• 한국기계가공학회지
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• 제11권1호
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• pp.62-67
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• 2012

Recently UV laser is widely used to process micro parts using various materials such as polymers, metals and ceramics because it has a very high intensity at the focused spot area. It is generally known that there are still some difficulties for alumina($Al_2O_3$) ceramics to directly make micro patterns like holes and lines on the surface of working material using 355nm UV laser because the alumina has a very low absorption coefficient at that wavelength. But nowadays new alumna with nano-porous holes is developed and applied to advanced micro functional parts of IT, BT and BT industries. In this paper, we are going to show the mechanism of photo-thermal ablation for nano-porous ceramics. Inside hole there is a lot of multiple reflections along the depth of hole. Experimentally we can find the micro hole drilling and micro grooving on the surface of nano-porous alumina.

• 대한치과보철학회지
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• 제46권3호
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• pp.307-319
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• 2008

STATEMENT OF PROBLEM: It is known that an anodic oxidation technique, one of the methods for the implant surface treatment, remarkably increased surface area, enhanced wettability and accelerated the initial bone healing. Purpose: This study was performed to evaluate the wettability of anodized titanium surface which has a nanotubular structure, to assess osseointegration after the placement of implant with nano-size tubes on tibia of rats and to analyze quantitatively transferable rhBMP-2 on each surface. MATERIAL AND METHOD: Four different kinds of surface-treated titanium discs (polished (machined surface) group, micro (blasting surface) group, nano (anodizedmachined surface) group, and nano-micro (anodized-blasting surface) group) were fabricated (n=10). Three different media were chosen to measure the surface contact angles; distilled water, plasma and rhBMP-2 solution. After a single drop (0.025 $m{\ell}$) of solution, the picture was taken with the image camera, and contact angle was measured by using image analysis system. For the test of osseointegration, 2 kinds of anodized surface (anodized-machined surface, anodized-blasting surface) implants having 2.0 mm in diameter and 5.0 mm in length inserted into the tibia of Wistar rats. After 3 weeks, tibia were harvested and the specimens were stained with hematoxylin and eosin for histological analysis. To test the possibility of drug delivery, after soaking sample groups in the concentration of 250 ng/$m{\ell}$l of rhBMP-2 for 48 hours, the excess solution of rhBMP-2 were removed. After that, they were lyophilized for 24 hours, and then the rhBMP-2 on the surface of titanium was resolved for 72 hours in PBS. All the extracted solution was analyzed by ELISA. One-way analysis of variance (ANOVA) was performed on the data. RESULTS: The wettability is improved by anodic oxidation. The best wettability was shown on the nano-micro group, and it was followed by nano group, micro group, and polished group. In the histological findings, all implants showed good healing and the new bone formation were observed along the implant surface. After 3 days, nano-micro group delivered the most amount of rhBMP-2, followed by nano group, micro group, and polished group. CONCLUSION: It indicated that anodic oxidation on blasting surface produce functionally graded nano-micro porous structure and enhance hydrophilicity of the surface and osseointegration. The findings suggest that the nano-micro porous structure could be a useful carrier of osteogenic molecules like rhBMP-2.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2009년도 제40회 하계학술대회
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• pp.1539_1540
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• 2009

본 논문에서는 Porous Au-Pt 전극을 기반으로 연료전극과 공기전극으로 구성된 초소형 메탄올 센서를 설계 및 제작하고 그 특성을 분석해 보았다. 제안된 Porous Au-Pt 전극은 Porous 구조의 금속을 만드는 방법 중 하나인 Templating기법을 적용하여 수백나노 크기의 Pore들을 가진 Porous Au 전극을 제작하였고 그 위에 수 나노 크기의 Pt particles을 전해 도금하여 제작되었다. 고분자 전해질막 층으로서 Nafion film은 전해 도금한 Porous Au-Pt 전극 사이에 삽입하고 hot Pressing 통하여 센서를 구성하였다. Porous Au-Pt 전극을 기반으로한 전기화학 메탄올 센서는 $0.25\;cm^2$ 의 작은 전극 면적에도 불구하고 넓은 온도 범위 ($20^{\circ}C-100^{\circ}C$) 에서 온도에 따른 뛰어난 선형성(Correlation coefficient = 0.986)을 보였으며, 특히, 일정온도 ($60^{\circ}C$)에서 메탄올 농도 0 M에서 2 M 까지의 전류응답 특성을 측정, 분석 결과 메탄올 농도에 따른 9.6 mA/$mM{\cdot}cm^2$ 의 민감도 및 10 초 이내의 응답시간 특성을 보였다.

• Interaction and multiscale mechanics
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• 제4권2호
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• pp.107-122
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• 2011

Mechanical behavior in nano-sized structures differs from those in macro sized structures due to surface effect. As the ratio of surface to volume increases, surface effect is not negligible and causes size-dependent mechanical behavior. In order to identify this size effect, atomistic simulations are required; however, it has many limitations because too much computational resource and time are needed. To overcome the restrictions of the atomistic simulations and graft the well-established continuum theories, the continuum model considering surface effect, which is based on the bridging technique between atomistic and continuum simulations, is introduced. Because it reflects the size effect, it is possible to carry out a variety of analysis which is intractable in the atomistic simulations. As a part of the application examples, the homogenization method is applied to micro/nano thin films with porosity and the homogenized elastic coefficients of the nano scale thickness porous films are computed in this paper.

• 한국세라믹학회지
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• 제43권11호
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• pp.746-750
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• 2006

NiO films and Ru co-sputtered NiO films were deposited by reactive magnetron sputtering for micro-solid oxide fuel cell anode applications. The deposited films were reduced to form porous films. The reduction kinetics of the Ru doped NiO film was more sluggish than that of the NiO film, and the resulting microstructure of the former exhibited finer pore networks. The possibility of using the films for the anodes of single chamber micro-SOFCs was investigated using an air/fuel mixed environment. It was found that the abrupt increase in the resistance is suppressed in the Ru co-sputtered film, as compared to undoped film.

• Advances in nano research
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• 제8권1호
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• pp.69-82
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• 2020

In this study, the free and forced vibration analysis of micro sandwich plate with porous core layer and magneto-electric face sheets based on modified couple stress theory and first order shear deformation theory under simply supported boundary conditions is illustrated. It is noted that the core layer is composed from balsa wood and also piezo magneto-electric facesheets are made of BiTiO₃-CoFe₂O₄. Using Hamilton's principle, the equations of motion for micro sandwich plate are obtained. Also, the Navier's method for simply support boundary condition is used to solve these equations. The effects of applied voltage, magnetic field, length to width ratio, thickness of porous to micro plate thickness ratio, type of porous, coefficient of porous on the frequency ratio are investigated. The numerical results indicate that with increasing of the porous coefficient, the non-dimensional frequency increases. Also, with an increase in the electric potential, the non-dimensional frequency decreases, while and with increasing of the magnetic potential is vice versa.

• Computers and Concrete
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• 제24권3호
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• pp.185-192
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• 2019

In this paper, the buckling of micro sandwich hollow circular plate is investigated with the consideration of the porous core and piezoelectric layer reinforced by functionally graded (FG)carbon nano-tube. For modeling the displacement field of sandwich hollow circular plate, the high-order shear deformation theory (HSDT) of plate and modified couple stress theory (MCST) are used. The governing differential equations of the system can be derived using the principle of minimum potential energy and Maxwell's equation that for solving these equations, the Ritz method is employed. The results of this research indicate the influence of various parameters such as porous coefficients, small length scale parameter, distribution of carbon nano-tube in piezoelectric layers and temperature on critical buckling load. The purpose of this research is to show the effect of physical parameters on the critical buckling load of micro sandwich plate and then optimize these parameters to design structures with the best efficiency. The results of this research can be used for optimization of micro-structures and manufacturing different structure in aircraft and aerospace.

• 한국재료학회지
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• 제22권1호
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• pp.1-7
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• 2012

Thin film electrode consisting purely of porous anodic tin oxide with well-defined nano-channeled structure was fabricated for the first time and its electrochemical properties were investigated for application to an anode in a rechargeable lithium battery. To prepare the thin film electrode, first, a bi-layer of porous anodic tin oxides with well-defined nano-channels and discrete nano-channels with lots of lateral micro-cracks was prepared by pulsed and continuous anodization processes, respectively. Subsequent to the Cu coating on the layer, well-defined nano-channeled tin oxide was mechanically separated from the specimen, leading to an electrode comprised of porous tin oxide and a Cu current collector. The porous tin oxide nearly maintained its initial nano-structured character in spite of there being a series of fabrication steps. The resulting tin oxide film electrode reacted reversibly with lithium as an anode in a rechargeable lithium battery. Moreover, the tin oxide showed far more enhanced cycling stability than that of powders obtained from anodic tin oxides, strongly indicating that this thin film electrode is mechanically more stable against cycling-induced internal stress. In spite of the enhanced cycling stability, however, the reduction in the initial irreversible capacity and additional improvement of cycling stability are still needed to allow for practical use.

• Advances in nano research
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• 제15권5호
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• pp.423-439
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• 2023

The aim of this paper is to investigate the free vibration behavior of the micro sandwich beam composing of five layers such as functionally graded (FG) porous core, nanocomposite reinforced by carbon nanotubes (CNTs) and piezomagnetic/piezoelectric layers subjected to magneto electrical potential resting on silica aerogel foundation. The effect of foundation has been taken into account using Vlasov model in addition to rigid base assumption. For this purpose, an iterative technique is applied. The material properties of the FG porous core and FG nanocomposite layers are considered to vary throughout the thickness direction of the beams. Based on the Timoshenko beam theory and Hamilton's principle, the governing equations of motion for the micro sandwich beam are obtained. The Navier's type solution is utilized to obtain analytical solutions to simply supported micro sandwich beam. Results are verified with corresponding literatures. In the following, a study is carried out to find the effects of the porosity coefficient, porous distribution, volume fraction of CNT, the thickness of silica aerogel foundation, temperature and moisture, geometric parameters, electric and magnetic potentials on the vibration of the micro sandwich beam. The results are helpful for the design and applications of micro magneto electro mechanical systems.

• Steel and Composite Structures
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• 제41권6호
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• pp.805-820
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• 2021

In this research, the buckling and free vibration of three-phase carbon nanotubes/ fiber/ polymer piezoelectric nanocomposite face sheet sandwich microbeam with microsensor and micro-actuator surrounded in elastic foundation based on modified couple stress theory (MCST) is investigated. Three types of porous materials are considered for sandwich core. Higher order (Reddy) and sinusoidal shear deformation beam theories are employed for the displacement fields. Sinusoidal surface stress effects are extracted for sinusoidal shear deformation beam theory. The equations of motion are derived by Hamilton's principle and then the natural frequency and critical buckling load are obtained by Navier's type solution. The determined results are in good agreement with other literatures. The detailed numerical investigation for various parameters is performed for this microsensor-microactuator. The results reveal that the microsensor-microactuator enhanced by increasing of Skempton coefficient, carbon nanotubes diameter length to thickness ratio, small scale factor, elastic foundation, surface stress constants and reduction in porous coefficient, micro-actuator voltage and CNT weight fraction. The valuable results can be expedient for micro-electro-mechanical (MEMS) and nano-electro-mechanical (NEMS) systems.