• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.12
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• pp.294-302
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• 2018

To analyze the behavior of a soil beam under pore water pressure, the results of analytical solutions and finite element analysis (FEM) were compared quantitatively. In contrast to the results of the analytical solution, the horizontal stress obtained from the FEM did not show a symmetrical distribution. On the other hand, the horizontal stress became closer to symmetrical distribution as the number of elements of the soil beam were increased. A comparison of the horizontal stresses from the analytic solution with those obtained from Gaussian points of FEM showed that the magnitude of the tensile stress from the FEM using 3 elements was 6% of the maximum value of the analytical solution and the compressive stress from the FEM using the same elements was 37% of the maximum value of the analytical solution. The magnitude of the tensile stress from the FEM using 6 elements was 61% of the maximum value of the analytical solution and the magnitude of the compressive stress from the FEM using the elements was 83% of the maximum value of the analytical solution. Vertical stresses, which were obtained from the analytical solution, showed a continuous distribution with the depth of the soil beam, whereas the vertical stresses from the FEM showed a discrete distribution corresponding to each element. The results also showed that the average value of the vertical stresses of each element was close to that of the pore water pressure. A comparison of the vertical displacements computed at the near vertical center line of the soil beam from the FEM with those of the analytical solution showed that the magnitude of the vertical displacement from FEM using 3 elements was 35% of the value of the analytical solution and the magnitude of the vertical displacement from FEM using 6 elements was 57% of the value of the analytical solution.

• Membrane Journal
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• v.19 no.1
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• pp.25-33
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• 2009

PES (polyethersulfone) membranes with highly enhanced their asymmetry were prepared by phase inversion process. The membranes were prepared by using PES/DMF (N,N-dimethylformamide)/TSA (p-toluenesulfonic acid)/PVP (polyvinylpyrrolidone) casting solution and water coagulant. The pre-coagulation of membrane surface which was induced by an addition of TSA as a demixing agent and PVP as a swelling polymer in the PES solution and humid exposure time, played a crucial role in determining morphological properties and the PWP (pure water permeation) performance. The PES solution was coated on polyester film under condition of 80% humidity for a while ($72{\sim}144$ sec) before immersing in a coagulation bath. The characterization of membranes was carried out by a capillary flow porometer, a FE-SEM and a permeation test apparatus. As the thickness of the smallest pore size layer (SPL) decreased, the asymmetry of membrane increased under conditions of 20 wt% of TSA and 10 wt% of PVP in 11 wt% of PES solution during longer humid contact time. As a result, the membranes showed a remarkable increase of PWP.

• Membrane Journal
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• v.25 no.1
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• pp.32-41
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• 2015

High performance polysulfone microfiltration membranes with a high were successfully prepared by vapor induced phase separation (VIPS) coupled with non-solvent induced phase separation (NIPS) process. Asymmetric Membranes were prepared with PSF/DMF/PVP/PEG/DMSO/water mixed solutions and water/IPA coagulant. PSF, DMF, PVP, PEG, DMSO, water was used as a membrane polymer, a solvent, a hydrophilic polymer additive, a polar protic liquid polymer, a polar aprotic nonsolvent, and a polar protic nonsolvent in the casting solution, respectively. The addition of polar aprotic nonsolvents, and polar protic nonsolvents is a convenient and effective method to control membrane structure. In order to control the morphology of polymeric membranes, the spontaneous emulsification induced by drawing water vapor into the exposed casting solution surface has been used. Control of the internal morphology of polymeric membranes by using mixed coagulation solution such as water and IPA is discussed in the present work. The pure water permeability, pore size distribution, surface hydrophilicity and membrane morphology were investigated. Due to the addition of DMSO to casting solution, the mean pore size increased almost $0.2{\mu}m$ and the water flux increased about 1000-1800 LMH.

• Membrane Journal
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• v.22 no.3
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• pp.178-190
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• 2012

Flat sheet membranes were prepared with polysulfone (PSF) by an immersion precipitation phase inversion method. Membranes were prepared with PSF/N-methylpyrrolidone (NMP)/polyvinylpyrrolidone (PVP)/phosphoric acid casting solution and water coagulant. By using the successive process of the vapor-induced phase inversion (VIPS) followed by the nonsolvent-induced phase inversion (NIPS), the effect of phosphoric acid addition to casting solution on morphology and permeability of membrane was studied. The mean pore size, the porosity, and the water flux of membranes were increased by the addition of small amount of phosphoric acid. Furthermore, the morphology of the prepared membranes were changed from a dense sponge-like structure to highly enhanced asymmetric structure. PSF/NMP/PVP/phosphoric acid/2-butoxyethanol (BE) casting solution were prepared and cast the successive VIPS-NIPS process with same experimental condition. Due to the addition of BE to casting solution, the mean pore size and almost 0.1 ${\mu}m$ and the water flux increased about 10 to 12 $L/cm^2{\cdot}min{\cdot}bar$.

• Membrane Journal
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• v.31 no.1
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• pp.67-79
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• 2021

Mesoporous polystyrene (PS) and polyethersulfone (PES) membranes have been fabricated by reverse-thermally induced phase separation (RTIPS) process, using flash freezing. The mesoporous pores can be created by the nano-scaled phase separation induced by the formation and growth of solvent crystals in the dope solution in RTIPS process. RTIPS process has been characterized through analysis on the enthalpy change in the solvent of the dope solution, the morphology of the membrane fabricated with different polymer content, and the pore size distribution and its standard deviation of pore size of the membrane with polymer content via DSC, SEM, and BET, respectively. It is found that the kinetic aspect of the dope solution, i.e., the crystallization of solvent is a crucial factor to determine the structure of membrane fabricated in RTIPS rather than the thermodynamic aspect of the dope solution.

• Corrosion Science and Technology
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• v.8 no.2
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• pp.74-80
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• 2009

The high alkaline property in the concrete pore solution protects the embedded steel in concrete from corrosion due to aggressive ions attack. However, a continuous supply of those ions, in particular, chlorides altogether with a pH fall in electrochemical reaction on the steel surface eventually depassivate the steel to corrode. To mitigate chloride-induced corrosion in concrete structures, finely grained mineral admixtures, for example, pulverized fuel ash (PFA), ground granulated blast furnace slag (GGBS) and silica fume (SF) have been often advised to replace ordinary Portland cement (OPC) partially as binder. A consistent assessment of those partial replacements has been rarely performed with respect to the resistance of each binder to corrosion, although the studies for each binder were extensively looked into in a way of measuring the corrosion rate, influence of microstructure or chemistry of chlorides ions with cement hydrations. The paper studies the behavior of steel corrosion, chloride transport, pore structure and buffering capacity of those cementitious binders. The corrosion rate of steel in mortars of OPC, 30% PFA, 60% GGBS and 10% SF respectively, with chloride in cast ranging from 0.0 to 3.0% by weight of binder was measured at 7, 28 and 150 days to determine the chloride threshold level and the rate of corrosion propagation, using the anodic polarization technique. Mercury intrusion porosimetry was also applied to cement pastes of each binder at 7 and 28 days to ensure the development of pore structure. Finally, the release rate of bound chlorides (i.e. buffering capacity) was measured at 150 days. The chloride threshold level was determined assuming that the corrosion rate is beyond 1-2 mA/$m^3$ at corrosion and the order of the level was OPC > 10% SF > 60% GGBS > 30% PFA. Mercury intrusion porosimetry showed that 10% SF paste produced the most dense pore structure, followed by 60% GGBS, 30% PFA and OPC pastes, respectively. It was found that OPC itself is beneficial in resisting to corrosion initiation, but use of pozzolanic materials as binders shows more resistance to chloride transport into concrete, thus delay the onset of corrosion.

• Journal of Pharmaceutical Investigation
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• v.40 no.4
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• pp.245-250
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• 2010

Porous poly(lactic-co-glycolic acid) microspheres (PLGA MS) have been utilized as an inhalation delivery system and a matrix scaffold system for tissue engineering. Here, gelatin (type A) is introduced as an extractable pH-responsive porogen, which is capable of controlling the porosity and pore size of PLGA microspheres. Porous PLGA microspheres were prepared by a water-in-oil-in-water ($w_1/o/w_2$) double emulsification/solvent evaporation method. The surface morphology of these microspheres was examined by varying pH (2.0~11.0) of water phases, using scanning electron microscopy (SEM). Also, their porosity and pore size were monitored by altering acidification time (1~5 h) using a phosphoric acid solution. Results showed that the pore-forming capability of gelatin was optimized at pH 5.0, and that the surface pore-formation was not significantly observed at pHs of < 4.0 or > 8.0. This was attributable to the balance between gel-formation by electrostatic repulsion and dissolution of gelatin. The appropriate time-selection between PLGA hardening and gelatin-washing out was considered as a second significant factor to control the porosity. Delaying the acidification time to ~5 h after emulsification was clearly effective to make pores in the microspheres. This finding suggests that the porosity and pore size of porous microspheres using gelatin can be significantly controlled depending on water phase pH and gelatin-removal time. The results obtained in this study would provide valuable pharmaceutical information to prepare porous PLGA MS, which is required to control the porosity.

• Proceedings of the KOSOMBE Conference
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• v.1997 no.11
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• pp.478-481
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• 1997

A technique or the preparation of porous polyurethane vascular prostheses was investigated. Small-diameter vessels are not in general clinical use due to their limited long-term biocompatibility and low patency rates in experimental trial. These limits are mainly due to the failure of mechanical unction of the vascular grafts. This failure has been suggested to result partially from compliance mismatch. The long-term patency is considered to depend critically on the properties of the material and the fabrication process of the graft. So the control of pores is very important and main points to develop a available vascular grafts. Two-kind polymer sheets was compared. One was the porous PU-sheet made at room temperature by the solvent/non-solvent exchange. And the other was the porous PU-sheet which was fabricated by thermal phase transition and solvent-/non-solvent exchange using the thermal controller. The polymer sheets had a uniform pore size and pore occupation. According to the result of the above experiments, polyurethane solution was injected into a mold designed or U-type tube. The average pore size and pore occupation were easily changed by changing polyurethane concentration, freezing temperature, and methods. This technique can give a proper pore size ($10{\sim}45\;{\mu}m$) or tissue in growth, and suitable compliances or matching with arteries and veins. Besides, the fabrication of more complicated shaped vessels such as the U-type vascular grafts is easily controlled by using the fixed mold. this method might give a desired compliant graft or artificial implantation with the presently valid medical polymers.

• Korean Journal of Environmental Agriculture
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• v.28 no.4
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• pp.386-391
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• 2009

The purpose of this study is to elucidate the adsorption properties of fly ash (FA)-derived zeolites A and X for the divalent cationic herbicides, paraquat and diquat. Their adsorption isotherms were well fitted to the Langmuir equation, indicating that adsorption mainly occurred on the crystal surface. FA-zeolite X showed a higher adsorption capacity than that of FA-zeolite A due to wide pore window size in spite of its low CEC. The equilibrium adsorption increased with increasing the reaction temperature because of the enhanced molecule activity and the thermal expansion of zeolite pore windows. Overall, these results demonstrated that the FA-zeolite synthesized from fly ash could be used as a low-cost mineral adsorbent for the removal of environmental cationic organic pollutants from the aqueous solution.

• Geomechanics and Engineering
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• v.8 no.3
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• pp.323-359
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• 2015

This paper presents an elasto-plastic model for determination of the ground response curve of a circular underwater tunnel excavated in elastic-strain softening rock mass compatible with a nonlinear Hoek-Brown yield criterion. The finite difference method (FDM) was used to propose a new solution to calculate pore water pressure, stress, and strain distributions on periphery of circular tunnels in axisymmetric and plain strain conditions. In the proposed solution, a modified non-radial flow pattern, for the hydraulic analysis, is utilized. To evaluate the effect of gravitational loads and variations of pore water pressure, the equations concerning different directions around the tunnel (crown, wall, and floor) are derived. Regarding the strain-softening behavior of the rock mass, the stepwise method is executed for the plastic zone in which parameters of strength, dilatancy, stresses, strains, and deformation are different from their elasto-plastic boundary values as compared to the tunnel boundary values. Besides, the analytical equations are developed for the elastic zone. The accuracy and application of the proposed method is demonstrated by a number of examples. The results present the effects of seepage body forces, gravitational loads and dilatancy angle on ground response curve appropriately.