• The Journal of Korean Academy of Prosthodontics
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• v.23 no.1
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• pp.113-123
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• 1985

The purpose of this study was to evaluate the marginal fitness of collarless metal-ceramic crown formed with direct lift technique using wax compared with metal-ceramic crown with metal butt margin. Twenty crowns, ten were collarless metal-ceramic crowns and ten were metal-ceramic crowns with metal butt margins, were made and cemented on epoxy resin dies, and their marginal openings were measured on scanning electron microphotographic prints at x200 magnification. The results were as follows; 1. In the case of collarless metal-ceramic crowns, the mean marginal opeining was $43.78{\pm}17.67{\mu}m$, the mean maximum marginal opening was $52.81{\pm}19.81{\mu}m$, and the mean minimum marginal opening was $34.99{\pm}16.58{\mu}m$. 2. In the case of metal-ceramic crowns with metal butt margins, the mean marginal opening was $47.62{\pm}25.55{\mu}m$, the mean maximum marginal opening was $61.90{\pm}24.39{\mu}m$, and the mean minimum marginal opening was $34.86{\pm}24.92{\mu}m$. 3. There was no significant difference between two types of crowns at the 99% confidence level. 4. The marginal fitness of collarless metal-ceramic crown formed with direct lift technique using wax was clinically acceptable.

• Journal of the Korean Ceramic Society
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• v.45 no.11
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• pp.719-724
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• 2008

Every concrete structure should continue to perform its intended functions such as to maintain the required strength and durability during its lifetime. Deterioration of the concrete structure, however, occurs more progressively from the outside of the concrete exposed to severe conditions. Main deteriorations in concrete structures result from carbonation, chloride ion attack and frost attack. Concrete can therefore be more durable by applying surface protection to increase its durability using impregnants, which are normally classified into two large groups in polymeric and silicate materials. Concrete impregnants are composed of silanes and alkali silicates (sodium, potassium and lithium silicate). Thus, this study is concerned with elevating the carbonation and Cl- penetration resistance of concrete structures by applying alkali silicate hydrophilic impregnants including lithium and potassium silicates. From the experimental test results, lithium and potassium silicates produced a good improvement in carbonation resistance and are expected to be used as hydrophilic impregnants of concrete structures.

• Journal of the Korean Ceramic Society
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• v.51 no.4
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• pp.332-336
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• 2014

A non-electric water purification system using the Korean traditional ceramic ware Onggi, was demonstrated as an appropriate technology to solve water shortages in under developed regions. Generally, Onggi is produced using large size raw materials that are sintered at low temperature, resulting in a porous body that shows air and water permeability. An Onggi filter was prepared using a spinning wheel with the addition of rice bran to the body to increase porosity. The porosity of the obtained Onggi filter was 25.1%; the water permeability was 85.1 $L/m^2h$. Turbidity and TDS of the purified water using Onggi filter were decreased by 97.7% and 29.1%, respectively.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.13 no.3
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• pp.301-307
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• 2002

A multilayer ceramic chip antenna with helical structure is analyzed to enhance the narrow bandwidth of conventional ceramic chip antennas. The simulations are performed by HFSS to verify the effects of structural parameters on impedance bandwidth. The multilayer ceramic chip antennas consist of a rectangular-parallelepiped ceramic body$({\varepsilon}_r=7.8,\; tan\; {\delta}=0.0043)$ and helical conductor patterns are embedded in the ceramic body using LTCC-MLC technology. 3D structure design of the multilayer ceramic chip antenna suitable for IMT-2000 (1,920~2,170 MHz) handset has been implemented, and experimental results are presented and discussed.

• Journal of Powder Materials
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• v.17 no.3
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• pp.230-234
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• 2010

Homogenous silica-coated $CoFe_2O_4$ samples with controlled silica thickness were synthesized by the reverse microemulsion method. First, 7 nm size cobalt ferrite nanoparticles were prepared by thermal decomposition methods. Hydrophobic cobalt ferrites were coated with controlled $SiO_2$ using polyoxyethylene(5)nonylphenylether (Igepal) as a surfactant, $NH_4OH$ and tetraethyl orthosilicate (TEOS). The well controlled thickness of the silica shell was found to depend on the reaction time and the amount of surfactant used during production. Thick shell was prepared by increasing reaction time and small amount of surfactant.

• Journal of the Korean institute of surface engineering
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• v.49 no.6
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• pp.507-512
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• 2016

Expensive silver powder is used to form electrodes in most IT equipment, and recently, many attempts have been made to lower manufacturing costs by developing powders with Ag-Ni or Ag-Cu core-shell structures. This study examined the sintering behavior of Ag-Ni electrode powder with a core-shell structure for silicon solar cell with high energy efficiency. The electrode powder was found to have a surface similar to pure Ag powder, and cross-sectional analysis revealed that Ag was uniformly coated on Ni powder. Each electrode was formed by sintering in the range of $500^{\circ}C$ to $800^{\circ}C$, and the specimen sintered at $600^{\circ}C$ had the lowest sheet resistance of $5.5m{\Omega}/{\Box}$, which is about two times greater than that of pure Ag. The microstructures of electrodes formed at varying sintering temperatures were examined to determine why sheet resistance showed a minimum value at $600^{\circ}C$. The electrode formed at $600^{\circ}C$ had the best Ag connectivity, and thus provided a better path for the flow of electrons.

• Journal of Technologic Dentistry
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• v.33 no.1
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• pp.7-14
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• 2011

Purpose: As the demand and importance of aesthetic aspects in dental treatment become higher, much attention is paid to materials used for dental prostheses. Thus, the marginal fidelity of most-commonly used alloy, IPS - Empress and ZrO2 ceramic is compared. Methods: The alloy core made by casting, IPS - Empress core made by pressing and ZrO2 ceramic core made by CAD/CAM are used to make 10 samples respectively. For each core, three points were measures and the optical microscope (Axio Imager.Alm,Zeiss co., Oberkochen, Germany) was used to observe the cores with a magnification of 100. Results: As for alloy, IPS - Empress and ZrO2 ceramic, the average and deviation of their marginal distance are $29.91\;{\pm}11.93{\mu}m$ for alloy, $33.45\;{\pm}8.61{\mu}m$ for IPS - Empress, and $31.55\;{\pm}9.85{\mu}m$ for ZrO2. The one-way ANOVA test was conducted to compare them. However, there was no statistically significant difference among them. Conclusion: The study on marginal fidelity of alloy, IPS - Empress, and ZrO2 ceramic shows they have no marginal fidelity problem clinically. Therefore, if a system is selected based on the patient's condition or treatment method, there will be no problem.

• The Journal of Korean Academy of Prosthodontics
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• v.38 no.4
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• pp.461-471
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• 2000

This study evaluated the effect of degassing on the ceramic bond strength of two Ni-Cr alloys under varying holding time at the upper limit temperature and atmospheric conditions. Metal specimens were divided into 5 groups for each alloy according to degassing conditions prior to porcelain application no degassing, degassing under vacuum without hold, degassing under vacuum with hold for 5 min. and 10 min. respectively at the upper limit temperature and degassing in air. Total number of metal ceramic specimens was eighty and each group had eight specimens. The ceramic bond strength was measured by four-point flexural test using Instron and the fractured surface was examined under SEM. The results obtained were as follows. 1. Degassing in air improved the ceramic bond strength of Ni-Cr alloys. 2. In degassing under vacuum, hold at the upper limit temperature was advantageous to the ceramic bonding of Ni-Cr alloys. 3. After ceramic metal bond test, metal surfaces were partially covered with the thin porcelain layer, and the cohesive failures in porcelain were predominant in groups showing higher ceramic bond strength.

• Journal of Ocean Engineering and Technology
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• v.10 no.2
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• pp.106-119
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• 1996

The ceramic has various high mechanical properties such as heat, abrasion, corrosion resistance and high temperature strength compared with metal. It also has low speciffic weight, low thermal expansibillity, low thermal conductivity. However, it could not be used as structural material since it is brittle and difficult for the machining. Therefore, there have been many researches to attempt to join ceramic with metal which is full of ductillity in order to compensate the weakness of ceramic.The problem is that residual stress develops around the joint area while the ceramic/metal joint material is cooled from high joining temperature to room temperature due to remarkable difference of thermal expansion coefficients between ceramic and metal. Especially, the residual stress at both edges of the specimen reduces the strngth of joint to a large amount by forming a singular stress field. In this study, two dimensional finite element method is attempted for the thermal elastic analysis. The joint residual stress of ceramic/metal developed in the cooling process is investigated and the change of joint residual stress resulted from the repetitive heat cycle is also examined. In addition, it is attempted to clarify the joint stress distribution of the case of tensile load and of the case of superposition of residual stress and actual loading stress.

• Journal of the Korean Ceramic Society
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• v.44 no.11
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• pp.622-626
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• 2007

Graphite is widely used in electronic industry due to its excellent electrical and thermal properties. However, graphite starts to oxidize around $400^{\circ}C$ that seriously degrades its properties. SiC coating can be applied to graphite foam to improve its high temperature oxidation resistance. In this research, SiC coating on graphite foam was made via preceramic polymer using a polyphenylcarbosilane. 20% of polyphenylcarbosilane in hexane solution was coated onto graphite by dip coating method. Thermal oxidation was carried out at $200^{\circ}C$ for crosslink of the preceramic polymer and the sample were pyrolysized at $800^{\circ}C{\sim}1200^{\circ}C$ under nitrogen to convert the preceramic polymer to SiC film. The microstructure of the SiC coating after pyrolysis was investigated using FESEM and oxidation resistance up to $800^{\circ}C$ was evaluated.