• 한국세라믹학회지
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• 제56권2호
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• pp.178-183
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• 2019

A process of fabricating the foamed glass that has closed pores with 8 ~ 580 ㎛ sizes without a blowing agent by sintering 10 ㎛ boron-free glass powder composed of CaO, MgO, SO₃, Al₂O₃-83 wt% SiO₂ at a molding pressure of 0 ~ 120 MPa and a sintering temperature of 750 ~ 1000℃ was investigated. To analyze the glass transition temperature of glass powder, thermogravimetric analysis-differential thermal analysis (TGA-DTA) method were used. The microstructure and pore size of foamed glass were examined using the optical microscopy and field emission scanning electron microscopy (FE-SEM). For the thermal diffusivity and color of the fabricated samples, a heat flow meter and ultraviolet-visible-near-infrared (UV-VIS-NIR)-colormetry were used, respectively. In the TGA-DTA result, the glass transition temperature of glass powder was confirmed to be 626℃. In the microstructure result, closed pores of 7 ~ 20 ㎛ were formed at 750 ~ 900℃, and they were not affected by the molding pressure and sintering temperature. However, at 1,000℃, when there was 0 MPa molding pressure, closed pores of 580 ㎛ were confirmed, and the pore size decreased as the molding pressure increased. Moreover, at a molding pressure of 30 MPa or higher, closed pores of approximately 400 ㎛ were formed. The porosity showed an increasing trend of smaller molding pressure and larger sintering temperature, and it was controllable in the range of 5.69 ~ 68.45%. In the thermal diffusivity result, there was no change according to the molding pressure, and, by increasing the sintering temperature, up to 0.115 W/m·K could be obtained. The Lab color index (CIE-Lab) results all showed a similar translucent white color regardless of molding pressure and sintering temperature. Therefore, based on the foamed glass without boron and blowing agent, it was confirmed that white foamed glass, which has closed pores of 8 ~ 580 ㎛ and a thermal diffusivity characteristic of 0.115 W/m·K, can be fabricated by changing the molding pressure and sintering temperature.

• 한국결정성장학회지
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• 제18권6호
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• pp.258-263
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• 2008

입자를 부유 상태에서 소성할 수 있는 수직로를 이용하여 2 mm 이하 크기의 경량 세골재를 제조하고 그 물리적 특성을 고찰하였다. $1200{\sim}1300^{\circ}C$에서 소성된 대부분 시편은 표면에 다량의 액상이 발달하였고 따라서 내부의 가스가 팽창하여 다공성의 중앙부와 상대적으로 치밀한 표피층이 형성되었다. 특히 압출 성형체를 파쇄시켜 얻은 부정형의 C 계열 시편은 $1300^{\circ}C$ 이상으로 소결하면 내부에 가스가 팽창하여 시편 전체가 부풀어져서 구형으로 되었다. 본 부유 수직로에서 소성된 시편의 겉보기 비중은 $0.68{\sim}1.08$ 범위로 대부분 물에 뜰 정도의 경량이었다. 제조된 경량 세골재의 흡수율은 기공율과 비례하였고, 따라서 내부 기공들이 완전 고립된 폐쇄기공은 아님을 나타내었다. 부유소성로에서 제조된 세골재는 전기 머플로에서 소성된 시편과 비슷한 물성을 나타내었으나, 전기로에서 나타나는 골재 간 융착 현상이 발생하지 않았다. 수직로에서 부유소성된 세골재의 내충격성은 자연골재보다 다소 낮았으나, 단위용적중량은 KS 규격 기준을 만족하였다.

• Wind and Structures
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• 제22권4호
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• pp.429-454
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• 2016

In this paper, a shear deformation plate theory based on neutral surface position is developed for free vibration analysis of functionally graded material (FGM) plates. The material properties of the FGM plates are assumed to vary through the thickness of the plate by a simple power-law distribution in terms of the volume fractions of the constituents. During manufacture, defects such as porosities can appear. It is therefore necessary to consider the vibration behavior of FG plates having porosities in this investigation. The proposed theory is based on assumption that the in-plane and transverse displacements consist of bending and shear components, in which the bending components do not contribute toward shear forces and, likewise, the shear components do not contribute toward bending moments. The neutral surface position for a functionally graded plate which its material properties vary in the thickness direction is determined. The equation of motion for FG rectangular plates is obtained through Hamilton's principle. The closed form solutions are obtained by using Navier technique, and then fundamental frequencies are found by solving the results of eigenvalue problems. Numerical results are presented and the influences of the volume fraction index and porosity volume fraction on frequencies of FGM plates are clearly discussed.

• 한국의류학회지
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• 제20권1호
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• pp.228-238
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• 1996

The purpose of this study was to evaluate the effect of chacteristics of knit fabrics on the microclimate of the skin simulating system. To determine the effect of characteristics of knit fabrics, vapor state of sweat pulse was simulated in the closed system. Different contents of fibers such as cotton, wool and polyester with different yarn size and knit types were chosen for specimens. The changes of humidity and temperature of air layer in the simulated systems were measured. Buffering indices, $K_d$ and $\beta_r$, were determined by considering $\alpha_p, \DeltaP_{max}, t_{max}, and tan\beta$. Physical properties of knit fabrics such as thickness, porosity, air resistance and moisture vapor transport were measured. Results showed that vapor pressure of wool was lower than cotton or polyester This was attributed to the hydrophilicity of wool which absorbed moisture rather quickly and retained in the knit fabric. The time to decrease vapor pressure was faster for polyester than cotton or wool. As a result, $K_d$ was in the order of wool> polye, item> cotton. $\beta_r$ of wool was rower than cotton or polyester due to its lowers porosity and slower desorption rate. For the yarn size, $K_d$ was in the order of 80's> 60's> 30's; thinner and lighter yarn showed better water vapor transport property. For knit type, buffering capacity of single jersey was better than interlock knit fabric. Statistical analysis showed that the air permeability was the most influential factor far the water vapor transport properties.

• Steel and Composite Structures
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• 제43권5호
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• pp.581-601
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• 2022

The main objective of this research work is to investigate the free vibration behavior of annular sandwich plates resting on the Kerr foundation at thermal conditions. This sandwich configuration is composed of two FGM face sheets as coating layer and a porous GPLRC (GPL reinforced composite) core. It is supposed that the GPL nanofillers and the porosity coefficient vary continuously along the core thickness direction. To model closed-cell FG porous material reinforced with GPLs, Halpin-Tsai micromechanical modeling in conjunction with Gaussian-Random field scheme is used, while the Poisson's ratio and density are computed by the rule of mixtures. Besides, the material properties of two FGM face sheets change continuously through the thickness according to the power-law distribution. To capture fundamental frequencies of the annular sandwich plate resting on the Kerr foundation in a thermal environment, the analysis procedure is with the aid of Reddy's shear-deformation plate theory based high-order shear deformation plate theory (HSDT) to derive and solve the equations of motion and boundary conditions. The governing equations together with related boundary conditions are discretized using the generalized differential quadrature (GDQ) method in the spatial domain. Numerical results are compared with those published in the literature to examine the accuracy and validity of the present approach. A parametric solution for temperature variation across the thickness of the sandwich plate is employed taking into account the thermal conductivity, the inhomogeneity parameter, and the sandwich schemes. The numerical results indicate the influence of volume fraction index, GPLs volume fraction, porosity coefficient, three independent coefficients of Kerr elastic foundation, and temperature difference on the free vibration behavior of annular sandwich plate. This study provides essential information to engineers seeking innovative ways to promote composite structures in a practical way.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2009년도 춘계 학술발표회
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• pp.154-163
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• 2009

The groutability depends on the properties of the grout, its injection processes, and on the mechanical properties of the soil formation. During the process of pouring cement-based grouting into a porous medium, a variation with time occurs in the viscosity of grout suspension. In addition the particle filtration phenomenon will limit the expansion of the grouted zone because cement particles are progressively stagnant within the soil matrix. In this paper, a closed-form solution was derived by implementing the mass balance equations and the generalized phenomenological filtration law, which can be used to evaluate the deposition of cement-based grout in the soil matrix. The closed-form solution relevant to a particular spherical flow was modified by a step-wise numerical calculation, considering the variable viscosity caused by a chemical reaction, and the decrease in porosity resulting from grout particle deposition in the soil pores. A series of pilot-scale chamber injection tests was performed to verify that the developed step-wise numerical calculation is able to evaluate the injectable volume of grout and the deposition of grout particles. The results of the chamber injection tests concurred well with that of the step-wise numerical calculation. Based on the filtration phenomenon, a new groutability criterion of cement-based grout in a porous medium was proposed, which might facilitate a new insight in the design of the grouting process.

• 한국지하수토양환경학회지:지하수토양환경
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• 제23권2호
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• pp.1-14
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• 2018

The recent increase in demand for lithium has led to the development of new brine prospects, The brines are hosted in closed salar basin aquifers of two types that are mature halite salars and immature clastic salars. Salar brines also contain other elements of commercial interest, most notably potassium and boron. As a result, there has been a plethora of new exploration projects focused on the brines hosted in the aquifers of the intermontane-closed basins. The estimate of lithium resources and reserves in these salars depends on a detailed knowledge of aquifer geometry, porosity, and brine grade. Because the resource is in a fluid state, it has the propensity to move, mix, rearrange itself relatively rapidly during the course of a project lifetime, and lower recovery factors compared with most metalliferous and industrial mineral deposits due to reliance on pumping of the brine from wells for extraction. This is unlike any other type of metallic mineral resource and hence a different approach specially focusing on hydrogeology and brine hydrology is required for these prospects.

• 한국석유지질학회지
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• 제3권1호
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• pp.16-27
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• 1995

전기마이오세의 템블러층은 캘리포니아의 케틀만노스돔 유전에서 중요한 사암의 저류층을 이루고 있다. 이 층의 사암은 대부분이 아코스의 성분을 가지나 최하부에는 많은 화산암의 암편이 함유되어 있다. 템블러층 사암에서 장석이 변질작용을 받기 이전에 일어난 속성작용의 단계를 순서대로 열거하면 초기의 방해석, 백운석, 석영, 알바이트, 녹니석과 스멕타이트의 혼합층 점토광물, 스멕타이트와 무수석고의 교질작용이 일어났다. 장석과 관련되어 일어난 속성작용으로는 사장석의 알바이트화작용, 후기의 방해석과 러몬타이트의 교질작용과 교대작용, 사장석의 용해, 카올리나이트의 교질작용이 있다. 사장석의 알바이트화작용과 후기의 방해석과 러몬타이트의 교질작용은 템블러층사암이 온도 약 130도 정도로 가장 깊이 매몰되었을 때 일어났다. 사장석 중 화산기원의 사장석이 선택적으로 알바이트화작용을 받았다. 이 사암층에 일어난 대부분의 속성작용은 약 1백만년 전에 일어난 이 층의 융기 이전에 일어났다. 융기를 할 때부터 석유가 배태되기 이전에 사장석의 용해와 카올리나이트의 교질작용이 일어났다. 이 때의 속성작용은 카올리나이트가 사장석이 용해되는 장소 바로 옆에 일어난 점으로 미루어 볼 때 아마도 지구화학적으로 폐쇄된 환경에서 일어났음을 짐작할 수 있다. 이 층이 가장 깊이 매몰이 일어났을 당시 알바이트화작용을 겪지 않았던, 화산기원 사장석의 변질을 받지 않은 부분과 약간의 심성암 기원의 사장석이 선택적으로 용해되어 사장석의 용해공극을 형성하였다. 사장석의 용해작용과 탄산염과 무수석고 교질물의 용해작용이 일어나 이차공극이 형성되었는데, 이차공극은 유기물의 카타제네시스동안 발생한 유기산이 함유되 어 있는 산성의 공극수에 의하여 형성된 것으로 해석된다.

• Bulletin of the Korean Chemical Society
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• 제28권12호
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• pp.2481-2485
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• 2007

Spatially resolved, quantitative, non-destructive analysis using synchrotron x-ray reflectivity (XR) with subnano-scale resolution was successfully performed on the nanoporous organosilicate thin films for low dielectric applications. The structural information of porous thin films, which were prepared with polymethylsilsesquioxane and thermally labile 4-armed, star-shaped poly(ε-caprolactone) (PCL) composites, were characterized in terms of the laterally averaged electron density profile along with a film thickness as well as a total thickness. The thermal process used in this work caused to efficiently undergo sacrificial thermal degradation, generating closed nanopores in the film. The resultant nanoporous films became homogeneous, well-defined structure with a thin skin layer and low surface roughness. The average electron density of the calcined film reduced with increase of the initial porogen loading, and finally leaded to corresponding porosity ranged from 0 to 22.8% over the porogen loading range of 0-30 wt%. In addition to XR analysis, the surface and the inner structures of films are investigated and discussed with atomic force and scanning electron microscopy images.

• Steel and Composite Structures
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• 제9권6호
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• pp.569-584
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• 2009

Corrosion of steel rebars in bridge decks which are faced to harsh conditions, is a common problem in construction industries due to the porosity of concrete. In this research, the behavior of one-way concrete slabs reinforced with Glass fiber reinforced polymer (GFRP) molded grating is investigated both theoretically and experimentally. In the analytical method, a closed-form solution for load-deflection behavior of a slab under four-point bending condition is developed by considering a concrete slab as an orthotropic plate and defining stiffness coefficients in principal directions. The available formulation for concrete reinforced with steel is expanded for concrete reinforced with GFRP molded grating to predict ultimate failure load. In finite element modeling, an exact nonlinear behavior of concrete along with a 3-D failure criterion for cracking and crushing are considered in order to estimate the ultimate failure load and the initial cracking load. Eight concrete slabs reinforced with steel and GFRP grating in various thicknesses are also tested to verify the results. The obtained results from the models and experiments are relatively satisfactory.