• Journal of Technologic Dentistry
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• v.42 no.4
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• pp.307-312
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• 2020

Application of ceramic materials for fabrication of dental restoration materials has been a focus of interest in the field of esthetic dentistry. The ceramic materials of choice are glass ceramics, spinel, alumina, and zirconia. The development of yttrium tetragonal zirconia polycrystal (YTZP)-based systems is a recent addition to all-ceramic systems that have high strength and are used for crowns and fixed partial dentures. Computer-aided design/computer-aided manufacturing (CAD/CAM)-produced, YTZP-based systems are popular with respect to their esthetic appeal for use in stress-bearing regions. The highly esthetic nature of zirconia and its superior physical properties and biocompatibility have enabled the development of restorative systems that meet the demands of today's patients. Many in vitro trials have been performed on the use of zirconia; however, relatively fewer long-term clinical studies have been published on this subject. The use of zirconia frameworks for long-span fixed partial dentures is currently being evaluated; in the future, more in vivo research and long-term clinical studies are required to provide scientific evidence for drawing solid guidelines. Further clinical and in vitro studies are required to obtain data regarding the long-term clinical use of zirconia-based restorations.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.16 no.6
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• pp.1-6
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• 2017

Recently, the brittle materials such as ceramics, glass, sapphire and textile material have been widely used in semiconductors, aerospace and automobile owing to high functional characteristics. On the other hand, it has the characteristics of difficult-to-cut material relative to all materials. In this study, diamond electro-deposited band-saw machine was developed to operate stably using water-coolant type through relative motion between band-saw tool and $Al_2O_3$ material. High densified $Al_2O_3$ material was manufactured by spark plasma sintering method. The bulk density was observed by the Archimedes law and the theoretical density was estimated to be $3.88g/cm^3$ and its hardness 14.7 MPa. From the dicing sawing test of $Al_2O_3$ specimen, behavior of surface roughness and band-saw wear are dominantly affected by the increase of the band-saw linear velocity. Additionally, an continuous pattern type of diamond band-saw was a very effective due to entry impact as a one-off for brittle material.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.28 no.6
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• pp.235-242
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• 2018

High temperature electrical conductivity of Aluminum Nitride (AlN) ceramics sintered with $Y_2O_3$ as a sintering aid has been investigated with respect to various sintering conditions and MgO-dopant. When magnesium oxide is added as a dopant, liquid glass-film and crystalline phases such as spinel, perovskite are formed as second phases, which affects their electrical properties. According to high temperature impedance analysis, MgO doping leads to reduction of activation energy and electrical resistivity due to AlN grains. On the other hand, the activation energy and electrical resistivity due to grain boundary were increased by MgO doping. This is a result of the formation of liquid glass film in the grain boundary, which contains Mg ions, or the elevation of schottky barrier due to the precipitation of Mg in the grain boundary. For the annealed sample of MgO doped AlN, the electrical resistivity and activation energy were increased further compared to MgO doped AlN, which results from diffusion of Mg in the grains from grain boundary as shown in the microstructure.

• Journal of the Korean Ceramic Society
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• v.42 no.8 s.279
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• pp.554-560
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• 2005

The engineering ceramic needs the properties of high strength, hardness, corrosion-resistance and heat-resistance in order to withstand thermal shock or applied nonuniform stresses without failure. The densely coated porous ceramics can be used for machine component, electromagnetic component, bio-system component and energy-system component by their high-performances from superior coating properties and light-weight characteristics due to the structure including pore by itself. In this study we controlled the porosity of silica and alumina, $8.2\~25.4\%$ and $23.4\~36.0\%$, respectively, by the control of sintering temperature and starting powder size. We made bilayer structures, consisting of a transparent glass coating layer bonded to a thick substrate of different porous ceramics by a thin layer of epoxy adhesive, facilitated observations of crack initiation and propagation. The elastic modulus mismatch could be controlled using different porous ceramics as the substrate layer. Then we applied 150 N force using WC sphere with a radius of 3.18 mm by Hertzian indentation. As a result, the crack initiation in the coating layer was delayed at lower porosity in the substrate layer, and the damage in the coating layer was relatively smaller at the bilayer structure coated on higher elastic substrate.

• Journal of the Microelectronics and Packaging Society
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• v.25 no.4
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• pp.95-99
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• 2018

High thermal conductivity films with electrically insulating properties have a great potential for the effective heat transfer as substrate and thermal interface materials in high density and high power electronic packages. There have been lots of studies to achieve high thermal conductivity composites using high thermal conductivity fillers such alumina, aluminum nitride, boron nitride, CNT and graphene, recently. Among them, hexagonal-boron nitride (h-BN) nano-sheet is a promising candidate for high thermal conductivity with electrically insulating filler material. This work presents an enhanced heat transfer properties of ceramic/polymer composite films using h-BN nano-sheets and PVA polymer resins. The h-BN nano-sheets were prepared by a mechanical exfoliation of h-BN flakes using organic media and subsequent ultrasonic treatment. High thermal conductivities over $2.8W/m{\cdot}K$ for transverse and $10W/m{\cdot}K$ for in-plane direction of the cast films were achieved for casted h-BN/PVA composite films. Further improvement of thermal conductivity up to $13.5W/m{\cdot}K$ at in-plane mode was achieved by applying uniaxial compression at the temperature above glass transition of PVA to enhance the alignment of the h-BN nano-sheets.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.24 no.4
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• pp.297-302
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• 2011

Recently, low temperature co-fired ceramic (LTCC) technology is widely used in sensors, actuators and microsystems fields because of its very good electrical and mechanical properties, high reliability and stability as well as possibility of making 3D micro structures. In this study, we investigated the effects of sputtering gas ratio and annealing temperature on the crystal structure of $Pb(ZrTi)O_3$ (PZT) thin films deposited on LTCC substrate. The LTCC substrate with thickness of $400\;{\mu}m$ were fabricated by laminating 4 green tapes which consist of alumina and glass particle in an organic binder. The PZT thin films were deposited on Pt / Ti / LTCC substrates by RF magnetron sputtering method. The results showed that the crystallization of the films were enhanced as increasing $O_2$ mixing ratio. At about 25% $O_2$ mixing ratio, was well crystallized in the perovskite structure. PZT thin films was annealed at various temperatures. When the annealing temperature is lower, the PZT thin films become a phyrochlore phase. However, when the annealing temperature is higher than $600^{\circ}C$, the PZT thin films become a perovskite phase. At the annealing temperature of $700^{\circ}C$, perovskite PZT thin films with good quality structure was obtained.

• The Journal of Korean Academy of Prosthodontics
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• v.38 no.2
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• pp.129-146
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• 2000

An increasing demand for esthetic restorations has led to the development of new ceramic systems. In-Ceram, a glass-infiltrated alumina ceramic has three to few times greater flexural strength than other ceramic glass material. Because of its high strength, In-Ceram has been suggested as inlay, crown, laminate veneer and core material for resin bonded fixed partial dentures. This clinical application requires a stable resin bond to In-Ceram core. The purpose of this study was to evaluate the shear bond strength between In-Ceram core and resin cements according to various surface treatments and storage conditions. The surface of each In-Ceram core sample was subjected to one of the following treatments and then bonded to Panavia 21 or Variolink II resin cement. ; (1) sandblasting with $110{\mu}m$ aluminum oxide powder, (2) sandblasting and silanization, (3) sandblasting and Siloc treatment, (4) sandblasting and Targis link application. Each of eight bonding groups was tested in shear bond strengths after the following storage times and thermocycling. ; A) 24 hours storage in distilled water at $37^{\circ}C$, B) 5 weeks storage in distilled water at $37^{\circ}C$ C) 5 weeks storage in distilled water at $37^{\circ}C$ and thermocycled 2,000 thormocycling for every 10 days(totally 10,000 thermocycting) in $5^{\circ}C-55^{\circ}C$ bath. The bond failure modes were observed with scanning electron microscope(SEM). The results were as fellows : 1 The shear bond strengths of sandblasting group were significantly lesser than the other groups after 24 hours water storage. No significant difference of bonding strengths was found between storage time conditions(24 hours and 5 weeks). The shear bond strengths showed a tendency to decrease in Variolink II bonding groups and to increase in Panavia 21 bonding groups. 3. After thermocycling, the shear bond strengths of all groups were significantly decreased(p<0.01) and Targis link group exhibited significantly greater strengths than the other groups(p<0.05). 4. Panavia 21 bonding groups exhibited significantly greater bonding strengths in sandblasting group(p<0.01) and silane group(p<0.05) than Variolink II bonding groups. 5. In observation of bond failure modes, Targis link group showed cohesive failure in resin part and silane group and Siloc group showed complex failure and sandblasting group showed adhesive failure between In-Ceram and resin.

• Restorative Dentistry and Endodontics
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• v.34 no.1
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• pp.69-79
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• 2009

The purpose of this study was to evaluate the influence of elastic modulus of restorative materials and the number of interfaces of post and core systems on the stress distribution of three differently restored endodontically treated maxillary second premolars using 3D FE analysis. Model 1, 2 was restored with a stainless steel or glass fiber post and direct composite resin. A PFG or a sintered alumina crown was considered. Model 3 was restored by EndoCrown. An oblique 500 N was applied on the buccal (Load A) and palatal (Load B) cusp. The von Mises stresses in the coronal and root structure of each model were analyzed using ANSYS. The elastic modulus of the definitive restorations rather than the type of post and core system was the primary factor that influenced the stress distribution of endodontically treated maxillary premolars. The stress concentration at the coronal structure could be lowered through the use of definitive restoration of high elastic modulus. The stress concentration at the root structure could be lowered through the use of definitive restoration of low elastic modulus.