• Geomechanics and Engineering
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• 제37권1호
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• pp.85-95
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• 2024

This study investigates the influence of nano-silica and basalt fiber content, curing duration, and freeze-thaw cycles on the static and dynamic properties of soil specimens. A comprehensive series of tests, including Unconfined Compressive Strength (UCS), static triaxial, and dynamic triaxial tests, were conducted. Additionally, scanning electron microscopy (SEM) analysis was employed to examine the microstructure of treated specimens. Results indicate that a combination of 1% fiber and 10% nano-silica yields optimal soil enhancement. The failure patterns of specimens varied significantly depending on the type of additive. Static triaxial tests revealed a notable reduction in the brittleness index (IB) with the inclusion of basalt fibers. Specimens containing 10% nano-silica and 1% fiber exhibited superior shear strength parameters and UCS. The highest cohesion and friction angle were obtained for treated specimens with 10% nano-silica and 1% fiber, 90 kPa and 37.8°, respectively. Furthermore, an increase in curing time led to a significant increase in UCS values for specimens containing nano-silica. Additionally, the addition of fiber resulted in a decrease in IB, while the addition of nano-silica led to an increase in IB. Increasing nano-silica content in stabilized specimens enhanced shear modulus while decreasing the damping ratio. Freeze-thaw cycles were found to decrease the cohesion of treated specimens based on the results of static triaxial tests. Specimens treated with 10% nano-silica and 1% fiber experienced a reduction in shear modulus and an increase in the damping ratio under freeze-thaw conditions. SEM analysis reveals dense microstructure in nano-silica stabilized specimens, enhanced adhesion of soil particles and fibers, and increased roughness on fiber surfaces.

• 한국기계가공학회지
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• 제17권4호
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• pp.39-46
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• 2018

Two surfaces that have relative motion show different characteristics according to surface roughness or surface patterns in all lubrication areas. For two rough surfaces with mixed lubrication, this paper proposes a new approach that includes the contact characteristics of the surfaces and a probabilistic method for a numerical analysis of lubrication. As the contact area of the two surfaces changes according to the loading conditions, asperity contact is very important. An average flow model developed by Patir-Cheng is central to the study of lubrication for rough surfaces. This average flow model also refers to a multi-asperity contact model for deriving a modified Reynolds equation and calculating the lubricant characteristics of a bearing surface with random roughness during fluid flow. Based on the average flow model, this paper carried out a numerical analysis of lubrication using a contact model by considering a load change made by the actual contact of asperities between two surfaces. Lubrication properties show different characteristics according to the surface patterns. This study modeled various geometric surface patterns and calculated the characteristics of lubrication.

• Applied Microscopy
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• 제34권1호
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• pp.23-29
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• 2004

본 연구에서는 에너지 여과장치와 직접 고온 가열 장치를 이용하여 실리카 나노입자의 비정질 구조 분석과 가열실험을 통한 구조변화에 대해 연구하였다. 실리카 나노입자의 전자회절도형은 세 개의 diffuse한 ring으로 구성이 되어 있으며, $900^{\circ}C$의 온도에서 실리카 나노입자는 서서히 결정화가 이루어짐을 알 수가 있었다. 세 개의 diffuse한 ring은 비정질 실리카 구조가 $SiO_4$ tetrahedra가 구조의 기본 단위로 이루어졌으며, 가열에 의해 이들이 점이적으로 tridymite 이상적인 층상 구조로 결정화되어 간다는 것을 이해할 수 있었다. 또한 전자현미경 내의 고진공하에서 $850^{\circ}C$ 이상의 온도 가열로 인해 $SiO_2$로부터 증발된 SiO가 grid에 재증착되는 것을 관찰할 수 있었고, 남아 있는 $SiO_2$는 전기로를 이용한 가열 실험결과와 같이 비정질 구조에서 orthorhombic trydimite로의 결정화가 이루어짐을 알 수 있었다.

• Environmental Engineering Research
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• 제16권2호
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• pp.81-90
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• 2011

Different weight percentages of Ag, Pt, and Au doped nano $TiO_2$ were synthesized using the acetic acid hydrolyzed sol-gel method. The crystallite phase, surface morphology combined with elemental composition and light absorption properties of the doped nano $TiO_2$ were comprehensively examined using X-ray diffraction (XRD), $N_2$ sorption analysis, transmission electron microscopic (TEM), energy dispersive X-ray, and DRS UV-vis analysis. The doping of noble metals stabilized the anatase phase, without conversion to rutile phase. The formation of gold nano particles in Au doped nano $TiO_2$ was confirmed from the XRD patterns for gold. The specific surface area was found to be in the range 50 to 85 $m^2$/g. TEM images confirmed the formation a hexagonal plate like morphology of nano $TiO_2$. The photocatalytic activity of doped nano $TiO_2$ was evaluated using 4-chlorophenol as the model pollutant. Au doped (0.5 wt %) nano $TiO_2$ was found to exhibit higher photocatalytic activity than the other noble metal doped nano $TiO_2$, pure nano $TiO_2$ and commercial $TiO_2$ (Degussa P-25). This enhanced photocatalytic activity was due to the cathodic influence of gold in suppressing the electron-hole recombination during the reaction.

• 한국재료학회지
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• 제23권4호
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• pp.211-214
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• 2013

The effects of a Ni coating on the sensing properties of nano ZnO:Ni based gas sensors were studied for $CH_4$ and $CH_3CH_2CH_3$ gases. Nano ZnO sensing materials were prepared by the hydrothermal reaction method. The Ni coatings on the nano ZnO surface were deposited by the hydrolysis of zinc chloride with $NH_4OH$. The weight % of Ni coating on the ZnO surface ranged from 0 to 10 %. The nano ZnO:Ni gas sensors were fabricated by a screen printing method on alumina substrates. The structural and morphological properties of the nano ZnO : Ni sensing materials were investigated by XRD, EDS, and SEM. The XRD patterns showed that nano ZnO : Ni powders with a wurtzite structure were grown with (1 0 0), (0 0 2), and (1 0 1) dominant peaks. The particle size of nano ZnO powders was about 250 nm. The sensitivity of nano ZnO:Ni based sensors for 5 ppm $CH_4$ gas and $CH_3CH_2CH_3$ gas was measured at room temperature by comparing the resistance in air with that in target gases. The highest sensitivity of the ZnO:Ni sensor to $CH_4$ gas and $CH_3CH_2CH_3$ gas was observed at Ni 4 wt%. The response and recovery times of 4 wt% Ni coated ZnO:Ni gas sensors were 14 s and 15 s, respectively.

• 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.

• 한국자동차공학회논문집
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• 제20권5호
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• pp.19-25
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• 2012

This study describes effects of DME additives on combustion and exhaust emissions characteristics including nano-particle in a single cylinder compression ignition engine. Considered additives include bio-diesel, n-butanol, and MTBE for increasing kinematic viscosity. Among three additives, n-butanol showed the greatest kinematic viscosity. In addition MTBE showed the highest vapor pressure. In the present study mixing ratios of additives were kept constant at 1 and 10% by volume. Experiments were performed at 1200rpm engine speed and nano-particles were measured by SMPS (Scanning mobility particle sizer) devices. Results of combustion characteristics showed that considered additives had little effects on combustion pressure. However, patterns of heat release rate were dependent on properties of additives. Nano-particles of MTBE were the lowest among considered additives.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2006년도 춘계학술대회 논문집
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• pp.145-146
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• 2006

A fluorine-doped diamond-like carbon (F-DLC) stamp which has high contact angle, high UV-transmittance and sufficient hardness, was fabricated using the following direct etching method: F-DLC is deposited on a quartz substrate using DC and RF magnetron sputtering, PMMA is spin coated and patterned using e-beam lithography and finally, O2 plasma etching is performed to transfer the line patterns having 100 nm line width, 100 nm line space and 70 nm line depth on F-DLC. The optimum fluorine concentration was determined after performing several pre-experiments. The stamp was applied successfully to UV-NIL without being coated with an anti-adhesion layer.

• 한국기계가공학회지
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• 제13권4호
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• pp.7-12
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• 2014

A transparent poly methyl methacrylate (PMMA) optical micro-pyramid array-pattern is designed and fabricated using an injection modeling technique. The device's optical characteristics are tested and analyzed theoretically. In the optical pattern generated using the fabricated PMMA pattern, the components, due to not only refraction but also diffraction, are observed simultaneously. Wave optic modeling and analysis reveals that the energy ratio between the diffraction and refraction in the optical pattern are dependent on the critical dimension of the optical pattern such that the refraction and diffraction tend to be directly and inversely proportional to the pattern dimension, respectively.

• 한국전기전자재료학회논문지
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• 제34권4호
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• pp.242-245
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• 2021

In this work, we fabricated oxide on an n-type silicon substrate through local anodic oxidation (LAO) using atomic force microscopy (AFM). The resulting oxide thickness was measured and its correlation with load force, scan speed and applied voltage was analyzed. The surface oxide layer was stripped using a buffered oxide etch. Ohmic contacts were created by applying silver paste on the silicon substrate back face. LAO was performed at approximately 70% humidity. The oxide thickness increased with increasing the load force, the voltage, and reducing the scan speed. We confirmed that LAO/AFM can be used to create both lateral and, to some extent, vertical shapes and patterns, as previously shown in the literature.