본 연구에서는 분리막 생물반응기(membrane bioreactor, MBR)에서 발생되는 생물막오염 완화에 탁월한 효과를 가진 분리막을 개발할 목적으로, 친수성 산소 기능기가 많은 탄소나노구체(carbon nanosphere, CNS)를 합성한 뒤, 이를 첨가 제로 활용하여 친수성과 다공성 기공 구조를 갖는 고성능 한외여과막을 제조하였다. CNS는 막 표면에 초승달 모양의 기공을 형성하였고, CNS 함량을 4.6 wt%까지 증가시킴에 따라 최대기공 크기보다 큰 결함을 야기하지 않으면서 평균 표면 기공 크 기를 약 40% 증가시키는 것으로 나타났다. 또한, CNS 복합막의 다공성 기공 구조는 CNS의 등방성 형태와 상대적으로 낮은 입자 수밀도 덕분에 CNS 첨가에 따른 고분자 용액의 점도 급등이 방지됐기 때문이라고 판단된다. 그러나 너무 다공성이 커 지게 되면 기계적 물성이 저하되므로, 기공구조와 기계적 성질을 포함한 종합적인 고려를 했을 때 CNS2.3이 가장 우수하다 고 관측되었다. CNS2.3은 CNS0에 비해 수투과도가 2배 이상 높을 뿐만 아니라, MBR 공정에서 분리막 세정이 요구될 때까 지의 운전 시간도 5배 이상 연장시킨 것으로 확인되었다.

In this study, the effects of kaolin addition on the properties of reticulated porous diatomite-kaolin composites are investigated. A reticulated porous diatomite-kaolin composite is prepared using the replica template method. The microstructure and pore characteristics of the reticulated porous diatomite-kaolin composites are analyzed by controlling the PPI value (45, 60, and 80 PPI) of the polyurethane foam (which are used as the polymer template), the ball-milling time (8 and 24 h), and the amount of kaolin (0–50 wt. %). The average pore size decreases as the amount of kaolin increases in the reticulated porous diatomite-kaolin composite. As the amount of kaolin increases, it can be determined that the amount of inter-connected pore channels is reduced because the plate-shaped kaolin particles connect the gaps between irregular diatomite particles. Consequently, a higher kaolin percentage affects the overall mechanical properties by improving the pore channel connectivity. The effect of kaolin addition on the basic properties of the reticulated porous diatomite-kaolin composite is further discussed with characterization data such as pore size distribution, scanning electron microscopy images, and compressive strength.

During a long-term operation of polymer electrolyte membrane fuel cells(PEMFCs), the fuel cell performance may degrade due to severe agglomeration and dissolution of metal nanoparticles in the cathode. To enhance the electrochemical durability of metal catalysts and to prevent the particle agglomeration in PEMFC operation, this paper proposes a hybrid catalyst structure composed of PtCo alloy nanoparticles encapsulated by porous carbon layers. In the hybrid catalyst structure, the dissolution and migration of PtCo nanoparticles can be effectively prevented by protective carbon shells. In addition, O2 can properly penetrate the porous carbon layers and react on the active Pt surface, which ensures high catalytic activity for the oxygen reduction reaction. Although the hybrid catalyst has a much smaller active surface area due to the carbon encapsulation compared to a commercial Pt catalyst without a carbon layer, it has a much higher specific activity and significantly improved durability than the Pt catalyst. Therefore, it is expected that the designed hybrid catalyst concept will provide an interesting strategy for development of high-performance fuel cell catalysts.

In this study, a numerical approach based on mid-point integrated finite elements and a viscous boundary is proposed for time-domain wave-propagation analyses in infinite poroelastic media. The proposed approach is accurate, efficient, and easy to implement in time-domain analyses. In the approach, an infinite domain is truncated at some distance. The truncated domain is represented by mid-point integrated finite elements with real element-lengths and a viscous boundary is attached to the end of the domain. Given that the dynamic behaviors of the proposed model can be expressed in terms of mass, damping, and stiffness matrices only, it can be implemented easily in the displacement-based finite-element formulation. No convolutional operations are required for time-domain calculations because the coefficient matrices are constant. The proposed numerical approach is applied to typical wave-propagation and soil-structure interaction problems. The model is verified to produce accurate and stable results. It is demonstrated that the numerical approach can be applied successfully to nonlinear soil-structure interaction problems.

Plasticization is one of the biggest challenges in gas separation polymeric membranes. Mixed matrix membrane (MMM) comprising inorganic nanofiller is the most promising solution for anti-plasticization, however, it requires large amount of nanofillers to achieve desired performance. We adopted 2-D nanocomposite of zeolitic imidazolate framework (ZIF) attached on graphene oxide to effectively prevent plasticization of polyimide membrane under mixed gas condition. ZIF nanofillers, known as suitable additive for olefin/paraffin separation membranes, were grown on graphene oxide 2-D nanotemplates to maximize encounter frequency between gas permeant and nanofillers even in lower concentrations. The prepared MMMs successfully showed an improved mixed gas selectivity compapred to pristine membrane, indicating better anti-plasticization effect.

Porous materials such as polymeric foam are widely adopted in engineering and biomedical fields. Porous materials often exhibit complex nonlinear behaviors and are sensitive to material and environmental factors including cell size and shape, amount of porosity, and temperature, which are influenced by the type of base materials, reinforcements, method of fabrication, etc. Hence, the material characteristics of porous materials such as compressive stress-strain behavior and void volume fraction according to aforementioned factors should be precisely identified. In this study, unconfined uniaxial compressive test for two types of closed-cell structure polyurethane foam, namely, 0.16 and 0.32 g/cm3 of densities were carried out. In addition, the void volume fraction of three different domains, namely, center, surface and buckling regions under various compressive strains (10%, 30 %, 50 % and 70 %) were quantitatively observed using Micro 3D Computed Tomography(micro-CT) scanning system. Based on the experimental results, the relationship between compressive strain and void volume fraction with respect to cell size, density and boundary condition were investigated.

The gas separation through membrane is considered as a promising solution for the stabilization of greenhouse gas level of atmosphere attributed from CO2. The separation process of membrane allows low energy requirement, low cost, and ease of operation. However, conventional polymeric membranes generally suffer from the trade-off between permeability and selectivity, which remains as one of the most important challenges for commercialization. Mixed matrix membranes (MMMs), consisting of a polymer matrix and porous nano-filler, are considered to be a promising solution to overcome the trade-offs in polymeric membranes. Herein the porous nano-structures were fabricated to enhance the permselectity of CO2 separation membranes. The MMM which were fabricated with prepared porous nano-filler showed permeability improvement without significant selectivity loss.

본 논문에서는 변형에 의해 유발된 패턴변화(pattern transformation)에 기반하여 압축(compression)과 인장(tension) 하중 모두에서 음의 포아송 비(negative poisson’s ratio)를 나타내는 다공성(porous) 구조를 제안한다. 기존에 개발된 원형 구멍을 이용한 구조는 연결선(ligament)의 회전 모멘트 부족으로 인해 인장 시 양의 포아송 비를 나타내는 한계점이 있었으며, 타원 형 구멍을 이용한 구조는 응력집중 현상으로 인하여 내구성(durability)이 약한 문제점이 있었다. 이에 본 연구에서는 휘어진 연결선의 배열을 통하여 인장하중 하에서의 회전 모멘트를 증가시키는 동시에 응력집중 현상을 완화하고 변형에너지(strain energy)를 구조물 전반에서 고르게 흡수하도록 설계하였다. 이를 통해 10%의 공칭 변형률(nominal strain) 범위 내의 압축 과 인장 모두에서 음의 포아송 비를 가지며, 기존 모델에 비하여 강성(stiffness)과 내구성이 개선된 구조를 개발하였다. 비선 형 유한요소해석을 통하여 기존 타원형 구멍 모델과의 비교를 수행하였으며 제안된 모델이 구조의 강성과 내구성 측면에서 현저히 개선됨을 확인하였다.

본 연구에서는 종결정 코팅층이 NaA 제올라이트 분리막 형성에 미치는 영향에 대하여 고찰하였다. NaA 제올라이트 분리막은 평균입경 100 nm 종결정을 다공성 α-알루미나 표면에 진공여과 코팅하고 100˚C에서 24시간 수열처리하여 합성되었다. 이때 지지체 표면에 분포된 종결정 양을 조절한 후 형성된 NaA 제올라이트 분리층의 두께와 결정입 크기 등 미세구조에 미치는 영향에 대하여 고찰하였다. 종결정 코팅 양은 지지체를 통과한 종결정 수용액의 여과 양을 조절하여 제어하였다. 종결정을 단일층으로 코팅한 후 합성하였을 경우, 코팅 양이 증가함에 따라 분리층 단면에서의 두께와 균일도는 증가하였으며, 표면에서의 결정입 크기는 감소하면서 균일도는 증가하였다. 반면, 종결정을 다층으로 코팅한 후 합성하였을 경우, 균일한 분리층을 형성하였지만 단일층으로 코팅된 경우에 비하여 불균일하였으며 두꺼운 분리층이 형성되었다. 균일하고 초박형의 결함이 없는 제올라이트 분리층을 형성하기 위해서는 종결정을 균일하고 단일층으로 코팅하여야 함을 알 수 있었다. 본 연구로부터 종결정의 코팅 상태가 이차성장에 의한 NaA 제올라이트 분리층의 미세구조를 결정하는 중요한 인자임을 확인할 수 있었다.

NiO catalysts were successfully coated onto FeCrAl metal alloy foam as a catalyst support via a dip-coating method. To demonstrate the optimum amount of NiO catalyst on the FeCrAl metal alloy foam, the molar concentration of the Ni precursor in a coating solution was controlled, with five different amounts of 0.4 M, 0.6 M, 0.8 M, 1.0 M, and 1.2 M for a dip-coating process. The structural, morphological, and chemical bonding properties of the NiO-catalyst-coated FeCrAl metal alloy foam samples were assessed by means of field-emission scanning electron microscopy(FESEM), scanning electron microscopy-energy dispersive spectroscopy(SEM-EDS), X-ray diffraction(XRD), and X-ray photoelectron spectroscopy(XPS). In particular, when the FeCrAl metal alloy foam samples were coated using a coating solution with a 0.8 M Ni precursor, well-dispersed NiO catalysts on the FeCrAl metal alloy foam compared to the other samples were confirmed. Also, the XPS results exhibited the chemical bonding states of the NiO phases and the FeCrAl metal alloy foam. The results showed that a dip-coating method is one of best ways to coat well-dispersed NiO catalysts onto FeCrAl metal alloy foam.

Ti-Ni alloys are widely used in numerous biomedical applications (e.g., orthodontics, cardiovascular science, orthopaedics) due to their distinctive thermomechanical and mechanical properties, such as the shape memory effect, superelasticity and low elastic modulus. In order to increase the biocompatibility of Ti-Ni alloys, many surface modification techniques, such as the sol-gel technique, plasma immersion ion implantation (PIII), laser surface melting, plasma spraying, and chemical vapor deposition, have been employed. In this study, a Ti-49.5Ni (at%) alloy was electrochemically etched in 1M H2SO4+ X (1.5, 2.0, 2.5) wt% HF electrolytes to modify the surface morphology. The morphology, element distribution, crystal structure, roughness and energy of the surface were investigated by scanning electron microscopy (SEM), energy-dispersive Xray spectrometry (EDS), X-ray diffractometry (XRD), atomic force microscopy (AFM) and contact angle analysis. Micro-sized pores were formed on the Ti-49.5Ni (at%) alloy surface by electrochemical etching with 1M H2SO4+ X (1.5, 2.0, 2.5) wt% HF. The volume fractions of the pores were increased by increasing the concentration of the HF electrolytes. Depending on the HF concentration, different pore sizes, heights, surface roughness levels, and surface energy levels were obtained. To investigate the osteoblast adhesion of the electrochemically etched Ti-49.5Ni (at%) alloy, a MTT test was performed. The degree of osteoblast adhesion was increased at a high concentration of HF-treated surface structures.

The synthesis behavior of nanoporous silica aerogel in the macroporous ceramic structure was observed using TEOS as a source material and glycerol as a dry control chemical additive (DCCA). Silica aerogel in the macroporous ceramic structure was synthesized via sono-gel process using hexamethyldiazane (HMDS) as a modification agent and n-hexane as a main solvent. The wet gel with a modified surface was dried at under ambient pressure. The addition of glycerol appears to give the wet gel a more homogeneous microstructure. However, glycerol also retarded the rate of surface modification and solvent exchange. Silica aerogel completely filled the macroporous ceramic structure without defect in the condition of surface modification (20% HMDS/nhexane at 36hr).

As a pore precursor, carbon black with different content of 0 to 60 vol% were added to (Ba,Sr) powder. Porous (Ba,Sr) ceramics were prepared by pressureless sintering at for 1h under air. Effects of carbon black content on the microstructure and PTCR characteristics of porous (Ba,Sr) ceramics were investigated. The porosity of porous (Ba,Sr) ceramics increased from 6.97% to 18.22% and the grain size slightly decreased from to with increasing carbon black contents. PTCR jump of the (Ba,Sr) ceramics prepared by adding carbon black was more than , and slightly increased with increasing carbon black. The PTCR jump in the (Ba,Sr) ceramics prepared by adding 40 vol% carbon black showed an excellent value of , which was above two times higher than that in (Ba,Sr) ceramics. These results correspond with Heywang model for the explanation of PTCR effect in (Ba,Sr) ceramics. It was considered that carbon black is an effective additive for preparing porous based ceramics. It is believed that newly prepared (Ba,Sr) cermics can be used for PTC thermistor.

A nano-porous structure of tin oxide was prepared using an anodic oxidation process and the sample's electrochemical properties were evaluated for application as an anode in a rechargeable lithium battery. Microscopic images of the as-anodized sample indicated that it has a nano-porous structure with an average pore size of several tens of nanometers and a pore wall size of about 10 nanometers; the structural/compositional analyses proved that it is amorphous stannous oxide (SnO). The powder form of the as-anodized specimen was satisfactorily lithiated and delithiated as the anode in a lithium battery. Furthermore, it showed high initial reversible capacity and superior rate performance when compared to previous fabrication attempts. Its excellent electrode performance is probably due to the effective alleviation of strain arising from a cycling-induced large volume change and the short diffusion length of lithium through the nano-structured sample. To further enhance the rate performance, the attempt was made to create porous tin oxide film on copper substrate by anodizing the electrodeposited tin. Nevertheless, the full anodization of tin film on a copper substrate led to the mechanical disintegration of the anodic tin oxide, due most likely to the vigorous gas evolution and the surface oxidation of copper substrate. The adhesion of anodic tin oxide to the substrate, together with the initial reversibility and cycling stability, needs to be further improved for its application to high-power electrode materials in lithium batteries.

To improve the filtration efficiency of porous materials used in filters, an extensive specific surface area is required to serve as a site for adsorption of impurities. In this paper, a method for creating a hybridized porous alloy using a powder metallurgical technique to build macropores in an Al-4 wt.% Cu alloy and subsequent surface modification for a microporous surface with a considerably increased specific surface area is suggested. The macropore structure was controlled by granulation, compacting pressure, and sintering; the micropore structure was obtained by a surface modification using a dilute NaOH solution. The specific surface area of surface-modified specimen increased about 10 times compare to as-sintered specimen that comprised of the macropore structure. Also, the surface-modified specimens showed a remarkable increase in micropores larger than 10 nm. Such a hybridized porous structure has potential for application in water and air purification filters, as well as membrane pre-treatment and catalysis.