• Transactions of the Korean hydrogen and new energy society
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• v.25 no.4
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• pp.436-442
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• 2014

$LaCoO_3$ powders synthesized by Pechini process were pulverized by planetary ball-milling to decrease particle size and characterized as a catalyst in alkaline solution for oxygen reduction and evolution reaction (ORR & OER). The changes of physical properties, such as particle size distribution, surface area and electric conductivity, were analyzed as a function of ball-milling time. Also, the variations of the crystal structure and surface morphology of ball-milled powders were examined by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. The electrochemically catalytic activities of the intrinsic $LaCoO_3$ powders decreased with increasing ball-milling time, but their electrochemical performance as an electrode improved by the increase of the surface area of the powder.

• Journal of the Korean Physical Society
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• v.73 no.9
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• pp.1340-1345
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• 2018

Mo-10 at.% Cu nanocomposite powders were fabricated by using planetary ball-milling (PBM), a mechanical alloying technique for preparing nanocomposite alloy powders of metals with mutual insolubility, and the variations in the physical and the chemical characteristics with the process conditions were investigated. We observed that Mo-10 at.% Cu was an appropriate composition to ensure a good alloying grade and minimal welding between particles. The influences of the temperature and the milling conditions on the mechanical alloying process and the phase change of Mo-10 at.% Cu composite powders were investigated, and the particle and the grain sizes of the powders after mechanical alloying were confirmed. The Mo-10 at.% Cu powders showed homogeneous elemental distributions and no phase changes up to $1200^{\circ}C$; their compositions were retained after the mechanical alloying process. The finest grain size obtained was about 5 nm for powders processed using optimum PBM processing conditions: ball-to-powder weight ratio of 5 : 1, ambient air atmosphere, a milling time of 20 h, a rotation speed of 200 rpm, and a stearic acid content of 4 wt.% produced superfine-grained Mo-10 at.% Cu nanocomposite powders with an average grain size of 5 nm (which is smaller than that of other similar materials reported in the literature). The analytical results confirmed that the PBM technique presented here is a promising method for preparing superfine-grained Mo-10 at.% Cu powders with improved properties.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1999.06a
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• pp.119-126
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• 1999

The rolling fatigue lives (RFL) of five kinds of silicon nitride balls were investigated. Four kinds of Si$_3$N$_4$ balls were fabricated using different raw materials, sintering aids and sintering conditions, Commercially available Si3N4 ball was also studied for comparison. All the balls were finished up to the dimensional accuracy of Grade 10 defined in KS B 2001 (Steel Balls for Ball Bearings) with a size of 9.525mm. RFL tests were then conducted under the initial theoretical maximum contact stress 6.38 GPa and the spindle speed 10,000 rpm. Gear oil was provided by oiled race as lubricant. The results of RFL test indicated the prerequisitic conditions for the long rolling life of Si$_3$N$_4$ball : (1) the high density, (2) mjcrostructures consisted of small uniformly distributed grains, (3) little glassy phase in grainboundary, and (4) little crystalline phase and secondary phase that induces residual thermal stress due to the differences of thermal expansion coefficient with Si$_3$N$_4$Phase.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.2 s.173
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• pp.319-328
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• 2000

This paper presents a new design method of the 1 generation wheel bearing unit using a numerical optimization technique in order to increase bearing fatigue life. For calculating the fatigue life, a method of load analysis is studied on the automotive wheel bearing system. The design variables selected are ball size, initial contact angle, number of balls, pitch diameter, pre-load, and distance between ball centers. The method of feasible directions in ADS (Automated Design Synthesis) is utilized to automatically find the optimum design variables. To validate the design method, a computer program is developed and applied to a practical passenger car model. The optimum design results demonstrated the effectiveness of the proposed design method showing that the system life of the optimally designed wheel bearing unit is enhanced in comparison with that of the initial ones within the given available design space.

• Journal of the Korean Society of Safety
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• v.25 no.3
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• pp.1-6
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• 2010

Ball bearings are one of main components that support the rotational shaft in high speed rotary machinery. So, it is very important to detect the incipient faults and fault growth of bearing since the damage and failure of bearing can cause a critical failures or accidents of machinery system. In the past, many researchers mainly performed to detect the bearing fault using traditional method such as wavelet, statistics, envelope etc in vibration signals. But study on the detection technique for bearing fault growth has a little been performed. In this paper, we verified the possibility for monitoring of fault growth and detection of fault size in bearing outer-race by using the envelope powerspectrum and probabilistic density function from measured vibration signals.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.07a
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• pp.705-708
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• 2001

The effect of grinding on the synthesis of LaAO$_3$ceramics was investigated. The mixture ground by plantary ball mill showed 70nm particle size (wet ball mill or unground=0.5 $\mu$m). Monophase LaAlO$_3$powders were formed when ground samples were heated at 100$0^{\circ}C$, however unground samples required temperatures above 130$0^{\circ}C$. Density of the ground samples sintered at 140$0^{\circ}C$ showed 98.3% of theoretical density (unground=93.5% at 150$0^{\circ}C$). Dielectric constant of the ground samples($\varepsilon$r=22.4) showed higher values than that of the unground samples($\varepsilon$r=20.32). Temperature coefficient of capacitance($\tau$$_{c}$) and dielectric loss (tan$\delta$) of the ground samples were similar to those of unground samples.s.

• Tribology and Lubricants
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• v.15 no.2
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• pp.150-155
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• 1999

The rolling fatigue lives (RFL) of five kinds of silicon nitride balls were investigated. Four kinds of Si$_3$N$_4$balls were fabricated using different raw materials, sintering aids and sintering conditions. Commercially available Si$_3$N$_4$ball was also studied for comparison. All the balls were finished up to the dimensional accuracy of Grade 10 defined in KS B 2001 (Steel Balls fer Ball Bearings) with a size of 9.525 mm. RFL tests were then conducted under the initial theoretical maximum contact stress 6.38 GPa and the spindle speed 10,000 rpm. Gear oil was provided by oiled race as lubricant. The results of RFL test indicated the prerequisitic conditions for the long rolling life of Si$_3$N$_4$ball : (1) the high density, (2) microstructures consisted of small uniformly distributed grains, (3) little glassy phase in grainboundary, and (4) little crystalline phase and secondary phase that induces residual thermal stress due to the differences of thermal expansion coefficient with Si$_3$N$_4$phase.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.1264-1265
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• 2006

Study about the feasibility and effect of high-energy ball milling on a specific Mg alloy under protection medium of alcohol was presented via comparing with conventional vacuum milling. More fine particles with wider powder size distribution but more irregular shape were shown of the powder milled under alcohol. No obvious oxide was revealed from the two kinds of Mg alloy powders with limited milling time. And since slip induced in a preferential direction, the (002) texture was formed in the Mg alloy powders at the initial stage of alcohol milling. More O and Fe contaminants were introduced into the powders milled under alcohol according to the EDS analysis.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2008.05a
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• pp.473-476
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• 2008

In this paper, we designed the main mechanism of high throughput device for rod-cuts of spent fuel. For this, we analyzed the mechanical methods(slitting, ball mill, roller straightening) and chemical methods(muffle furnace, rotary kiln). As the results, methods of ball drop and rotary drum for concepts design were selected in the analysis step. For enhancement of oxidation rate, we devised the blades on the reactor with mesh type. Also, for enhancement of decladding rate, we designed ball size and rotation reactor with mesh type and devised the vacuum system for fission products. Mechanisms of oxidation and recovery can simultaneously handle the rod-cuts of spent fuel and independently recover. The results of mechanism design can be used for scale-up of high throughput device.

• Journal of KSNVE
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• v.9 no.2
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• pp.387-392
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• 1999

This paper presents design guidelines for the automatic ball balancer in CD/DVD systems with varying eccentricity. In these systems, the size of balancing balls should be limited by the restricted race space so that determination of the number and mass of balls should consider the radii of the race and the balls. In addition, the effects of viscosity and friction also should be taken into account for sufficient balancing. Based on the static equilibrium conditions, the number and mass of balls corresponding to the range of varying eccentricity have been determined. Dynamic simulation with viscosity and friction shows sufficient viscosity must exist to ensure stability and friction between balls and race must be minimized to guarantee accurate balancing.