• Corrosion Science and Technology
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• v.21 no.4
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• pp.250-257
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• 2022

Transition metal sulfide materials have emerged as a new anode material for Li secondary batteries owing to their high capacity and rate capability facilitated by fast Li-ion transport through the layered structure. Among these materials, niobium disulfide (NbS₂) has attracted much attention with its high electrical conductivity and high theoretical capacity (683 mAh g^-1). In this study, we propose a facile synthesis of Fe_xNbS₂/C composite via simple ball milling and heat treatment. The starting materials of FeS and Nb were reacted in the first milling step and transformed into an Fe-Nb-S composite. In the second milling step, activated carbon was incorporated and the sulfide was crystallized into Fe_xNbS₂ by heat treatment. The prepared materials were characterized by X-ray diffraction, electron spectroscopies, and X-ray photoelectron spectroscopy. The electrochemical test results reveal that the synthesized Fe_xNbS₂/C composite electrode demonstrates a high reversible capacity of more than 600 mAh g^-1, stable cycling stability, and excellent rate performance for Li-ion battery anodes.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2002.02a
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• pp.53-60
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• 2002

Recently, the development of aerospace and automobile industries brought new technological challenges, related to the growing complexity of products and new geometry models. High speed machining using 5-Axis milling machine is widely used for 3D sculptured surface parts. 5-axis milling of turbine blade generates the vibration, deflection and twisting caused from thin and cantilever shape. So, the surface roughness and the waviness of workpiece are not good. In this paper, The effects of cutter orientation and lead/tilt angle in 5-Axis high speed ball end-milling of turbine blade were investigated to improve the geometric accuracy and surface integrity. The experiments were performed at lead/tilt angle $15^{\circ}$ of workpiece with four cutter directions such as horizontal outward, horizontal inward, vertical outward, and vertical inward. Workpiece deflection, surface roughness and machined surface were measured with various cutter orientations such as cutting direction, and lead/tilt angle. The results show that when 5-axis machining of turbine blade, the best cutting strategy is horizontal inward direction with tilt angle. The results show that when 5-axis machining of turbine blade, the best cutting strategy is horizontal inward direction with tilt angle.

• Transactions of Materials Processing
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• v.16 no.1 s.91
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• pp.15-19
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• 2007

This paper presents an integrated machining error compensation method based on captured images of tool deflection shapes in flat end-milling processes. This approach allows us to avoid modeling machining characteristics (cutting forces, tool deflections and machining errors etc.) and accumulating calculation errors induced by several simulations. For this, a high-speed camera captured images of real deformed tool shapes which were cutting under given machining conditions. Using image processes and a machining error model, it is possible to estimate tool deflection in cutting conditions modeled and to compensate for machining errors using an iterative algorithm correcting tool paths. This corrected tool path can effectively reduce machining errors in the flat end-milling process. Experiments are carried out to validate the approaches proposed in this paper. The proposed error compensation method can be effectively implemented in a real machining situation, producing much smaller errors.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.06a
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• pp.1640-1643
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• 2005

This paper presents analysis of dynamic characteristics of a high-speed milling spindle with a drawbar and a built-in motor. The spindle system with a built-in motor can be used to simplify the structure of machine tools, to improve the machining flexibility of machine tools, and to perform the high speed machining. In this system the shaft is usually assumed as a rigid rotor. In this paper, the modal characteristics of drawbar in high-speed milling spindle system due to supporting stiffness between drawbar and shaft and considering the mass and stiffness effects of the built-in motor's rotor are analyzed by numerical method. The result shows enough stiff supports must be provided between shaft and drawbar to prevent occurring drawbar vibration lower than the natural frequency of 1st bending mode of spindle. And considering the mass and stiffness of built-in motor's rotor is important thing to derive more accurate results.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2006.05a
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• pp.627-628
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• 2006

High speed milling process is emerging as an important fabrication process benefits include the ability to fabricate micro and meso-scale parts out of a greater range of materials and with more varied geometry. It also enables the creation of micro and meso-scale molds for injection molding. Factors affecting surface roughness have not been studied in depth for this process. A series of experiments has been conducted in order to begin to characterize the factors affecting surface roughness and determine the range of attainable surface roughness values for the high speed milling process. It has previously been shown that run-out creates a greater problem for the dimensional accuracy of pans created by high speed milling process. And run-out also has a more significant effect on the surface quality of milled parts. The surface roughness traces reveal large peak to valley variations. This run-out is generated by spindle dynamics and tool geometry. In order to investigate the relationship between tool alignment errors and surface roughness the scallop generating mechanism in the ball-end milling with tool alignement errors has been studied and simulated. The results indicate that tool alignment errors have no significant effects ell the dimension of scallops in for flat planes.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.23 no.2
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• pp.108-113
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• 2013

Chalcopyrite material $CuInSe_2$ (CIS) is known to be a very prominent absorber layer for high efficiency thin film solar cells. Current interest in the photovoltaic industry is to identify and develop more suitable materials and processes for the fabrication of efficient and cost-effective solar cells. Various processes have been being tried for making a low cost CIS absorber layer, this study obtained the CIS nanoparticles using commercial powder of 6 mm pieces for low cost CIS absorber layer by high frequency ball milling and cryogenic milling. And the CIS absorber layer was prepared by paste coating using milled-CIS nanoparticles in glove box under inert atmosphere. The chalcopyrite $CuInSe_2$ thin films were successfully made after selenization at the substrate temperature of $550^{\circ}C$ in 30 min, CIS solar cell of Al/ZnO/CdS/CIS/Mo structure prepared under various deposition process such as evaporation, sputtering and chemical vapor deposition respectively. Finally, we achieved CIS nanoparticles solar cell of electric efficient 1.74 % of Voc 29 mV, Jsc 35 $mA/cm^2$ FF 17.2 %. The CIS nanoparticles-based absorber layers were characterized by using EDS, XRD and HRSEM.

• Journal of Powder Materials
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• v.25 no.4
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• pp.291-295
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• 2018

A conductive additive is prepared by dispersing multi-walled carbon nanotubes (MWCNTs) on Cu powder by mechanical milling and is distributed in epoxy to enhance its electrical conductivity. During milling, the MWCNTs are dispersed and partially embedded on the surface of the Cu powder to provide electrically conductive pathways within the epoxy-based composite. The degree of dispersion of the MWCNTs is controlled by varying the milling medium and the milling time. The MWCNTs are found to be more homogeneously dispersed when solvents (particularly, non-polar solvent, i.e., NMP) are used. MWCNTs gradually disperse on the surface of Cu powder because of the plastic deformation of the ductile Cu powder. However, long-time milling is found to destroy the molecular structure of MWCNTs, instead of effectively dispersing the MWCNTs more uniformly. Thus, the epoxy composite film fabricated in this study exhibits a higher electrical conductivity than 1.1 S/cm.

• Transactions of the Korean hydrogen and new energy society
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• v.15 no.2
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• pp.98-107
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• 2004

Modified Ni/YSZ cermets for high temperature electrolysis were synthesized by dry or wet mechanical alloying methods. The Ni/YSZ composit particle was directly fabricated from the ball milling of Ni and YSZ powder or obtained from the reduction of NiO/YSZ particle after the ball milling of NiO and YSZ. In the case of the NiO/YSZ composite particle, the dry milling increased the average particle size whereas the wet milling decreased the size. The dry milling showed that fine YSZ particles were distributed over large Ni surfaces while Ni and YSZ particles similar in size were well mixed in the wet milling method. These features were the same in the Ni/YSZ composite particle prepared from Ni and YSZ powders. The electrical conductivity of the wet-milled Ni/YSZ cermet showed the highest value of $2{\times}10^2S/cm$ among the specimens and this value was increased to $1.4\times10^4S/cm$ after the sintering at $900^\circ{C}$ for 1 h.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.10a
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• pp.318-321
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• 2005

FIB (Focused ion Beam) milling on a 500-nm-thick silicon nitride membrane was studied in order to fabricate a high-resolution shadow mask, or called a nanostencil. The silicon nitride membrane was fabricated by MEMS processes of LPCVD, photolithography, ICP etching and bulk silicon etching. The apertures made by FIB milling and normal photolithography were compared. The square metal pattern deposited through FIB milled shadow mask showed 6 times smaller comer radius than the case of photolithography. The results show high resolution patterning could be achieved by local deposition through FIB milled shadow-mask.

• Journal of Powder Materials
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• v.19 no.3
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• pp.182-188
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• 2012

In this study, fine cathode materials $Ni_3S_2$ and $NiS_2$ were synthesized using the simple, convenient process of mechanical alloying (MA). In order to improve the cell properties, wet milling processes were conducted using low-energy ball milling to decrease the mean particle size of both materials. The cells of Na/$Ni_3S_2$ and Na/$NiS_2$ show a high initial discharge capacity of 425 mAh/g and 577 mAh/g respectively using wet milled powder particles, which is much larger than commercial ones, providing some potential as new cathode materials for rechargeable sodium-ion batteries.