• Composites Research
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• 제25권1호
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• pp.1-8
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• 2012

본 논문에서는 다공성 복합재료의 열탄성 거동 예측을 위하여 미시역학적 유한요소 해석을 통해 기공 탄성 인자를 측정하였다. 먼저 기공 압력에 의한 복합재료의 응력 및 변형 상태를 기술하기 위해서 구성 방정식에 기공 탄성 인자를 도입하였다. 기공 탄성 인자의 산출에 필요한 기공 압력에 의한 팽창 변형도와 기공 형성에 따른 균질화 탄성 계수의 저하를 측정하였다. 기공의 형상, 크기, 배열 형태에 따른 이차원 대표 체적 요소의 모델링과 유한요소 해석을 수행하였다. 기공도, 재료 이 방성이 기공 탄성 인자에 미치는 영향과 기공 압력에 따른 변형 에너지 밀도 분포를 살펴보았다. 또한, 측정된 기공 탄성 인자의 유용성을 검토하기 위하여 탄소/페놀릭 복합재료의 열탄성 거동을 예측하였다.

• 소성∙가공
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• 제27권2호
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• pp.93-99
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• 2018

An analytical solution for the tensile ductility in porous ductile materials was derived based on an Irwin's approach of the elastic-plastic deformation in fracture mechanics. This was in good agreement with the experimental results of a tensile ductility in a sintered pure Al, and could solve the discrepancies in the Brown and Embury, or the McClintock models. This model was also offered as an advanced analytical solution considering the effect of stress triaxiality of pore tip in addition to pore interactions, material properties of matrix, and local deformation effect around pore. The evaluation of an analytical solution in the sintered pure Al powder compacts showed that the tensile ductility depends not only on the volume fraction of pores, but also on the pore size and on the mechanical properties of the matrix. The tensile ductility of the sintered pure Al compacts decreased rapidly with the increasing of a pore volume fraction, despite of the excellent tensile ductility of the matrix. This significant decrease in the tensile ductility was mainly attributed to the low yield strength of the matrix and small pore size. Particularly, the effects of the large radius and high volume fraction of the pore on the tensile ductility in Al-Form, were thus reasonably predicted by this analytical equation.

• Bulletin of the Korean Chemical Society
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• 제34권2호
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• pp.569-573
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• 2013

In this study, activated carbon fabric was prepared from a cellulose-based polymer (viscose rayon) via a combination of physical and chemical activation (mixed activation) processes by means of $CO_2$ as a gasifying agent and surface and adsorption properties were evaluated. Experiments were performed to investigate the consequence of activation temperature (750, 800, 850 and $925^{\circ}C$), activation time (15, 30, 45 and 60 minutes) and $CO_2$ flow rate (100, 200, 300 and 400 mL/min) on the surface and adsorption properties of ACF. The nitrogen adsorption isotherm at 77 K was measured and used for the determination of surface area, total pore volume, micropore volume, mesopore volume and pore size distribution using BET, t-plot, DR, BJH and DFT methods, respectively. It was observed that BET surface area and TPV increase with rising activation temperature and time due to the formation of new pores and the alteration of micropores into mesopores. It was also found that activation temperature dominantly affects the surface properties of ACF. The adsorption of iodine and $CCl_4$ onto ACF was investigated and both were found to correlate with surface area.

• 환경위생공학
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• 제13권3호
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• pp.19-29
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• 1998

The calcination reactivity of limestone and physical property changes of calcined lime were investigated with a temperature($720~1000^{\circ}C$ under atmospheric gas($N_2$, $CO_2$) conditions. The mechanisms of mass transport in a lime matrix were represented by the evaporation and condensation (${\gamma}=1.7$) at $1000^{\circ}C$ and the volume diffusion (${\gamma}=2.7$) at $800^{\circ}C$, which was obtained by the specific surface area of calcined lime with sintering conditions. Also, the effect of physical property on the reactivity of sulfation reaction was determined by the changes of pore size with $lime-SO_2$ reaction in this work. The initial sulfation rate of calcined lime increased with increasing temperature, whereas the capture capacity of $SO_2$ exhibited a maximum value at $900^{\circ}C$. The pore volume of sulfated lime was decreased with increasing sulfation time, but the major pores shifted to the distribution of larger size at a temperature of $850{\;}~{\;}1000^{\circ}C$. The mean pore size of sulfated lime based on pore volume decreased gradually at $1000^{\circ}C$; however, it increased with sulfation time up to 40 min and rapidly decreased thereafter.

• 한국연초학회지
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• 제10권1호
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• pp.75-82
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• 1988

Cigarettes were made using a triple filter with several porous materials in its cavity. The removal effect of the adsorbents on carbon monoxide and hydrogen cyanide in cigarette smoke was investigated with the variation of their surface area and pore volume distributions. Several attempts were made to activated coconut shell based char under the fixed steam purging rate. 1. The specific surface area increased in number of micropore. It was found for transitional pore to have a little effect on the total surface area. 2. A Small amount of the particulate matter adsorbed on the adsorbents with transitional pores, Zeolite showed a little effect on the carbon monoxide adsorption though its small pore volume, but there was no significant difference in the adsorption capacity zeolite and the others. 3. In the adsorption for hydrogen cyanide as a vapor phase in cigarette smoke, the adsorption effect of the adsorbents increased remarkably with increasing their surface area and number of micropore. It was considered that the adsorbents with small pore volume like molecular seive 4A, in which the capillary diffusion of adsorbates could not be able, would not be effective for the adsorption of hydrogen cyanide.

• 콘크리트학회논문집
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• 제17권5호
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• pp.857-868
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• 2005

This paper deals with the accumulated damage in concrete structures due to the cyclic freeze-thaw as an environmental load. The cyclic ice body nucleation and growth processes in porous systems are affected by the thermo-physical and mass transport properties, and gradients of temperature and chemical potentials. Furthermore, the diffusivity of deicing chemicals shows significantly higher value under cyclic freeze-thaw conditions. Consequently, the disintegration of concrete structures is aggravated at marine environments, higher altitudes, and northern areas. However, the properties of cyclic freeze-thaw with crack growth and diffusion of chloride ion effects are hard to be identified in tests, and there has been no analytic model for the combined degradations. The main objective is to determine the driving force and evaluate the reduced strength and stiffness by freeze-thaw. For the development of computational model of those coupled deterioration, micro-pore structure characterization, pore pressure based on the thermodynamic equilibrium, time and temperature dependent super-cooling with or without deicing salts, nonlinear-fracture constitutive relation for the evaluation of internal damage, and the effect of entrained air pores (EA) has been modeled numerically. As a result, the amount of ice volume with temperature dependent surface tensions, freezing pressure and resulting deformations, and cycle and temperature dependent pore volume has been calculated and compared with available test results. The developed computational program can be combined with DuCOM, which can calculate the early aged strength, heat of hydration, micro-pore volume, shrinkage, transportation of free water in concrete. Therefore, the developed model can be applied to evaluate those various practical degradation cases as well.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2014년도 춘계 학술논문 발표대회
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• pp.146-147
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• 2014

In this study, as the resistance of the carbonation for high volume admixture incorporating concrete, coating effect of using refined cooking oil in the surface of high volume admixture incorporating concrete has been tested. The following results could be made as the conclusion. For the fresh concrete, the slump and air content has been identified as satisfying the target range. For the hardened concrete, comparing with specimen of Plain, specimen with coating showed better long age compressive strength. For the carbonation speed, the specimen of FA30 showed highest speed and the specimen of BS60 showed higher speed than specimen of Plain. For all the specimens coated with RCO, as the decrease of capillary pores inside the concrete, the carbonation speed has been obviously decreased and with even better effect than using PEP coating. It could be identified that specimens with coating by RCO showed good effect on refrain the speed of carbonation.

• Preventive Nutrition and Food Science
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• 제11권4호
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• pp.323-327
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• 2006

In this study, we examined the changes in loaf weight, loaf volume and specific volume, moisture content and water absorption, pH and titrable acidity, shape, texture profile and sensory evaluation using sour dough instead of dough conditioner in bread making. The weight and volume of bread tended to increase in the sour dough bread, compared to the control. The pH of bread tended to be lower in the sour dough bread. The control bread had large irregular pores that were fewer in number, while the sour dough bread had small spots and was very dense and even throughout the whole surface. The texture profile of bread such as hardness, cohesiveness, chewiness and brittleness was lower in the sour dough bread. There were no significant differences in the sensory characteristics of the breads, except for the shape of bread. However, the sour dough A bread was better in color, texture, flavor, touch, moistness, taste and overall acceptability, and the sour dough B bread was better in flavor, touch and taste than the control.

• 한국건축시공학회지
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• 제16권1호
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• pp.35-43
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• 2016

콘크리트는 대표적인 불균질 재료이며 콘크리트의 역학적 특성은 다양한 요인들에 의해 영향을 받는다. 그 중 콘크리트 내부에 존재하는 공극은 콘크리트의 강도를 결정하는데 많은 영향을 주고 있기 때문에 공극의 분포 및 크기를 파악하는 연구는 매우 중요하며 그 방법으로 화상이미지를 이용한 연구가 대두되고 있다. 경량 기포 콘크리트는 현재 비구조용에 관한 연구만 진행되고 있기 때문에, 구조용으로 사용하기 위한 경량 기포 콘크리트의 역학적 특성을 평가하고 화상 이미지를 기반으로 FEM 해석을 이용한 검증에 관한 연구는 미비하다. 그러므로 기포제 혼입률에 따른 시멘트 페이스트를 제작하여 역학적 성능 평가를 실시하고 화상 이미지를 이용하여 FEM 해석을 실시하여 역학적 성능 비교 및 검증을 실시하였다. 본 연구에서 기포제 혼입률에 따른 공극 분포를 확인하기 위해 7수준으로 하였으며 추 후 구조용 경량 기포 콘크리트에 대한 연구를 진행하기 위해 물-결합재비를 20%로 하였다. 기포제 혼입률이 0.8%에서 단위 용적 질량이 최소가 되었으며 그 이상 혼입했을 시 기포 간의 상호 연결로 인한 깨짐 현상이 발생하여 단위 용적 질량이 증가하였다. 공극 분포에 따른 FEM 해석을 위해 화상분석기(HF-MA C01)를 이용하여 시멘트 페이스트 단면을 촬영하였고 이를 토대로 OOF(Object Oriented Finite elements)를 이용한 FEM 해석을 실시한 결과 실험 탄성계수와 해석 탄성계수가 일치하였다.

• 한국입자에어로졸학회지
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• 제12권3호
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• pp.65-72
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• 2016

Nanoporous $SiO_2$ particles containing different pore volume and size were prepared from silicic acid by a spray pyrolysis. The pore size, pore volume and particle size could be controlled with varying the precursor concentration, reaction temperature, and amount of organic templates such as Urea and poly ethylene glycol (PEG). The pore size distribution, pore volume and specific surface area of as-prepared particles were analyzed by BET and BJH methods, and the average particle sizes were measured by a laser diffraction method. The nanoporous $SiO_2$ particles ranged $0.6-0.9{\mu}m$ in diameter were successfully synthesized and the average particle size increased as the silicic acid concentration increased. The morphology of nanoporous $SiO_2$ particles was spherical and pores ranged 1 - 40 nm in diameter were measured in the particles. In case of Urea added into silicic acid, it showed no much difference in the morphology, pore size and pore volume at different Urea concentration. On the other hand, when PEG was added, it was clearly observed that pore diameter and pore volume of the particles surface increased with respect to PEG concentration.