• Journal of the Korean institute of surface engineering
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• v.54 no.5
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• pp.230-237
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• 2021

In this study, the influence of silicon contents on the microstructure, mechanical and tribological properties of Ti-Al-Si-N coatings were systematically investigated for application of cutting tools. The composition of the Ti-Al-Si-N coatings were controlled by different combinations of TiAl₂ and Ti₄Si composite target powers using an arc ion plating technique in a reactive gas mixture of high purity Ar and N₂ during depositions. Ti-Al-Si-N films were nanocomposite consisting of nanosized (Ti,Al,Si)N crystallites embedded in an amorphous Si₃N₄/SiO₂ matrix. The instrumental analyses revealed that the synthesized Ti-Al-Si-N film with Si content of 5.63 at.% was a nanocomposites consisting of nano-sized crystallites (5-7 nm in dia.) and a three dimensional thin layer of amorphous Si₃N₄ phase. The hardness of the Ti-Al-Si-N coatings also exhibited the maximum hardness value of about 47 GPa at a silicon content of ~5.63 at.% due to the microstructural change to a nanocomposite as well as the solid-solution hardening. The coating has a low friction coefficient of 0.55 at room temperature against an Inconel alloy ball. These excellent mechanical and tribological properties of the Ti-Al-Si-N coatings could help to improve the performance of machining and cutting tool applications.

• Design & Manufacturing
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• v.17 no.2
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• pp.55-61
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• 2023

With femtosecond (fs) laser pulse irradiation on metals, various types of nano- and micro-scale structures can be naturally induced at the surface through laser-matter interaction. Two notable structures are laser-induced periodic surface structures (LIPSSs) and cone/spike structures, which are known to significantly modify the optical and physical properties of metal surfaces. In this work, we irradiate fs laser pulses onto various types of metals, cold-rolled steel, pickled & oiled steel, Fe-18Cr-8Ni alloy, Zn-Mg-Al alloy coated steel, and pure Cu which can be useful for precise molding and imprinting processes, and adjust the morphological profiles of LIPSSs and cone/spike structures for clear structural coloration and a larger range of surface wettability control, respectively, by changing the fluence of laser and the speed of raster scan. The periods of LIPSSs on metals used in our experiments are nearly independent of laser fluence. Accordingly, the structural coloration of the surface with LIPSSs can be optimized with the morphological profile of LIPSSs, controlled only by the speed of the raster scan once the laser fluence is determined for each metal sample. However, different from LIPSSs, we demonstrate that the morphological profiles of the cone/spike structures, including their size, shape, and density, can be manipulated with both the laser fluence and the raster scan speed to increase a change in the contact angle. By injection molding and imprinting processes, it is expected that fs laser-induced surface structures on metals can be replicated to the plastic surfaces and potentially beneficial to control the optical and wetting properties of the surface of injection molded and imprinted products.

• Korean Chemical Engineering Research
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• v.61 no.2
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• pp.175-188
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• 2023

Global interest in hydrogen energy is increasing as an eco-friendly future energy that can replace fossil fuels. Accordingly, a next-generation hydrogen production technology using microorganisms, nuclear power, etc. is being developed, while a lot of time and effort are still required to overcome the cost of hydrogen production based on fossil fuels. As a way to minimize greenhouse gas emissions in the hydrocarbon-based hydrogen production process, methane direct decomposition technology has recently attracted attention. In order to improve the economic feasibility of the process, the simultaneous production of value-added carbon materials with hydrogen can be one of the most essential aspects. For that purpose, various studies on catalysis related to the quality and yield of high-value carbon materials such as carbon nanotubes (CNTs). In terms of process technology, a number of the research and development of fluidized-bed reactors capable of continuous production and improved gas-solid contact efficiency has been attempted. Recently, methane direct decomposition technology using a fluidized bed has been developed to the extent that it can produce 270 kg/day of hydrogen and 1000 kg/day of carbon. Plus, with the development of catalyst regeneration, separation and recirculation technologies, the process efficiency can be further improved. This review paper investigates the recent development of catalysts and fluidized bed reactor for methane direct pyrolysis to identify the key challenges and opportunities.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.26 no.1
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• pp.1-5
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• 2017

This study investigated the mechanical tearing of a cell membrane using a nanostructured alumina filter for easy and quick mechanical cell disruption. Nanostructured alumina filters were prepared by a multi-step aluminum anodizing process and nanopore etching process. Six different types of nanostructures were formed on the surface of the nanoporous alumina filters to compare the mechanical cell disruption characteristics according to the shape of the nanostructure. The prepared alumina filter was assembled in a commercial filter holder, and then, NIH3T3 fibroblast cells in a buffer solution were passed through the nanostructured alumina filter at a constant pressure. By measuring the concentration of proteins and DNA, the characteristics of mechanical cell disruption of the nanostructured alumina filter were investigated.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.25 no.1
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• pp.62-67
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• 2016

This paper presents a silicon nanostructure array embedded in a polymer film. The silicon nanostructure array was fabricated by using basic microelectromechanical systems (MEMS) processes such as photolithography, reactive ion etching, and anisotropic KOH wet etching. The fabricated silicon nanostructure array was transferred into polymer substrates such as polymethyl methacrylate (PMMA), polyethylene terephthalate (PET), and polycarbonate (PC) through the hot-embossing process. In order to determine the transfer conditions under which the silicon nanostructures do not fracture, hot-embossing experiments were performed at various temperatures, pressures, and pressing times. Transfer was successfully achieved with a pressure of 1 MPa and a temperature higher than the transition temperature for the three types of polymer substrates. The transferred silicon nanostructure array was electrically evaluated through measurements with a semiconductor parameter analyzer (SPA).

• 한국신재생에너지학회:학술대회논문집
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• 2011.05a
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• pp.79.1-79.1
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• 2011

인쇄전자 기술은 기존의 다양한 인쇄 공정에 전자 재료를 적용하여 전자소자 및 전자소자에 적용 가능한 제품들을 생산하는 기술이다. 인쇄 공정은 크게 접촉식과 비접촉식으로 구분할 수 있는데 비접촉식 인쇄 방식의 대표적인 예가 잉크젯과 스프레이 방식을 이용한 인쇄라고 할 수 있다. ESD는 정전기력을 이용한 스프레이 방식의 인쇄 공정으로써 기존의 정전기력만을 이용한 인쇄 방식과는 달리 정전기력과 공압을 동시에 적용하여 상대적으로 빠른 시간 내에 나노 박막의 코팅과 패터닝이 가능한 공정이다. 일반적으로 터치 패널에 사용되는 ITO의 경우는 증착 방식에 의존하고 있어 공정 시간이 길고 생산 단가도 비싸다는 단점이 있다. ESD 코팅의 경우는 기존의 증착 방식이 아닌 직접 인쇄 방식으로 공정 시간과 비용을 절감할 수 있는 장점이 있다. 투명 전도막 형성에 사용되는 전도성 고분자의 경우 ITO를 대체할 수 있을 만큼의 성능을 지니고 있어 터치 패널용 전극으로 응용할 수 있다. 따라서 본 논문에서는 ESD 공정을 이용하여 ITO 대체가 가능한 터치패널용 투명전극을 형성하였다. 전도성 고분자의 코팅 두께에 따라 전기적인 특성이 변화하지만 투과도 80%를 전후로 면저항이 $60{\sim}80{\Omega}/{\Box}$의 성능이 나타남을 확인할 수 있었다. 또한 코팅된 투명 전도막을 이용하여 터치패널용 모듈 제작을 통해 동작 여부도 확인할 수 있었다.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.24 no.4
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• pp.421-427
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• 2015

In this paper, a description is given of finite element method (FEM) simulations of the elastic bending modulus of multi-layered graphene sheets that were carried out to investigate the mechanical behavior of graphene sheets with different gap thicknesses through molecular mechanics theory. The interaction forces between layers with various gap thicknesses were considered based on the van der Waals interaction. A finite element (FE) model of a multi-layered rectangular graphene sheet was proposed with beam elements representing bonded interactions and spring elements representing non-bonded interactions between layers and between diagonally adjacent atoms. As a result, the average elastic bending modulus was predicted to be 1.13 TPa in the armchair direction and 1.18 TPa in the zigzag direction. The simulation results from this work are comparable to both experimental tests and numerical studies from the literature.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.24 no.5
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• pp.475-480
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• 2015

Ultrasonic atomic force microscopy (Ultrasonic-AFM) has been used to investigate the elastic property of the ultra-thin coating layer in a thin-film system. The modified Hertzian theory was applied to predict the contact resonance frequency through accurate theoretical analysis of the dynamic characteristics of the cantilever. We coat 200 nm thick Aluminum and Titanium thin films on the substrate using the DC Magnetron sputtering method. The amplitude and phase of the contact resonance frequency of a vibrating cantilever varies in response to the local stiffness constant. Ultrasonic-AFM images were obtained using the variations in the elastic property of the materials. The morphology of the surface was clearly observed in the Ultrasonic-AFM images, but was barely visible in the topography. This research demonstrates that Ultrasonic-AFM is a promising technique for visualizing the distribution of local stiffness in the nano-scale thin coatings.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.24 no.1
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• pp.135-139
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• 2015

We present a fine patterning method of conductive lines on polyimide (PI) and glass substrates using silver (Ag) nanoparticles based on laser scanning. Controlled laser irradiation can realize selective sintering of conductive ink without damaging the substrate. Thus, this technique easily creates fine patterns on heat-sensitive substrates such as flexible plastics. The selective laser sintering of Ag nanoparticles was managed by optimizing the conditions for the laser scan velocity (1.0-20 mm/s) and power (10-150 mW) in order to achieve a small gap size, high electrical conductivity, and fine roughness. The fabricated electrodes had a minimum channel length of $5{\mu}m$ and conductivity of $4.2{\times}10^5S/cm$ (bulk Ag has a conductivity of $6.3{\times}10^5S/cm$) on the PI substrate. This method was used to successfully fabricate an organic field effect transistor with a poly(3-hexylthiophene) channel.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.24 no.1
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• pp.94-97
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• 2015

In this study, we introduce a yellowing phenomenon in silver nanowire laser patterning and attempt to understand the cause of this phenomenon. Silver nanowire is a promising alternative to indium tin oxide as a transparent electrode owing to its flexibility. Additionally, silver nanowire can be easily patterned by laser ablation, which is free of dangerous chemicals. However, a yellowish color change reducing visibility is observed on the patterned area of the silver nanowires, and this yellowing phenomenon prevents the use of silver nanowire as a transparent electrode material. We concluded that resolidified debris of melted and evaporated silver nanowires after laser ablation causes the color change of the electrode. Further research is needed to determine a means of mitigating this yellowing phenomenon.