• Advances in nano research
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• 제13권3호
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• pp.247-257
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• 2022

Extraordinary properties of nanocomposites make them a primary replacement for many conventional materials. Anterior cruciate ligament (ACL) reconstruction, which is a frequent surgery in sport activities, is one of the fields in which nanocomposites could be utilized. In the present study, the mechanical properties of different porous scaffolds made from graphene nano-composites are presented ad load bearing capacity of these materials is calculated using finite element method. The numerical results are further compared with experimental published data. In addition, several geometrical and material parameters are analyzed to find the best configuration of nanocomposite scaffolds in reconstruction of ACL. Moreover, coating of detoxification chemicals are extremely easier on the nano-structured materials than conventional one. Detoxification potential of nano-composites in the injured body are also discussed in detail. The results indicated that nano-composite could be successfully used in place of auto- and allografts and also instead of conventional metallic screws in reconstruction of ACL.

• Journal of Electrochemical Science and Technology
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• 제2권4호
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• pp.204-210
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• 2011

Thin film electrodes have been intensively studied for active materials and current collectors to enhance the electrochemical performance. Here, porous structures of nickel-based oxide films, consisting of nickel oxide and copper (II) oxide, which was derived from the copper substrate during the annealing process, were deposited on metallic copper foils. The half-cell tests revealed excellent capacity retention after $80^{th}$ charge/discharge cycles. Some films showed an excess of the theoretical capacity of nickel oxides, which mainly originate from partially oxidized copper substrates during annealing. These results exhibit that both a preparation method of an active materials and partially oxidized current collectors could be important roles to apply thin film electrodes.

• 한국세라믹학회지
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• 제51권4호
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• pp.231-242
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• 2014

An interconnect in solid oxide fuel cells (SOFCs) electrically connects unit cells and separates fuel from oxidant in the adjoining cells. The interconnects can be divided broadly into two categories - ceramic and metallic interconnects. A thin and gastight ceramic layer is deposited onto a porous support, and metallic interconnects are coated with conductive ceramics to improve their surface stability. This paper provides a short review on ceramic materials for SOFC interconnects. After a brief discussion of the key requirements for interconnects, the article describes basic aspects of chromites and titanates with a perovskite structure for ceramic interconnects, followed by the introduction of dual-layer interconnects. Then, the paper presents protective coatings based on spinel-or perovskite-type oxides on metallic interconnects, which are capable of mitigating oxide scale growth and inhibiting Cr evaporation.

• 한국분말재료학회지
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• 제19권6호
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• pp.446-450
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• 2012

In order to fabricate the porous Mo with controlled pore characteristics, unique processing by using $MoO_3$ powder as the source and camphene as the sublimable material is introduced. Camphene-based 15 vol% $MoO_3$ slurries, prepared by milling at $50^{\circ}C$ with a small amount of dispersant, were frozen 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 $750^{\circ}C$, and sintered at $1000-1100^{\circ}C$ for 1 h. After heat treatment in hydrogen atmosphere, $MoO_3$ powders were completely converted to metallic W without any reaction phases. The sintered samples showed large pores with the size of about $150{\mu}m$ 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 due to the difference in the camphene growth rate during freezing process. The size of small pores was decreased with increase in sintering temperature, while that of large pores was unchanged. The results are strongly suggested that the porous metal with required pore characteristics can be successfully fabricated by freeze-drying process using metal oxide powders.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2000년도 추계학술대회논문집
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• pp.396-402
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• 2000

Porous structures of aluminum foam have been studied. The apparent foam shape, foam hight, density, pore size, shape, and their distributions in various section areas of the experimental samples have been investigated. The sample have been cast into metallic mold, using aluminum foam prepared from a precursor based on pure Al ingot mixed with various amount of 1-2wt% increasing viscosity and foam agent materials. The process provides for flexibility in design of foam structures via relatively easy control over the amount of hydrogen evolution and the drainage processes which occur during foam formation. This is facilitated by manupulating parameters such as the foaming agent, thermal histories during solidification and mix melt viscosities. The acoustical performance of the panel made with the foamed aluminum is considerably improved; its absorption coefficient shows NRC 0.6-0.8. It has been found that the Al foam is very preferable for the compactness of the thermal system.

• 공업화학
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• 제24권4호
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• pp.438-442
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• 2013

본 연구에서는 무전해 도금법으로 니켈과 인을 탄소섬유 표면에 코팅한 후, 열처리시키는 과정에서 일어나는 변화를 다양한 분석방법을 이용하여 연구하였다. 전자현미경(Scanning Electron Microscopy, SEM)을 이용한 연구에서는, 코팅 후 추가적인 열처리를 하지 않은 경우 평평한 표면구조를 관찰하였으나, 열처리 온도가 $350^{\circ}C$에 이르면서 다공성구조가 생성됨을 알았다. 열처리 온도를 $50^{\circ}C$ 간격으로 증가시키면서 연구한 결과 $650^{\circ}C$까지는 열처리 온도가 증가할수록 기공의 크기는 증가하고, 개수는 감소하는 경향성이 관찰되었다. X-선 회절법(x-ray diffraction, XRD) 측정 결과, 코팅 후 추가 열처리가 없는 경우 금속성 Ni, Ni-P 화합물이 관찰되었으며, 열처리 온도가 증가함에 따라 NiO 봉우리는 세기가 증가하며, 금속성 Ni 봉우리의 세기는 감소하였다. X-선 광전자 분광법(X-ray Photoelectron Spectroscopy, XPS) 측정에서는 $650^{\circ}C$, $700^{\circ}C$의 열처리 후 인 산화물이 표면에서 검출됨을 확인하였는데, 이는 코팅된 니켈 필름의 내부에 존재하던 인 화합물이 열처리 온도가 증가함에 따라서 표면 밖으로 빠져 나오는 현상이 일어나는 결과로 해석할 수 있다. 이상의 분석 데이터를 토대로, 무전해 도금으로 코팅된 Ni-P 화합물($Ni_xP_y$)이 열처리 과정에서 산화되면서, 이때 생성된 인 화합물 기체가 승화하면서 필름에 기공을 생성시키는 것으로 제안할 수 있다. 다공성 물질은 넓은 비표면적 등의 우수한 물성때문에 불균일 촉매 등 다양한 분야에 적용될 수 있으며, 본 연구에서 소개하는 다공성 니켈 필름의 제작법은 대량 생산에 적용이 쉬워 환경 필터 분야 등의 다양한 곳에 응용될 수 있을 것으로 생각된다.

• 한국재료학회지
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• 제26권5호
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• pp.250-257
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• 2016

Octahedral $Co_3O_4$/carbon nanofiber (CNF) composites are fabricated using electrospinning and hydrothermal methods. Their morphological characteristics, chemical bonding states, and electrochemical properties are used to demonstrate the improved photovoltaic properties of the samples. Octahedral $Co_3O_4$ grown on CNFs is based on metallic Co nanoparticles acting as seeds in the CNFs, which seeds are directly related to the high performance of DSSCs. The octahedral $Co_3O_4$/CNFs composites exhibit high photocurrent density ($12.73mA/m^2$), superb fill factor (62.1 %), and excellent power conversion efficiency (5.61 %) compared to those characteristics of commercial $Co_3O_4$, conventional CNFs, and metallic Co-seed/CNFs. These results can be described as stemmnig from the synergistic effect of the porous and graphitized matrix formed by catalytic graphitization using the metal cobalt catalyst on CNFs, which leads to an increase in the catalytic activity for the reduction of triiodide ions. Therefore, octahedral $Co_3O_4$/CNFs composites can be used as a counter electrode for Pt-free dye-sensitized solar cells.

• 소성∙가공
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• 제11권8호
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• pp.701-709
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• 2002

Aluminium foam material is highly porous material, which has the complicated cellular structure defined by randomly distributed pores in metallic matrix. This structure gives the characteristic properties which cannot be achieved by any other conventional processes. As the properties of aluminium foam material significantly depend on its porosity, a desired profile of properties can be tailored by changing the foam density. But various defects lead to undesirable effects on the mechanical properties. Mechanical properties are dependent on cell sizes and aspect ratios. Therefore, this paper presents the effects of various processing parameters of various parameters on the mechanical properties. For the sake of this, combined stirring was used to fabricate aluminum foam materials by the parameters. Compression and bending tests were performed to investigate the effects of cell sizes and aspect ratios on the mechanical properties.

• Journal of Industrial and Engineering Chemistry
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• 제67권
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• pp.347-357
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• 2018

Steady shear response of a magnetorheological fluid (MRF) system containing porous mono-disperse magnetite ($Fe_3O_4$) spheres synthesized by solvothermal method is demonstrated. In applied magnetic field the interaction between the spherical particles leads to form strong columnar structures enhancing the yield strength and viscosity of the MRFs. The yield strengths of the MRFs also scale up with the concentration of magnetic particles in the fluid. Considering magnetic dipolar interaction between the particles the magneto-mechanical response of the MRFs is explained. Unlike metallic iron particles, the low-density corrosion resistant soft-ferrimagnetic $Fe_3O_4$ spherical particles make our studied MRF system efficient and reliable for shock-mitigation/vibration-isolation applications.

• 한국분말재료학회지
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• 제14권6호
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• pp.362-366
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• 2007

Magnesium and magnesium alloys are promising materials for light weight and high strength applications. In order to obtain homogeneous and high quality products in powder compaction and powder forging processes, it is very important to control density and density distributions in powder compacts. In this study, a model for densification of metallic powder is proposed for pure magnesium. The mode] considers the effect of powder characteristics using a pressure-dependent critical density yield criterion. Also with the new model, it was possible to obtain reasonable physical properties of pure magnesium powder using cold iso-state pressing. The proposed densification model was implemented into the finite element method code. The finite element analysis was applied to simulating die compaction of pure magnesium powders in order to investigate the density and effective strain distributions at room temperature.