• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2005.05a
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• pp.215-218
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• 2005

For the production of cold forged parts with near-net-shape attributes, the quality of the tool system is responsible for an essential portion of costs fer the finished components. Therefore, a tool lift is one of the important issues on cold forging industry. There are many complicated variables related with tool life, such as material, heat-treatment, coating, lubricant, process design. In this study, heat-treatment of tool material and lubricant are investigated to improve the tool life. Deep cryogenic treatment of tool steel is very efficient to improve the wear resistance due to the fine carbide. And, friction factor of lubricants for cold forging are measured by the ring compression test. Zinc-Phosphate and $MoS_2$ lubricant is effective to sustain the friction factor under 0.1.

• Bulletin of the Korean Chemical Society
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• v.32 no.2
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• pp.536-540
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• 2011

This study reports the origin of the electrochemical improvement of $LiFePO_4$ when synthesized by wet milling using acetone without conventional carbon coating. The wet milled $LiFePO_4$ delivers 149 $mAhg^{-1}$ at 0.1 C, which is comparable to carbon coated $LiFePO_4$ and approximately 74% higher than that of dry milled $LiFePO_4$, suggesting that the wet milling process can increase the capacity in addition to conventional carbon coating methods. UV spectroscopy, elemental microanalysis, and evolved gas analysis are used to find the root cause of the capacity improvement during the mechanochemical reaction in acetone. The analytical results show that the improvement is attributed to the conductive residual carbon on the surface of the wet milled $LiFePO_4$ particles, which is produced by the reaction of $FeC_2O_4{\cdot}2H_2O$ with acetone during wet milling through oxygen deficiency in the precursor.

• Bulletin of the Korean Chemical Society
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• v.32 no.3
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• pp.836-840
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• 2011

This study examines the effects of a carbon coating on the electrochemical performances of $LiFePO_4$. The results show that the capacity of bare $LiFePO_4$ decreased sharply, whereas the $LiFePO_4$/C shows a well maintained initial capacity. The Li ion diffusivity of the bare and carbon coated $LiFePO_4$ is calculated using cyclic voltammetry (CV) to determine the correlation between the electrochemical performance of $LiFePO_4$ and Li diffusion. The diffusion constants for $LiFePO_4$ and $LiFePO_4$/C measured from CV are $6.56{\times}10^{-16}$ and $2.48{\times}10^{-15}\;cm^2\;s^{-1}$, respectively, indicating considerable increases in diffusivity after modifications. The Li ion diffusivity (DLi) values as a function of the lithium content in the cathode are estimated by electrochemical impedance spectroscopy (EIS). The effects of the carbon coating as well as the mechanisms for the improved electrochemical performances after modification are discussed based on the diffusivity data.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2006.10a
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• pp.377-378
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• 2006

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2014.11a
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• pp.44-44
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• 2014

Magnesium alloy AZ31 sheet를 자동차용 부품으로 사용하기 위해서는 내식성, 전착도장성등의 신뢰성을 확보해야 한다. 이를 위해서 우리는 Phosphate, manganese, silicon계열의 화성처리제를 이용하여 자동차 부품으로 사용가능한 신뢰성확보를 위해 표면처리 방법에 관한 연구를 진행 하였다.

• Journal of the Korean institute of surface engineering
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• v.33 no.5
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• pp.381-386
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• 2000

It was found that colloidal silica sprayed to the galvanized steel sheet apparently made the molten zinc layer solidified to be the randomly oriented fine grains. Its spraying effect was also little affected by steel temperature that had been considered as one of the major operating factors in this process. From the results of surface analysis, it is considered that aluminum dissolved in coating layer reduces silica to silicon by the oxidation-reduction reaction, and that the reduced silicon acts as a more effective nucleus in solidification reaction than phosphate salt, siica and alumina.

• Applied Chemistry for Engineering
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• v.19 no.1
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• pp.66-72
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• 2008

Manganese hydrogen phosphate hydrate, $MnHPO_4{\cdot}2.25H_2O$, is a major constituent of the pre-conditioning compositions for the manganese phosphate coating treatment over carbon steel substrate. This compound is conventionally produced by the synthesis in the aqueous solution process followed by the filtration and drying processes and a series of size reduction and classification processes in dry state. However, it is evident that the conventional process is neither environment-friendly nor cost-effective. In this work, a new process principle was examined based on the controlled double-jet precipitation technology to produce the manganese chemical product of fairly uniform particle size distribution in an aqueous solution media. The effects of stabilizing agents were comparatively studied by the scanning electron microscope analysis in a uniformity point of view of the resulting particle size. Polyvinylpyrrolidone and Gum Arabic were excellent in controlling the crystal growth step, resulting in fairly uniform size distributions of the particles from the controlled double-jet process.

• Animal cells and systems
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• v.13 no.4
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• pp.363-370
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• 2009

Since vitamin $D_3$ is an important regulator of osteoblastic differentiation, a presently-established vitamin $D_3$-entrapped calcium phosphate film (VCPF) was evaluated for hard tissue engineering. The entrapped vitamin $D_3$ more rapidly induced bone nodule formation. To characterize the cellular events leading to regulations including faster differentiation, signal transduction pathways were investigated in osteoblastic MG63 cells at a molecular level. Major signaling pathways for MG63 cell proliferation including phosphatidylinositol-3-kinase, extracellular signal-regulated kinase, c-Jun N-terminal kinase and focal adhesion kinase pathways were markedly down-regulated when cells were cultured on calcium phosphate film (CPF) and VCPF. This agreed with our earlier observations of the immediate delay in proliferation of MG63 cells upon culture on CPF and VCPF. On the other hand, the p38 mitogen-activated protein kinase (p38 MAPK) and protein kinase A (PKA) pathways were significantly up-regulated on both CPF and VCPF. CPF alone could simulate differential behaviors of MG63 cells even in the absence of osteogenic stimulation and entrapment of vitamin $D_3$ within CPF further amplified the signal pathways, resulting in continued promotion of MG63 cell differentiation. Interplay of p38 MAPK and PKA signaling pathways likely is a significant event for the promotion of differentiation and mineralization of MG63 cells.

• Korean Journal of Materials Research
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• v.12 no.7
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• pp.560-567
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• 2002

Titanium (Ti) is a bioinert material and has lower elastic coefficient and better strength/volume property than other metals. Ferroelectric materials show alignment of positive and negative charges by poling treatment. This study was purposed to develop a new implant system by combining the advantages of Ti and ferroelectric property of $BaTiO_3$ (BTO). It was performed with the assumption that the $Ca^{2+ }$ ions would be easily attracted on negatively charged surface and the attracted cation might behave as nuclei for bone-like crystal growth in biological solutions. A ferroelectric BTO thin film on Ti was fabricated and the effect of poling treatment on the improvement of calcium phosphate (Ca-P) formation in biological solutions was evaluated. After immersion in Eagle’s minimum essential media (MEM) solution, NaCl was formed on Ti, and Ca-P layer containing NaCl was formed on Ti-O. Weak and sparse Ca-P layers were formed on BTO, while thick, homogeneous, and dense Ca-P layer was formed on negatively polarized BTO (N-BTO), which was confirmed by FE-SEM and EDX. In summary, these results demonstrate that poling the ferroelectric BTO surface negatively is effective for the formation of Ca-P layer in MEM solution, and that N-BTO coating on Ti could be used as a possible alternative method for enhancing the osseointegration of the implants.

• Journal of the Korean Ceramic Society
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• v.45 no.10
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• pp.579-583
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• 2008

A porous $Al_2O_3$, scaffold coated with tricalcium phosphate(TCP) was fabricated by replica method using polyurethane(PU) foam as a fugitive material. Successive coatings of $Al_2O_3$ and hydroxyapatite(HAp) were applied via dip coating onto polyurethane foam, which has a slender and well interconnected network. A porous structure was obtained after sequentially burning out the foam and then sintering at $1500^{\circ}C$. The HAp phase was changed to TCP phase at high temperature. The scaffold showed excellent interconnected porosity with pore sizes ranging from $300{\sim}700{\mu}m$ in diameter. The inherent well interconnected structural feature of PU foam remained intact in the fabricated porous scaffold, where the PU foam material was entirely replaced by $Al_2O_3$ and TCP through a consecutive layering process. Thickness of the $Al_2O_3$ base and the TCP coating was about $7{\sim}10{\mu}m$ each. The TCP coating was homogeneously dispersed on the surface of the $Al_2O_3$ scaffold.