrane Journal
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• v.34 no.1
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• pp.58-69
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• 2024

Reverse electrodialysis (RED) is an electro-membrane process employing ion-exchange membranes (IEMs) that can harvest electric energy from the concentration difference between seawater and river water. Multivalent ions contained in seawater and river water bind strongly to the fixed charge groups of the IEM, causing high resistance and reducing open-circuit voltage and power density through uphill transport. In this study, a pore-filled anion-exchange membrane (PFAEM) with excellent monovalent ion selectivity and electrochemical properties was fabricated and characterized for RED application. The monovalent ion selectivity of the prepared membrane was 3.65, which was superior to a commercial membrane (ASE, Astom Corp.) with a selectivity of 1.27 under the same conditions. Additionally, the prepared membrane showed excellent electrochemical properties, including low electrical resistance compared to ASE. As a result of evaluating RED performance under seawater of 0.459 M NaCl/0.0510 M Na₂SO₄ and river water of 0.0153 M NaCl/0.0017 M Na₂SO₄, the maximum power density of 1.80 W/m² was obtained by applying the prepared membrane, which is a 40.6% improved output performance compared to the ASE membrane.

• Journal of the Korean Ceramic Society
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• v.56 no.4
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• pp.350-353
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• 2019

Porous alumina ceramics with addition of 0, 5, 10, 15, and 20 wt% Al(H₂PO₄)₃ were sintered at 1300, 1350, and 1400℃. The effects of the Al(H₂PO₄)₃ addition on crystal phases, water absorption, open porosity, pore size distribution, microstructures, and flexural strength were studied extensively. The experimental results revealed that only characteristic peaks of corundum were indexed in the XRD patterns of the as-prepared porous ceramics. The water absorption and open porosity of the porous Al₂O₃ ceramics increased remarkably with an increase in Al(H₂PO₄)₃ addition. The flexural strength first increased to a maximum value when 5 wt% Al(H₂PO₄)₃ was added and then decreased as additional Al(H₂PO₄)₃ was further added. SEM images showed that the average Al₂O₃ grain size in the porous ceramics changed in an opposite way as the flexural strength. The porous Al₂O₃ ceramics with 10 wt% Al(H₂PO₄)₃ addition exhibited comparable flexural strength to the ceramics without Al(H₂PO₄)₃ addition, although the latter had much higher porosity.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.658-658
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• 2013

Graphene is an attractive material for various device applications due to great electrical properties and chemical properties. However, lack of band gap is significant hurdle of graphene for future electrical device applications. In the past few years, several methods have been attempted to open and tune a band gap of graphene. For example, researchers try to fabricate graphene nanoribbon (GNR) using various templates or unzip the carbon nanotubes itself. However, these methods generate small driving currents or transconductances because of the large amount of scattering source at edge of GNRs. At 2009, Bai et al. introduced graphene nanomesh (GNM) structures which can open the band gap of large area graphene at room temperature with high current. However, this method is complex and only small area is possible. For practical applications, it needs more simple and large scale process. Herein, we introduce a photosensitive graphene device fabrication using CdSe QD coated nano-porous graphene (NPG). In our experiment, NPG was fabricated by thin film anodic aluminum oxide (AAO) film as an etching mask. First of all, we transfer the AAO on the graphene. And then, we etch the graphene using O2 reactive ion etching (RIE). Finally, we fabricate graphene device thorough photolithography process. We can control the length of NPG neckwidth from AAO pore widening time and RIE etching time. And we can increase size of NPG as large as 2 $cm^2$. Thin CdSe QD layer was deposited by spin coatingprocess. We carried out NPG structure by using field emission scanning electron microscopy (FE-SEM). And device measurements were done by Keithley 4200 SCS with 532 nm laser beam (5 mW) irradiation.

• Membrane Journal
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• v.27 no.6
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• pp.469-476
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• 2017

Membrane separation is a technology of low energy consumption. Membranes made of zeolites are of great interest because their fixed and open pores in the size of small molecules inside crystalline structures allow separation processes under harsh conditions. While zeolite NaA (LTA-type) is industrially used for dewatering of organic solvents, its pore size and thermal and hydrothermal stability can be tuned by exchange of framework and extra-framework elements. SOD with pores of only 0.28 nm is of great interest for $H_2$- und $H_2O$-separation and also can be tuned by ion exchange. Zeolites open the opportunity to create membranes of adapted separation behavior for small molecules in conditions of surrounding technical processes.

• Korean Journal of Materials Research
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• v.34 no.1
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• pp.12-20
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• 2024

This study successfully prepared high-porosity aluminosilicate fibrous porous ceramics through vacuum suction filtration using aluminosilicate fiber as the primary raw material and glass powder as binder, with the appropriate incorporation of glass fiber. The effects of the composition of raw materials and sintering process on the structure and properties of the material were studied. The results show that when the content of glass powder reached 20 wt% and the samples were sintered at the temperature of 1,000 ℃, strong bonds were formed between the binder phase and fibers, resulting in a compressive strength of 0.63 MPa. When the sintering temperatures were increased from 1,000 ℃ to 1,200, the open porosity of the samples decreased from 89.08 % to 82.38 %, while the linear shrinkage increased from 1.13 % to 10.17 %. Meanwhile, during the sintering process, a large amount of cristobalite and mullite were precipitated from the aluminosilicate fibers, which reduced the performance of the aluminosilicate fibers and hindered the comprehensive improvement in sample performance. Based on these conditions, after adding 30 wt% glass fiber and being sintered at 1,000 ℃, the sample exhibited higher compressive strength (1.34 MPa), higher open porosity (89.13 %), and lower linear shrinkage (5.26 %). The aluminosilicate fibrous porous ceramic samples exhibited excellent permeability performance due to their high porosity and interconnected three-dimensional pore structures. When the samples were filtered at a flow rate of 150 mL/min, the measured pressure drop and permeability were 0.56 KPa and 0.77 × 10^-6 m² respectively.

• Journal of the Korean Ceramic Society
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• v.53 no.1
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• pp.43-49
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• 2016

This analyzed a Young's modulus (E), a thermal expansion coefficient (TEC, ${\beta}$) and a thermal conductivity (${\kappa}$) of the material with simple cubic particulate inclusion using two model structures: a parallel structure and a series structure of laminated layers. The derived ${\beta}$ equations were applied to calculate the ${\beta}$ value of the W-MgO system. The accuracy was higher for the series model structure than for the parallel model structure. Young's moduli ($E_c$) of sintered porous alumina compacts were theoretically related to the development of neck growth of grain boundary between sintered two particles and expressed as a function of porosity. The series structure model with cubic pores explained well the increased tendency of $E_c$ with neck growth rather than the parallel structure model. The thermal conductivity of the three phase system of alumina-mullite-pore was calculated by a theoretical equation developed in this research group, and compared with the experimental results. The pores in the sintered composite were treated as one phase. The measured thermal conductivity of the composite with 0.5-25% porosity (open and closed pores) was in accordance with the theoretical prediction based on the parallel structure model.

• 한국신재생에너지학회:학술대회논문집
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• 2010.06a
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• pp.95.2-95.2
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• 2010

염료감응형 태양전지의 효율을 향상을 시키기 위하여, 이산화티타니아박막을 doctor-blade 방법으로 FTO 기판위에 15-16um 코팅을 한뒤, 다른 온도의 $400^{\circ}C-600^{\circ}C$ 범위에서, 소결을 하였다. 상대전극은 FTO 기판위에 5Ml의 Pt용액을 가지고, $450^{\circ}C$온도에서 제작을 하였다. 실험의 결과 이산화티타니아의 표면거칠기 및 입자사이즈의 소결의 형상에 따라 DSSC의 효율의 상관관계가 영향을 받았다. 표면의 형상은 AFM으로 측정을 하였으며, 표면의 단차가 RMS의 값이 7nm이하 일 때, 효율의 향상을 이루었다. 실험결과 $500^{\circ}C$ 이하일 때, 상대적으로 낮은 open circuit voltage를 이루었으며, 낮은 Fill-factor를 이루었다. $500^{\circ}C$이상의 온도에서는 상대적으로 높은 high circuit voltage와 높은 fill factor를 나타내었다. 실험결과 $500^{\circ}C$에서 소결된 전극을 가진 DSSC가 단락의 전압과 개방전류가 상호보완된 적정값을 가져 가장 개선된 FF와 Eff를 나타내었다. 이와 같은 특성은 이산화티타니아의 준위 모식도에서 설명이 될수 있고, 이산화티타니아의 최적의 necking 및 pore, 입자크기등이 제어될수 있음을 의미한다.

• Journal of Applied Reliability
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• v.16 no.2
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• pp.104-109
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• 2016

Purpose: The purpose of this study is to analyze fracture behavior and failure mechanism of porous titanium for dental implant fabricated by space holder process. Method: Three porous titanium specimens with a specific volume fraction of open pore were test by 3 point bending and compression stress condition, respectively. Fracture appearance was observed by scanning electron microscope and discussed in relation with oxygen content. Results: For compression-tested specimens, two specimen showed brittle failure, while the other one showed normal failure after deformation. High oxygen content was detected in the brittle-fractured specimen. Several micro-cracks initiated at the struts propagated down to the bottom of the specimen resulting in normal failure. Conclusion: Oxygen contamination during the fabrication process can leads brittle premature failure, and hence quality problem of the porous titanium for dental implant.

• Proceedings of the Korean Institute of Resources Recycling Conference
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• 2001.05b
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• pp.129-132
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• 2001

The purpose of this research was to understand possibility of foodwaste treatment by hybrid anaerobic reactor(HAR). The Possibility of methane utility and applicability of hybrid reactor system using foodwaste as substrate was investigated. The maximum loading rate and optimized operational conditions were determined. Hybrid anaerobic reactor was filled with packing material 50% of its total volume between the tube and the outer surface. The packing material used was randomly packed open-pore synthesis activated ceramic(SAC) media as support media for microbial attachment, growth, and chemical stability protected bacteria from effect of organic acid accumulation. In this research, although foodwaste has high concentrations C $l^{[-10]}$ and S $O_{4}$$^{2-}$ concentration the possibility of foodwaste anaerobic treatment was when foodwaste is treated by anaerobic digestion, this study focused on the possibility using C $H_4$ gas made under the anaerobic treatment as an alternative energy source. Other objective of this research is to study struvite formation and crystal forms in anaerobic digester. HAR is used to investigate phosphate crystallization without the addition of chemicals.

• Corrosion Science and Technology
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• v.3 no.3
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• pp.118-126
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• 2004

The correlation between sensor output and corrosion rate of reinforcing steel was evaluated by laboratory electrochemical tests in saturated $Ca(OH)_2$ with 3.5 wt.% NaCl and confirmed in concrete environment. In this paper, two types of electrochemical probes were developed: galvanic cells containing of steel/copper and steel/stainless steel couples. Potentiodynamic test, weight loss measurement, monitoring of open-circuit potential, linear polarization resistance (LPR) measurement and electrochemical impedance spectroscopy (EIS) were used to evaluate the corrosion behavior of steel bar embedded in concrete. Also, galvanic current measurements were conducted to obtain the charge of sensor embedded in concrete. In this study, steel/copper and steel/stainless steel sensors showed a good correlation in simulated concrete solution between sensor output and corrosion rate of steel bar. However, there was no linear relationship between steel/stainless steel sensor output and corrosion rate of steel bar in concrete environment due to the low galvanic current output. Thus, steel/copper sensor is a reliable corrosion monitoring sensor system which can detect corrosion rate of reinforcing steel in concrete structures.