• Journal of Electrical Engineering and Technology
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• v.12 no.6
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• pp.2256-2261
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• 2017

Carbon nanotube (CNT) and alumina ($Al_2O_3$) are synthesized into hybrid composites, and an advanced electrical discharge machining (EDM) system is developed for the machining of hard and conductive materials. CNT nanoparticles are mixed with $Al_2O_3$ powder and the $Al_2O_3$/CNT slurry is sintered by spark plasma. The hardness and the electrical conductivity of the $Al_2O_3$/CNT hybrid composite were investigated. The electrical discharge is controlled by a capacitive ballast circuit. The capacitive ballast circuit is applied to the tungsten carbide and the $Al_2O_3$/CNT hybrid composite. The voltage-current waveforms and scanning electron microscope (SEM) images were measured to analyze the characteristics of the boring process. The developed EDM process can manufacture the ceramic based hybrid composites, thereby expecting the variety of applications.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.27 no.12
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• pp.2085-2091
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• 2003

An ultrasonic machining process has been known as efficient and economical means fer precision machining of glass or ceramic materials. However, because of its complexity, the mechanism of the machining process is still not well understood. Therefore, it is hard to optimize the process parameters effectively. The conventional ultrasonic machining which uses the abrasive slurry only, furthermore, is time-consuming and gives the relatively rough surface. In order to increase the material removal rate and improve the integrity of the machined surface, we have introduced the novel ultrasonic machining technique, Chemical-assisted UltraSonic Machining(CUSM). The desktop-style micro ultrasonic machine has been developed and the z-axis feed is controlled by the constant load control algorithm. To obtain the chemical effects, the low concentration HF(hydrofluoric acid) solution, which erodes glass, added to alumina slurry. Through various experiments and comparison with conventional results, the superiority of CUSM is verified. MRR increases over 200%, the surface roughness is improved and the machining load decreases dramatically.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.13 no.6
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• pp.119-126
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• 2014

Micro-holes of conductive ceramic are required in micro structures. Micro-electrical discharge machining (Micro-EDM) is an effective machining method since EDM is as process for shaping hard metals and complex-shaped holes by spark erosion in all kinds of electro-conductive materials. However, as the depth of micro hole increases, the machining condition becomes more unstable due to inefficient removal of debris between the electrode and the workpiece. In this paper, micro-EDM was performed to evaluate machining characteristic such as electrode wear, machining time, taper angle, radial clearance with varying voltage and ultrasonic vibration on 10 vol.% Carbon-nanotube reinforced conductive $Al_2O_3$ composite fabricated by spark plasma sintering in previous research.

• Transactions of the Korean Society of Automotive Engineers
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• v.1 no.2
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• pp.103-116
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• 1993

Recently, engineering ceramics called as the 3 material have been concerned significantly with some excellent mechanical properties and many functions as new materials for high precision mechanical components and engineering parts for at large. Then, for designing engineering parts using engineering ceramics, bending strength value data with high reliability is more essential than any other mechanical properties. But, because of brittleness and structural characteristic, it is very hard to grind with conventional tools, and the generation of cracks and various defects of engineering ceramics parts during grinding machining process are serious problems. Thus, in present study, surface grinding experiments with various machining conditions using resin bond diamond wheels are carried out to obtain the most excellent guality of testpiece surface and optimum step of grinding process for the high efficient stock removal rate to save running time. As the results from grinding experiments and 3-points bending strength test of ground Al2O3 ceramics parts on Korean Standard, manufactured in our country and Japan, basic technology and know-how to develop the optimum grinding machining conditions and also high bending strength values with high reliability are obtained.

• Bulletin of the Korean Chemical Society
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• v.31 no.4
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• pp.976-980
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• 2010

A series of arylacetylene resins with siloxane units were synthesized by the condensation reactions of m-diethynylbenzene magnesium reagents with various $\alpha,\omega$-bis(chloro)dimethylsiloxanes. These resins are liquids and are miscible with common organic solvents at room temperature. The structures of the resins were characterized by FT-IR, $^1H$ NMR, $^{13}C$ NMR, $^{29}Si$ NMR, and gel permeation chromatography (GPC). The thermal behaviors of the resins were examined with differential scanning calorimetry (DSC). These resins have good processability. They can be thermally cross-linked through the ethynyl groups to produce cured resins. The thermal and thermooxidative stabilities of the cured resins were studied by thermogravimetric analysis (TGA). The cured resins possess high thermal and thermooxidative stability. Their decomposition occurs at above $500^{\circ}C$ in both $N_2$ and air. With increasing the length of siloxane units in the resins, the thermal stability of the cured resins decreases in $N_2$. When the cured resins were sintered above $1450^{\circ}C$ under argon, hard and glassy SiOC ceramics were obtained. These SiOC ceramics have the decomposition temperatures at 5% weight loss above $800^{\circ}C$ in air.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2017.05a
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• pp.79-79
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• 2017

Metallic biomaterials have been mainly used for the fabrication of medical devices for the replacement of hard tissue such as artificial hip joints, bone plates, and dental implants. Because they are very reliable on the viewpoint of mechanical performance. This trend is expected to continue. Especially, Ti and Ti alloys are bioinert. So, they do not chemically bond to the bone, whereas they physically bond with bone tissue. For their poor surface biocompatibility, the surface of Ti alloys has to be modified to improve the surface osteoinductivity. Recently, ceramic-like coatings on titanium, produced by plasma electrolytic oxidation (PEO), have been developed with calciumand phosphorus-enriched surfaces. A lso included the influences of coatings, which can accelerate healing and cell integration, as well as improve tribological properties. However, the adhesions of these coatings to the Ti surface need to be improved for clinical use. Particularly Silicon (Si) has been found to be essential for normal bone, cartilage growth and development. This hydroxyapatite, modified with the inclusion of small concentrations of silicon has been demonstrating to improve the osteoblast proliferation and the bone extracellular matrix production. Strontium-containing hydroxyapatite (Sr-HA) was designed as a filling material to improve the biocompatibility of bone cement. In vitro, the presence of strontium in the coating enhances osteoblast activity and differentiation, whereas it inhibits osteoclast production and proliferation. The objective of this work was to study Morphology of bone-like apatite formation on Sr and Si-doped hydroxyapatite surface of Ti-6Al-4V alloy after plasma electrolytic oxidation. Anodized alloys was prepared at 270V~300V voltages with various concentrations of Si and Sr ions. Bone-like apatite formation was carried out in SBF solution. The morphology of PEO, phase and composition of oxide surface of Ti-6Al-4V alloys were examined by FE-SEM, EDS, and XRD.

• Korean Journal of Materials Research
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• v.30 no.7
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• pp.343-349
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• 2020

NKN [(Na,K)NbO₃] is a candidate lead-free piezoelectric material to replace PZT [Pb(Zr,Ti)O₃]. A single crystal has excellent piezoelectric-properties and its properties are dependent of the crystal orientation direction. However, it is hard to fabricate a single crystal with stoichiometrically stable composition due to volatilization of sodium during the growth process. To solve this problem, a solid solution composition is designed (Na,K)NbO₃-Ba(Cu,Nb)O₃ and solid state grain growth is studied for a sizable single crystal. Ceramic powders of (Na,K)NbO₃-M(Cu,Nb)O₃ (M = Ca, Sr, Ba) are synthesized and grain growth behavior is investigated for different temperatures and times. Average normal grain sizes of individual specimens, which are heat-treated at 1,125 ℃ for 10 h, are 6.9, 2.8, and 1.6 ㎛ for M = Ca, Sr, and Ba, respectively. Depending on M, the distortion of NKN structure can be altered. XRD results show that (NKN-CaCuN: shrunken orthorhombic; NKN-SrCuN: orthorhombic; NKN-BaCuN: cubic). For the sample heat-treated at 1,125 ℃ for 10 h, the maximum grain sizes of individual specimens are measured as 40, 5, and 4,000 ㎛ for M = Ca, Sr, and Ba, respectively. This abnormal grain size is related to the partial melting temperature (NKN-CaCuN: 960 ℃; NKN-SrCuN: 971 ℃; NKN-BaCuN: 945 ℃).

• Journal of Periodontal and Implant Science
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• v.33 no.1
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• pp.13-26
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• 2003

Periodontal regeneration therapy with bone-substituting materials has gained favorable clinical efficacy by enhancing osseous regeneration in periodontal bony defect. As bone-substituting materials, bone powder, calcium phosphate ceramic, modified forms of hydroxyapatite, and hard tissue replacement polymer have demonstrated their periodontal bony regenerative potency. Bone-substituting materials should fulfill several requirements such as biocompatibility, osteogenecity, malleability, biodegradability. The purpose of this study was to investigate biocompatibility, osteo-conduction capacity and biodegradability of $Na_2O$, $K_2O$ added calcium metaphosphate(CMP). Beta CMP was obtained by thermal treatment of anhydrous $Ca_2(H_2PO_4)_2$. $Na_2O$ and $K_2O$ were added to CMP. The change of weight of pure CMP, $Na_2O$-CMP, and $K_2O$-CMP in Tris-buffer solution and simulated body fluid for 30 days was measured. Twenty four Newzealand white rabbits were used in negative control, positive control(Bio-Oss), pure CMP group, 5% $Na_2$-CMP group, 10% $Na_2O$-CMP goup, and 5% $K_2O$-CMP group. In each group, graft materials were placed in right and left parietal bone defects(diameter 10mm) of rabbit. The animals were sacrificed at 3 months and 6 months after implantation of the graft materials. Degree of biodegradability of $K_2O$ or $Na_2O$ added CMP was greater than that of pure CMP in experimental condition. All experimental sites were healed with no clinical evidence of inflammatory response to all CMP implants. Histologic observations revealed that all CMP grafts were very biocompatible and osseous conductive, and that in $K_2O$-CMP or $Na_2O$-CMP implanted sites, there was biodegradable pattern, and that in site of new bone formation, there was no significant difference between all CMP group and DPBB(Bio-Oss) group. From this result, it was suggested that all experimental CMP group graft materials were able to use as an available bone substitution.

• Fire Science and Engineering
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• v.33 no.3
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• pp.105-111
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• 2019

In Korea, the results of a field survey on the construction of flammable exterior materials implemented in 2018 revealed that 147,559 buildings belong to this category. It was found that the fire spreading cases in upper and adjacent constructions are about 3,500 per year, the fires of starting in flammable exterior material are about 1,500 per year. In this study, we investigated the repair method of buildings constructed by flammable exterior material and conducted performance verification of each repair materials for prevention of similar fire. In the case of the repair method, a method of reinforcing with a repair material after removing the existing building finishing material and a method of attaching the repair material after performing the face finishing are proposed. In addition, we conducted cone calorimeter tests of 6 materials such as fireproof gypsum board, mineral wool, hard urethane foam, ceramic board and ALC panel as dryvit and repairing materials, and investigated basic combustion performance of that materials.

• Journal of Adhesion and Interface
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• v.13 no.4
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• pp.171-181
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• 2012

The demand characteristics of the conventional 12 kinds of epoxy resins which have been used for restoration of the ceramic relics were investigated to provide standards of the effective materials in this study. The result of durability analysis showed that a liquid type is more effective in ceramic relics (low damage, high strength), and a paste type is more effective in earthenware relics (high damage, low strength). The result of workability analysis appears that the liquid type is higher than the paste type, and a slow curing type is higher than a fast curing type in surface hardness. Therefore, in the case of the liquid type which is hard to reprocess due to high surface hardness, it is necessary to conduct a study on improving physical properties by adding filler. The result of the gloss analysis on epoxy resins showed that the liquid type (colorless) has higher gloss than the paste type, and the slow curing type has higher gloss than the fast curing type in liquid types. CDK-520A/520B and Araldite SV 427-2/HV 427-1 showed the most similar gloss to $700^{\circ}C$ earthenware, Devcon 5 minute, EPO-TEK 301-2, and Quik Wood showed the most similar gloss to celadon and whiteware, Quik Wood, EPO-TEK 301-2, and Devcon 5 minute showed the most similar gloss to buncheongware. It is necessary for conservator to decide the range of the restoration surface by predicting the increase and decrease of the restoration surface because most of the epoxy resins caused the volume change in curing process.