• 한국결정성장학회지
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• 제31권4호
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• pp.182-189
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• 2021

무기질 단열재 개발을 위해 포말법을 이용하여 다공성 세라믹스를 제조하였다. 실리카 흄과 SiO₂를 주 원료로 사용하였으며, 다공성 세라믹의 균일한 기공 형성을 위한 첨가제로 벤토나이트를 사용하였다. 다공성 세라믹은 1200℃에서 소결하였으며, 기공율, 밀도, 압축강도, 미세구조 그리고 열전도도 분석을 수행하였다. 다공성 세라믹은 SiO₂에 대한 실리카흄의 함량이 70~90 % 증가할수록 비중이 0.63에서 0.69로 증가하였으며, 압축강도는 9.41 Mpa에서 12.86 Mpa로 증가하였다. 그러나, 기공율은 비중과 반대로 72.07 %에서 70.82 %로 감소하는 경향을 나타내었다. 열전도도 측정 결과, 실리카 흄의 함량이 70 %인 F7S3 다공성 세라믹의 경우 25~800℃ 온도조건에서 0.75~0.72 W/m·K의 열전도도를 나타내었으며, 실리카 흄의 함량이 90 %인 F9S1 다공성 세라믹의 경우 0.66~0.86 W/m·K를 나타내어 실리카 흄 함량이 적을수록 낮은 열전도도를 나타내었다. 이는 기공율 결과와 일치한 것을 확인하였다. SEM(Scanning Electron Microscope)을 이용한 미세구조 분석 결과, 다공성 세라믹 내/외부에 전체적으로 수십~수백 ㎛ 범위 기공이 관찰되었으며 기공 분포가 비교적 균일한 것을 확인할 수 있었다.

• 한국해양공학회지
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• 제19권4호
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• pp.9-14
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• 2005

In the present paper, the wave absorbing performance of the fully submerged horizontal porous plates has been investigated, numerically and experimentally. The submerged porous system is composed of multi-layered horizontal porous plates that are clamped at the vertical setwall, which are slightly inclined and placed vertically, in parallel, with spacing. The hydrodynamic interaction of incident waves with the rigid porous multi-layered plates was formulated within the context of linear wave-body interaction theory and Darcy's law. In order to validate the effectiveness of the present computing code, the numerical results were compared with the analytical and experimental results. It is found that triple horizontal porous plates with slight inclination, if properly tuned for wave energy dissipation against the standing waves in front of the vertical wall, can have high performances in reducing the reflected wave amplitudes against the incident waves over a wide range of wave frequency.

• 한국재료학회:학술대회논문집
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• 한국재료학회 2009년도 추계학술발표대회
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• pp.38.2-38.2
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• 2009

Regeration of natural tissuesor to create biological substitutes for defective or lost tissues and organs through the use of cells. In addition to cells and their porous, drugs are required to promote tissue regeneration. Therefore, the present studies were prepared using simvastatim loaded porous poly(lactide-co-glycolide) (PLGA) by double emulsion solvent evaporation water-in-oil-in-water technique (W/O/W) as drug delivery system strategies for injuring tissue. The resulting microspheres were evaluated for morphology, particle size, encapsulation efficiency, degradation of PLGA microspheres in vitro drug release and in vitro cell viability. Scanning electronic microscopic (SEM) showed that the porosities of the particles was changed by experimental conditions and cultured cells were attached well on porous microspheres surface. The X-ray diffraction (XRD) and differential scanning calometry (DSC) analysis indicate thatsimvastatim was highly dipersed in the microsphere at amorphousstate.

• 한국분말재료학회지
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• 제19권4호
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• pp.259-263
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• 2012

Dependence of the freeze-drying process condition on microstructure of porous W and pore formation mechanism were studied. Camphene slurries with $WO_3$ contents of 10 vol% were prepared by milling at $50^{\circ}C$ with a small amount of dispersant. Freezing of a slurry was done in Teflon cylinder attached to a copper bottom plate cooled at $-25^{\circ}C$. Pores were generated subsequently by sublimation of the camphene during drying in air for 48 h. The green body was hydrogen-reduced at $800^{\circ}C$ for 30 min, and sintered in the furnace at $900^{\circ}C$ for 1 h. After heat treatment in hydrogen atmosphere, $WO_3$ powders were completely converted to metallic W without any reaction phases. The sintered samples showed large pores with the size of about $70{\mu}m$ which were aligned parallel to the camphene growth direction. Also, the internal wall of large pores and near bottom part of specimen had relatively small pores with dendritic structure due to the growth of camphene dendrite depending on the degree of nucleation and powder rearrangement in the slurry.

• 한국세라믹학회지
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• 제41권7호
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• pp.513-517
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• 2004

기공크기와 형태를 제어하여 열전도도 이방성을 나타내기 위해 판상의 기공이 배향된 다공질 알루미나 소결체의 제조방법을 연구하였다. 속이 가스로 차있는 열가소성 고분자 microsphere를 알루미나 분말과 혼합한 후 일축 가압 열변형 방법을 이용하여 15 MPa의 압력으로 가압한 상태에서 20$0^{\circ}C$까지 승온하여 microsphere를 판상으로 변형시킨 후, 1,00$0^{\circ}C$에서 1시간동안 소결하였다. Microsphere의 함량이 10wt%인 경우 45.3%의 기공율을 나타내었으며, 44 MPa의 꺾임강도 값을 나타내었다. 미세구조를 살펴본 결과 판상기공이 압축방향과 수직방향으로 배향되었으며, 열전도도를 측정한 결과 압축방향으로 3.803 W/mK, 측면방향으로는 7.818 W/mK로서 두 값의 비는 2 이상이었다.

• 통합자연과학논문집
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• 제3권3호
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• pp.168-173
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• 2010

Novel porous silicon chip exhibiting dual optical properties, both Frbry-Perot fringe (optical reflectivity) and photoluminescence had been developed and used as chemical sensors. Porous silicon samples were prepared by an electrochemical etch of p-type sillicon wafer (boron-doped, <100> orientation, resistivity 1 - 10 ${\Omega}$). The ething solution was prepared by adding an equal volume of pure ethanol to an aqueous solution of HF (48% by weight). The porous silicon was illuminated with a 300 W tungsten lamp for the duration of etch. Ething was carried out as a two-electrode Kithley 2420 preocedure at an anodic current. The surface of porous silicon was characterized by FT-IR instrument. The porosity of samples was about 80%. Three different types of porous silicon, fresh porous silicon (Si-H termianated), oxidized porous silicon (Si-OH terminated), and surface-derivatized porous silicon (Si-R terminated), were prepared by the thermal oxidation and hydrosilylation. Then the samples were exposed to the wapor of various organics vapors. such as chloroform, hexane, methanol, benzene, isopropanol, and toluene. Both reflectivity and photoluminescence were simultaneously measured under the exposure of organic wapors.

• 통합자연과학논문집
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• 제3권3호
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• pp.153-156
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• 2010

Oxidation behaviors of porous silicon were investigated by the measurement of area of $SiO_2$ vibrational peaks in FT-IR spectra during thermal oxidation of porous silicon at corresponding temperatures. Visible photoluminescent porous silicon samples were obtained from an electrochemical etch of n-type silicon of resistivity between 1-10 ${\Omega}/cm$. The etching solution was prepared by adding an equal volume of pure ethanol to an aqueous solution of HF. The porous silicon was illuminated with a 300 W tungsten lamp for the duration of etch. Etching was carried out as a two-electrode galvanostatic procedure at applied current density of 200 $mA/cm^2$ for 5 min. The porosity of samples prepared was about 80%. After formation of porous silicon, the samples were thermally oxidized at $100^{\circ}C$, $200^{\circ}C$, $300^{\circ}C$, and $400^{\circ}C$, respectively. The growth rate of $SiO_2$ layer of porous silicon was investigated by using FT-IR spectroscopy. The effect of oxidation of porous silicon was presented.

• 한국분말재료학회지
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• 제29권2호
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• pp.118-122
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• 2022

The synthesis of porous W by freeze-casting and vacuum drying is investigated. Ball-milled WO₃ powders and tert-butyl alcohol were used as the starting materials. The tert-butyl alcohol slurry is frozen at -25℃ and dried under vacuum at -25 and -10℃. The dried bodies are hydrogen-reduced at 800℃ and sintered at 1000℃. The XRD analysis shows that WO₃ is completely reduced to W without any reaction phases. SEM observations reveal that the struts and pores aligned in the tert-butyl alcohol growth direction, and the change in the powder content and drying temperature affects the pore structure. Furthermore, the struts of the porous body fabricated under vacuum are thinner than those fabricated under atmospheric pressure. This behavior is explained by the growth mechanism of tert-butyl alcohol and rearrangement of the powders during solidification. These results suggest that the pore structure of a porous body can be controlled by the powder content, drying temperature, and pressure.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제50권9호
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• pp.444-449
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• 2001

In this paper, a novel ultraviolet sensor is presented based on a photoluminescent porous silicon. Porous silicon layer was formed by chemical etching of surface of pn junction in a $HF(48%)-HNO_3(60%)-H_20$ solution. Incident ultraviolet(UV) light is converted to visible light by photoluminescent porous silicon layer, and then this visible light generates electron-hole pairs in the pn junction, which produces a photocurrent flow through the device. In order to maximize detection efficiency, the peak sensitivity wavelength of the pn junction diode was matched with the peak wavelength of Photoluminescence from porous silicon layer. The porous silicon ultraviolet sensor showed a large output current as UV intensity increases and but very low sensitivity to visible light. The detection sensitivity of porous silicon sensor was calculated as 2.91mA/mW. These results are expected to open up a possibility that the present porous silicon sensor can be used for detecting UV light in a visible background, compared to silicon UV detectors which have an undesirable response to visible light.

• 한국분말재료학회지
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• 제18권2호
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• pp.149-158
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• 2011

Electro-Discharge Sintering (EDS) employs a high-voltage/high-current-density pulse of electrical energy, discharged from a capacitor bank, to instantaneously consolidate powders. In the present study, a single pulse of 0.57-1.1 kJ/0.45 g-atomized spherical $Ti_{52}Zr_{28}Ni_{20}$ powders in size range of 10~30 and $30\sim50{\mu}m$ consisting of ${\beta}$-(Ti, Zr) and icosahedral phases were applied to examine the structural evolution of icosahedral phase during EDS. Structural investigation reveals that high electrical input energy facilitates complete decomposition of icosahedral phase into C14 laves and ${\beta}$-(Ti, Zr) phases. Moreover, critical input energy inducing decomposition of the icosahedral phase during EDS depends on the size of the powder. Porous Ti and W compacts have been fabricated by EDS using rectangular and spherical powders upon various input energy at a constant capacitance of $450{\mu}F$ in order to verify influence of powder shape on microstructure of porous compacts. Besides, generated heat (${\Delta}H$) during EDS, which is measured by an oscilloscope, is closely correlated with powder size.