• E2M - 전기 전자와 첨단 소재
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• 제9권8호
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• pp.825-830
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• 1996

In this study, Characteristics of Ultrasonic Transducer fabricated with porous piezoelectric resonator, 3-D underwater object restoration using the self made ultrasonic transducer and modified SCL(Simple Competitive Learning) neural network are investigated. The self-made transducer was satisfied the required condition of ultrasonic transducer in water, and the modified SCL neural network using the acquired object data 16*16 low resolution image was used for object restoration of $32{\times}32$ high resolution image. The experimental results have shown that the ultrasonic transducer fabricated with porous piezoelectric resonator could be applied for SONAR system.

• 설비공학논문집
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• 제28권1호
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• pp.21-28
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• 2016

A typical heat exchanger, found in many industrial sites, is made up of a large number of unitary cells, which causes difficulties when carrying out full-scale three-dimensional numerical simulations of the heat exchanger to analyze the aero-thermal performance. In the present study, a three-dimensional numerical study using a porous media model was carried out to evaluate the performance of the heat exchanger modelled in two different ways : full-scale and simplified. The pressure drop in the air side and gas side along with the overall heat transfer rate were calculated using a porous media model and the results were then compared to results obtained with a one-dimensional flow network model. The comparison between the results for two different geometries obtained using a porous media model and a one-dimensional flow network model shows good agreement between the simplified geometry and the one-dimensional flow network model. The full-scale geometry shows reasonable differences caused by the geometry such as sudden expansion and contraction.

• Bulletin of the Korean Chemical Society
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• 제32권12호
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• pp.4392-4396
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• 2011

Porous silicon with a complex network of nanopores is utilized for photoelectrochemical energy conversion. A novel electroless Pt deposition onto porous silicon is investigated in the context of photoelectrochemical hydrogen generation. The electroless Pt deposition is shown to improve the characteristics of the PS photoelectrode toward photoelectrochemical $H^+$ reduction, though excessive Pt deposition leads to decrease of photocurrent. Furthermore, it is found that a thin layer (< 10 ${\mu}m$) of porous silicon can serve as anti-reflection layer for the underlying Si substrate, improving photocurrent by reducing photon reflection at the Si/liquid interface. However, as the thickness of the porous silicon increases, the surface recombination on the dramatically increased interface area of the porous silicon begins to dominate, diminishing the photocurrent.

• 한국세라믹학회지
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• 제45권10호
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• pp.584-588
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• 2008

Porous hydroxyapatite(HA) and HA-coated porous $Al_2O_3$ possessing pore characteristics required for bone substitutes were prepared by a slurry foaming method combined with gelcasting. The HA coating was deposited by heating porous $Al_2O_3$ substrates in an aqueous solution containing $Ca^{2+}$ and ${PO_4}^{3-}$ ions at $65{\sim}95^{\circ}C$ under ambient pressure. The pore characteristic, microstructure, and compressive strength were investigated and compared for the two kinds of samples. The porosity of the samples was about 81% and 80% for HA and $Al_2O_3$, respectively with a highly interconnected network of spherical pores with size ranging from 50 to $250{\mu}m$. The porous $Al_2O_3$ sample showed much higher compressive strength(25 MPa) than the porous HA sample(10 MPa). Fairly dense and uniform HA coating(about $2{\mu}m$ thick) was deposited on the porous $Al_2O_3$ sample. Since the compressive strength of cancellous bone is $2{\sim}12$ MPa, both the porous HA and HA-coated porous $Al_2O_3$ samples could be successfully utilized as scaffolds for bone repair. Especially the latter is expected suitable for load bearing bone substitutes due to its excellent strength.

• 한국세라믹학회지
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• 제43권4호
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• pp.199-202
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• 2006

In this study, SiC whiskers were grown on a porous SiC diesel particulate filter for nanoparticle filtering. To grow the whiskers at the inner pore without closing the pores, we used chemical vapor infiltration with a solution source and a dilute. As the deposition time increased, the whiskers grew and formed a network structure. After 180 min of deposition, the mean diameter of the whiskers was 174 nm and the compressive strength was 58.4 MPa. The pores shrank from $10{\mu}m\;to\;0.4{\mu}m$ and, because the whiskers filed the inner pores, the gradient of permeability decreased as the deposition time increased. However, by using the network structure of whiskers deposited for 120 min and 180 min, we obtained a diesel particulate filter with pores of $0.98{\mu}m\;and\;0.4{\mu}m$, respectively. Furthermore, the filter shows better permeability than a porous body with pores of $1{\mu}m$. In short, by filtering the nanoparticulate materials, the network structure of whiskers improves the strength, reduces the pore size and minimizes the permeability drop.

• E2M - 전기 전자와 첨단 소재
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• 제10권9호
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• pp.916-921
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• 1997

In this study Characteristics of 3-D underwater object recognition independent of translation using the self-made ultrasonic sensor fabricated with porous piezoelectric resonator and presented. The sensor was satisfied with requirement of ultrasonic sensor. The recognition rates for the training data and the testing data are 97.45 and 91.25[%] respectively using the self-made ultrasonic sensor and SCL(Simple Competitive Learning) neural network. According to the experimental results It is believed that the self-made ultrasonic sensor can be applied as sensor of SONAR system.

• 한국재료학회지
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• 제18권6호
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• pp.289-293
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• 2008

Porous HAp with three-dimensional network channels was prepared in a polymer foam process using a in-situ formation. HAp/polyol with various HAp solid contents was formed with an addition of isocyanate. Under all conditions, the obtained porous HAp had pore sizes ranging $50\;{\mu}m$ to $250\;{\mu}m$. The influence of the HAp content on the physical and mechanical properties of porous HAp scaffolds was investigated. As the solid content increased, the porosity of the porous HAp decreased from 79.3% to 77.9%. On the other hand, the compressive strength of the porous HAp increased from 0.7 MPa to 3.7 MPa. With a HAp solid content of 15 g, the obtained porous HAp had physical properties that were more suitable for scaffolds compared to other conditions.

• 방사성폐기물학회지
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• 제4권1호
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• pp.9-15
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• 2006

결정질 암반에 위치한 가상의 방사성폐기물처분장에 대한 정확한 안전성 평가를 수행하기 위해서는 다공암반으로 대표되는 공학방벽 및 결정질 암반으로 대표되는 자연방벽을 모두 고려한 매질에서의 물질 거동 특성을 정확하게 모사하는 것이 중요하다. 본 논문에서는 단열-다공암반내 유동 및 물질전달의 정확한 해석을 위한 연결망 구축방법에 대하여 서술하였다. 실제 단열암반을 사실적으로 모사하기 위하여 단열 물성자료는 확률밀도함수를 이용하여 생성하였다. 2차원의 사각격자로 모사된 단열암반과 육면체로 모사된 다공암반간 교차선의 원활한 검색을 위하여 단열암반과 연결전 다공암반의 교차면에 가상의 단열암반을 추가적으로 도입하였다. 전체유동경로를 구성하기 저하여 생성된 단열들 간의 교차선을 효율적으로 검색할 수 있는 방법 및 단열암반 및 단열-다공암반간의 연결도를 신속히 확인하는 알고리즘을 제안하였다. 이러한 방법들은 추후 방사성폐기물처분장에서의 단열-다공 암반을 통한 핵종 이동 특성을 모사할 수 있는 수치코드 개발에 많은 도움을 줄 것으로 사료된다.

• 한국결정성장학회:학술대회논문집
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• 한국결정성장학회 1996년도 The 9th KACG Technical Annual Meeting and the 3rd Korea-Japan EMGS (Electronic Materials Growth Symposium)
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• pp.494-496
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• 1996

The purpose of this study is to investigate the effect of process conditions on pore distribution in porous silicon layer prepared by electrochemical reaction. Porous silicon layers formed on p-type silicon wafer show the network structure of fine porse whose diameters are less than 100${\AA}$. In n-type porous silicon, selective growth was found on the pore surface by wet etching process after PR patterning. And numerical method showed high current density on the pore tip. With this result we confirmed that pore formation has two steps. First step is the initial attack on the surface and second step is the directional growth on the pore tip.

• 한국세라믹학회지
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• 제40권12호
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• pp.1159-1164
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• 2003

Two processing routes (i.e., the gel casting and polymer preform routes) using polymer beads were studied to fabricate porous ceramics with a cellular structure. The gel casting route, comprising the gel casting of a ceramic slurry mixed with polymer beads, was found to be inadequate to produce porous ceramic bodies with a interconnected pore structure, due to complete coating of the slurry on the polymer beads, which left just isolated pores in the final sintered bodies. The polymer preform route, involving the infiltration of a polymer beads preform with the ceramic slurry, successfully produced porous ceramics with a highly interconnected network of spherical pores. The pore size of 250-300 $\mu\textrm{m}$ was demonstrated and the porosity ranged from 82 to 86%. This process is advantageous to control the pore size because it is determined by the sizes of polymer beads used. Another feature is the avoidance of hollow skeleton, giving a high strength.