• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2008년도 추계학술대회A
• /
• pp.622-624
• /
• 2008

This investigation studies the effects of material properties and corresponding propagation wave types on optimal configurations of sound absorbing porous materials in maximizing the absorption performance by topology optimization. The acoustic behavior of porous materials is characterized by their material properties which determine motions of the frame and the air. When the frame has a motion, two types of compressional wave propagate in the porous material. Because each wave in the material make different influence on the absorption performance, it is important to understand the relative contribution of each wave to the sound absorption. The relative contribution of the propagating waves in a porous material is determined by the material properties, therefore, an optimal configuration of a porous material to maximize the absorption performance is apparently affected by the material properties. In fact, virtually different optimal configurations were obtained for absorption coefficient maximization when the topology optimization method developed by the authors was applied to porous materials having different material properties. In this investigation, some preliminary results to explain the findings are presented. Although several factors should be considered, the present investigation is focused on the effects of the material properties and corresponding propagation waves on the optimized configurations.

• 한국세라믹학회지
• /
• 제41권1호
• /
• pp.19-23
• /
• 2004

The Hertzian indentation contact damage behavior of porous alumina with controlled pore shape was investigated by experiments. Porous alumina ceramics containing well-defined pore shape, size and distribution were prepared by incorporation of fugitive spherical starch. Porous alumina with isolated pore structure was prepared with porosity range up to 30%. The indentation stress-strain curves of porous alumina were constructed. Elastic modulus and yield stress can be obtained from the stress-strain relationship. Impulse excitation method for the measurement of elastic modulus was also conducted as well as Hertzian indentation and was confirmed as a useful tool to evaluate the elasticity of highly porous ceramics. Elastic modulus of the inter-connected pore structure is more sensitive to porosity than that of the isolated pore structure. When the specimen had isolated pore structure, higher yield point was obtained than it had inter-connected pore structure. This study proposed that the elastic modiulus of porous ceramics is strongly related to not only porosity, but also the structure of pore.

• 한국소음진동공학회:학술대회논문집
• /
• 한국소음진동공학회 2005년도 추계 학술대회논문집(수송기계편)
• /
• pp.118-121
• /
• 2005

The acoustical performance of porous materials is determined by their seven or more macroscopic physical properties. However, it is not easy to measure all these properties in many cases. Furthermore, the measurement is compels engineers to spend much times. The effect of each property on the normal incidence absorption coefficient and normalized surface impedance was studied to estimate the properties of porous materials by numerical method. According to the investigation, Properties of porous materials are divided into several groups and estimated by each group. This paper is focused on the estimation procedure of porous materials by the numerical method.

• 한국분말재료학회지
• /
• 제22권2호
• /
• pp.122-128
• /
• 2015

In this study, titanium(Ti) meshes and porous bodies are employed to synthesize carbon nanotubes(CNTs) using methane($CH_4$) gas and camphene solution, respectively, by chemical vapor deposition. Camphene is impregnated into Ti porous bodies prior to heating in a furnace. Various microscopic and spectroscopic techniques are utilized to analyze CNTs. It is found that CNTs are more densely and homogeneously populated on the camphene impregnated Ti-porous bodies as compared to CNTs synthesized with methane on Ti-porous bodies. It is elucidated that, when synthesized with methane, few CNTs are formed inside of Ti porous bodies due to methane supply limited by internal structures of Ti porous bodies. Ti-meshes and porous bodies are found to be multi-walled with high degree of structural disorders. These CNTs are expected to be utilized as catalyst supports in catalytic filters and purification systems.

• 한국재료학회지
• /
• 제11권10호
• /
• pp.895-899
• /
• 2001

Electrical properties of porous $BaTiO_3-based$ ceramics were investigated from the viewpoint of adsorbed oxygen. Namely, the effects of heat-treatment temperature ($450-600^{\circ}C$) and measuring atmosphere (oxygen and nitrogen) on the PTCR characteristics of the porous $BaTiO_3-based$ ceramics were investigated. It was found that the PTCR characteristics of the porous $BaTiO_3-based$ ceramics was developed at $\geq$55$0^{\circ}C$, and the magnitude of the PTCR characteristics increased with increasing heat-treatment temperature. It was also found that the magnitude of the PTCR characteristics in the porous $BaTiO_3-based$ ceramics increased in oxygen atmosphere, whereas decreased in nitrogen atmosphere during heating and cooling.

• 한국재료학회지
• /
• 제16권11호
• /
• pp.715-718
• /
• 2006

Porous hydroxyapatite (HAp) scaffolds have been prepared by using the slurry including HAp and magnesia based on the replication of polymer sponge substrate. The influence of MgO content in slurry on the pore morphology and size, density, porosity, and mechanical strength of porous HAp scaffolds was investigated. The obtained scaffolds with average pore sizes ranging 150 to 300 mm had open, relatively uniform, and interconnected porous structure regardless of MgO content. As the MgO content increased, the pore network frame of scaffolds became to be relatively stronger, even though the pore size was not much changed. The compressive strength of the scaffolds increased rapidly with the increase of MgO content because of increasing the pore wall thickness and density of the scaffolds. As a result, the porosity, density, and compressive strength of the porous HAp scaffolds prepared by the sponge method were significantly affected by the addition of MgO.

• 한국전기전자재료학회논문지
• /
• 제23권10호
• /
• pp.814-819
• /
• 2010

Porous carbon electrodes with wooden materials are manufactured by molding carbonized wood powder. Electrical properties of the interface for electrolyte and porous carbon electrode are investigated from viewpoint of NaCl electrolyte concentration, capacitance and complex impedance. Density of porous carbon materials is 0.47~0.61 g/$cm^3$. NaCl electrolytic absorptance of the porous carbon materials is 5~30%. As the electrolyte concentration increased, capacitance is increased and electric resistance is decrease with electric double layer effect of the interface. The electric current of the porous carbon electrode compared in the copper and the high density carbon electrode was improved on a large scale, due to a increase in surface area. The circuit current increased as the distance between of the porous carbon electrode and the zinc electrode decreased, due to increase in electric field. Experimental results indicated that the current properties of galvanic cell could be improved by using porous carbon electrode.

• 한국미생물·생명공학회지
• /
• 제30권1호
• /
• pp.73-78
• /
• 2002

4 종류의 무기담채와 지렁이 분변토를 담채로 사용하여 분변토 집식배양한 질산화 세균을 접종한 바이오필터의 암모니아 제거 특성을 규명하였다. 담채의 암모니아 흡착능은 zcocarbn(24g-NH3/kg)을 제외하고 무시할 수준이었으며, 충전부피 당 담체의 미생물 고정화량은 담채 종류와 관계없이 유사하였다. 바이오필터의 압력손실은 분변토 $\geq$ zeocarbon $\geq$ zeolite $\geq$ porous glass $\simeqporous $ 순이었다. 담체의 충전 부피를 기준으로 한 최대 제거용량($g-Nkg^{-1}$$d^{-1}$)은 zeocarbon (526) $\geq$ 분변토 (220) $\geq$ porous celite (93) > Zeolite (68) > porous glass (53) 순으로 바이오필터의 성능은 담체에 많은 영향을 받는 것을 확인할 수 있었다. 속도론적 해석에 의해 $V_{m}$과 $K_{s}$를 구하였으며, 담체들간의 암모니아 제거 성능을 고려할 때 가장 우수한 담체는 zeocarbon 이었다.

• 한국소음진동공학회:학술대회논문집
• /
• 한국소음진동공학회 2002년도 추계학술대회논문집
• /
• pp.896-901
• /
• 2002

The sound absorption coefficients for multiple layer perforated plate systems containing several compartments with airspaces and porous absorbing materials are estimated using the transfer matrix method developed in the previous paper. The absorption coefficients from transfer matrix method agree well with the values measured by the two-microphone impedance tube method for various combinations of perforated plates, airspaces or porous materials. Based on these results, a guidance for the design of multiple layer perforated plate systems combined with airspaces and porous absorbing materials is discussed in detail.

• 한국세라믹학회지
• /
• 제50권6호
• /
• pp.429-433
• /
• 2013

Silicon, carbon, and B4C powders were used as raw materials for the fabrication of porous SiC. ${\beta}$-SiC was synthesized at $1500^{\circ}C$ in an Ar atmosphere from a silicon and carbon mixture. The synthesized powders were pressed into disk shapes and then heated at $2100^{\circ}C$. ${\beta}$-SiC particles transformed to ${\alpha}$-SiC at over $1900^{\circ}C$, and rapid grain growth of ${\alpha}$-SiC subsequently occurred and a porous structure with elongated plate-type grains was formed. The mechanism of this rapid grain growth is thought to be an evaporation-condensation reaction. The mechanical properties of the fabricated porous SiC were investigated and discussed.