• The Journal of Korean Academy of Prosthodontics
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• v.39 no.1
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• pp.14-24
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• 2001

The purpose of this study was to compare the fracture strengths and the fracture patterns of several hybrid-ceramic crowns and metal-ceramic crown. Ten crowns were constructed for each group according to the manufacturer's instruction. Removable template of silicone rubber impression material was used for standardization of each crowns. Each crown was cemented on a metal die with hybrid glass ionomer cement. All crowns cemented were stored in distilled water, $36^{\circ}C$ for 24 hours prior to loading in an universal testing machine. The load was directed at 130 degrees the long axis of metal die. The fracture strengths were measured and the fracture patterns were observed. The following results were obtained from this study 1. The mean fracture strengths of $Artglass^{(R)}$, $Sculpture^{(R)}$ and $Targis^{(R)}$ were $57.5{\pm}9.5Kgf,\;62.7{\pm}12.2Kgf$ and $60.2{\pm}10.1Kgf$ respectively. There was no significant difference among each hybrid ceramic crown group. 2. The toad required to fracture hybrid-ceramic crowns was significantly smaller than metal-ceramic crowns($131.7{\pm}22.0Kgf$). 3. In the metal-ceramic crowns, labial porcelain detached partially from porcelain-metal junction of proximal side by load. 4. Hybrid-ceramic crowns showed a simple fracture pattern that fracture line began at the loading area and extended through proximal surface, perpendicular to the margin. The crown was separated into two parts of labial side and lingual side. Above results revealed that three kinds of the hybrid-ceramic crowns used in this study must have careful application in clinical use since the strength of hybrid-ceramic crown was lower(about 1/2) than that of metal-ceramic crown.

• The Journal of Korean Academy of Prosthodontics
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• v.42 no.1
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• pp.49-57
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• 2004

Statement of problem : The increased awareness of esthetics in dentistry has brought the esthetic consideration in prosthetic restorations . Dental ceramics offer better esthetics for use of prosthetic restorations. Unfortunately, dental ceramic materials are not always the most suitable candidate materials since their inherently brittle nature. In recent years, basic research in ceramic science has led to the recognition or several approaches to strengthen and to enhance esthetics of ceramics. Several all ceramic systems use ceramic core and porcelain build up structures . Ceramic cores influence to strength of all ceramic crowns . So the strength of ceramic cores is important to all ceramic crowns. Purpose : The purpose of this study is to estimate the flexural strength of ceramic cores in some all ceramic systems. Material and method : A biaxial flexure test was conducted on three groups(Cergo, Empress 2, In-Ceram). Each group consisted of 30 discs of nearly identical dimension with a 0.5mm, 1.0mm, 1.5mm thickness and 12mm in diameter. The fracture load was recorded by Instron. Analysis of valiance(ANOVA) and Tukey's tests were performed using SAS statistical software. Results : 1.5mm thickness of specimens were significantly stronger than 0.5mm and 1.0mm thickness of specimens in Cergo and In-Ceram. But each sepecimen group of Empress 2 was no significantly strength by thickness. In order of In-Ceram, Empress 2 and Cergo has significantly stronger strength in the same thickness. Conclusion : In-Ceram is the strongest ceramic material in 3 materials. All the materials can be used according to the required characters.

• Journal of Powder Materials
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• v.27 no.6
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• pp.490-497
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• 2020

The 3D printing process provides a higher degree of freedom when designing ceramic parts than the conventional press forming process. However, the generation and growth of the microcracks induced during heat treatment is thought to be due to the occurrence of local tensile stress caused by the thermal decomposition of the binder inside the green body. In this study, an alumina columnar specimen, which is a representative ceramic material, is fabricated using the digital light process (DLP) 3D printing method. DTG analysis is performed to investigate the cause of the occurrence of microcracks by analyzing the debinding process in which microcracks are mainly generated. HDDA of epoxy acrylates, which is the main binder, rapidly debinded in the range of 200 to 500℃, and microcracks are observed because of real-time microscopic image observation. For mitigating the rapid debinding process of HDDA, other types of acrylates PETA, PUA, and MMA are added, and the effect of these additives on the debinding rate is investigated. By analyzing the DTG in the 25 to 300℃ region, it is confirmed that the PETA monomer and the PUA monomer can suppress the rapid decomposition rate of HDDA in this temperature range.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.12
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• pp.6106-6113
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• 2013

Automotive three-way catalyst substrate has a cordierite ceramic honeycomb structure. The substrate in the high engine speed range doesn't satisfy the design fatigue life due to the low mechanical properties of cordierite ceramic. SiC ceramic has higher mechanical properties than cordierite ceramic. If the automotive three-way catalyst substrate is made from the SiC ceramic honeycomb structure, the substrate can be prevented from premature failure. In this study, the mechanical properties of SiC ceramic honeycomb substrate were estimated by FEA. The FEA results indicated that the MOR and elastic modulus for the SiC ceramic honeycomb substrate was much higher than those for the cordierite ceramic honeycomb substrate.

• Journal of the Korean Ceramic Society
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• v.52 no.6
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• pp.473-478
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• 2015

Green bodies of earthenware tile were prepared from a mixture of earthenware tile powder and SiC as forming agents by applying a conventional process. Granule powder for tile samples was prepared using the spray drying method with commercial earthenware raw material with a quantity of SiC of 0.3 wt%. The applied pressure was $250kg{\cdot}f/m^2$ and the firing temperature was $1050-1200^{\circ}C$. The effects of the SiC particle size and sintering temperature on the open porosity and total porosity were investigated and the correlative mechanism was also discussed. While total porosity was not significantly changed by decreasing the SiC particle size, the open porosity showed a gradual decrease, which represents an increase of the closed porosity. As the sintering temperature increased, coarsening was made among the pores due to excessive oxidation. The volume shrinkage and bending strength were demonstrated for the sintered tile samples. The sintered bulk density was also measured to determine the weight reduction value.

• Journal of the Semiconductor & Display Technology
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• v.21 no.1
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• pp.119-126
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• 2022

MAS-based glass, which has been studied to replace the ceramic material used in the plasma etching chamber, has problems such as forming and processing due to its high melting temperature. To solve this problem, in this study, fluoride was added to the existing MAS-based glass to increase the workability in the glass manufacturing and to improve the chemical resistance to CF₄/Ar/O₂ plasma gas. Through RAMAN analysis, the structural change of the glass according to the addition of fluoride was observed. In addition, it was confirmed that high-temperature viscosity and thermal properties decreased as the fluoride content increased and plasma resistance was maintained, it showed an excellent etching rate of up to 11 times compared to quartz glass.

• Journal of the Korean Ceramic Society
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• v.52 no.6
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• pp.395-402
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• 2015

The suspension plasma spray (SPS) technique has been used to obtain dense $Y_2O_3$ coatings and to overcome the drawbacks of the conventional air plasma spray (APS). SPS uses suspensions containing micrometer or sub-micrometer sized powders dispersed in liquid media. In this study, microstructure developments and mechanical properties have been investigated as functions of particle size of source material and plasma processing parameters such as plasma power and stand-off distance. The microstructure of the coating was found to be highly related to the particle size and the plasma processing parameters, and it was directly reflected in the hardness and the adhesion strength. When fine powder (BET $16.4m^2/g$) was used as a raw material in the suspension, there was, with increasing stand-off distance, a change from a dense structure with a slightly bumpy surface to a porous structure with a cauliflower-like surface. On the other hand, when a coarse powder (BET $2.8m^2/g$) was used, the coating density was lower, with microscopic splats on the surface. Using fine $Y_2O_3$ powders, the coating layer with an optimum short stand-off distance showed a high hardness of approximately 90% of that of sintered $Y_2O_3$ and an adhesion strength several times higher than that of the coating by conventional APS.

• Journal of the Korean Ceramic Society
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• v.33 no.9
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• pp.977-984
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• 1996

This paper analyzes the performance of a rectangular dielectric ceramic antenna by the theoretical cavity model such as input impedance resonant frequency quality factor efficiency and bandwidth. Through a compu-ter simulation variation of the antenna characteristics is found as a function of the antenna parametes. (permit-tivity permeability antenna size etc) Based on the results we propose a new design method for the dielectric ceramic antenna to be employed in Global Positioning Systems.

• Proceedings of the Materials Research Society of Korea Conference
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• 1998.08a
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• pp.131.3-131
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• 1998

• Journal of Korean Society for Atmospheric Environment
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• v.19 no.3
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• pp.297-306
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• 2003

Works were focused on back pressure characteristics of ceramic fiber filter on DPF (Diesel Particulate Filter) system and experiments were performed to select appropriate filter which can filter particulates. Filters were installed on metal -support tube which has openings for exhaust gas flow. Ceramic fiber filters with high specific surface area and adequate high temperature strength are commercially available for filtration of diesel particulates and in -situ hot regeneration. Thus, ceramic blanket and ceramic board which are used as insulating media were applied to filter and filtration apparatus was installed on exhaust gas line connected to 2.0 L diesel engine. Alternating filter structure to adapt DPF system, collection efficiency test of diesel particulates was measured. In case of ceramic blanket, pressure drop was low, caused by the destruction of soft structures. Also, particulate collection efficiency was decreased depending on loading time. In case of ceramic board, structure design was altered to reduce back pressure on DPF system. Structure design was altered to induce Z-flow by making 10 mm and 5 mm holes on the surface of media. Alteration of 5 mm hole showed that media have low back pressure but particulate collection efficiency was 77%, while 10 mm hole showed that of 90%.