• Journal of the Korean Ceramic Society
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• v.51 no.6
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• pp.533-538
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• 2014

Today, silicon and epoxy resin are used as materials of conversion lenses for white LEDs on the basis of their good bonding and transparency in LED packages. But these materials give rise to long-term performance problems such as reaction with water, yellowing transition, and shrinkage by heat. These problems are major factors underlying performance deterioration of LEDs. In this study, in order to address these problems, we fabricated a conversion lenses using glass, which has good chemical durability and is stable to heat. The fabricated conversion lenses were applied to a remote phosphor type. In this experiment, the conversion lens for white LED was coated on a glass substrate by a screen printing method using paste. The thickness of the coated conversion lens was controlled during 2 or 3 iterations of coating. The conversion lens fabricated under high heat treatment temperature and with a thin coating showed higher luminance efficiency and CCT closer to white light than fabricated lenses under low heat treatment temperature or a thick coating. The conversion lens with $32{\mu}m$ coating thickness showed the best optical properties: the measured values of the CCT, CRI, and luminance efficiency were 4468 K, 68, and 142.22 lm/w in 20 wt% glass frit, 80 wt% phosphor with sintering at $800^{\circ}C$.

• Journal of the Korean Ceramic Society
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• v.53 no.5
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• pp.529-534
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• 2016

Nanocrystalline powder of zirconia stabilized with 8 mol% yttria (YSZ) has been synthesized through oxalate process using $ZrOCl_2{\cdot}8H_2O$ and $Y(NO_3)_3{\cdot}6H_2O$ as starting materials. Understanding of the characteristic changes of YSZ powder as a function of processing conditions is crucial in developing dense and porous microstructures required for fuel cell applications. In this research, microstructure change, surface area, particle shape and particle size were measured as a function of different processing conditions such as calcination temperature, stirring speed and concentration of starting materials. The resultant crystallite sizes were calculated by XRD-LB (X-Ray Diffraction Line-Broadening) method, BET method, and morphology of the crystal was observed in TEM and FE-SEM. The TEM examination showed that the powder synthesized with 0.7 M of YSZ concentration had a spherical morphology with sizes ranging from 20 to 40 nm. However, the powder was gradually aggregated above 1.0 M of YSZ concentration with the aggregation being intensified as the YSZ concentration was increased.

• Tribology and Lubricants
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• v.8 no.2
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• pp.64-72
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• 1992

The recent trends of rotating machinery demand high speed and high temperature operation, and the bearing with new material is required to be developed. Ceramic, especially silicon nitride, have been receiving attention as alternative material to conventional bearing steel. Ceramic ball bearing offers major performance advantages over steel bearing, for instance, high speed, maginal lubrication, high temperature, improved corrosion resistance and nonmagnetic capabilities etc.. In this paper, the mechanical characteristics of ceramic ball bearing (hybrid ceramic bearing and all ceramic bearing) were investigated, and the characteristics of ceramic bearing were compared with that of steel bearing. Deep groove ball bearing 6208 was taken the object of analysis. The main results of analysis were followings: the radial stiffness of hybrid and all ceramic bearing were 112% and 130% that of steel bearing, and the axial stiffness of all ceramic bearing was 110% that of steel bearing. According as rotating speed was up, the ball load, the contact angle, the contact stress and the spin-to-roll ratio between ball and raceway of ceramic bearing were far smaller than these of steel bearing. And there was not a significant difference between the minimum film thickness of ceramic bearing and steel bearing. It is expected that this research is contributed to enhanced fundamental technology for the practical applications of ceramic ball bearing.

• Korean Journal of Materials Research
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• v.27 no.1
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• pp.43-47
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• 2017

E (Electric) -glass fibers are the most widely used glass fibers, taking up 90 % of the long glass fiber market. However, very few papers have appeared on the physical characteristics of E-glass fibers and how they depend on the fiberizing temperature of fiber spinning. Glass fiber was fabricated via continuous spinning process using bulk E-glass. In order to fabricate the E-glass specimen, raw materials were put into a Pt crucible and melted at $1550^{\circ}C$ for 2hrs; mixture was then annealed at $621{\pm}10^{\circ}C$ for 2hrs. The transmittance and adaptable temperature for spinning of the bulk marble glass were characterized using a UV-visible spectrometer and a viscometer. Continuous spinning was carried out using direct melting spinning equipment as a function of the fiberizing temperature in the range of $1175{\sim}1250^{\circ}C$, while the winder speed was fixed at 500 rpm. Subsequently we investigated the physical properties of the E-glass fiber. The average diameter of the synthesized glass fiber was measured by optical microscope. The mechanical properties of the fiber were confirmed using a UTM (universal materials testing machine); the maximum tensile strength was measured and found to be $1843{\pm}449MPa$ at $1225^{\circ}C$.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2005.11a
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• pp.66-69
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• 2005

Mechanical strength of functionally graded composite plates that composed of ceramic, functionally graded material and metal layers is investigated using 3-D finite element method. In FGM layer, material properties are assumed to be varied continuously in the thickness direction according to a simple power law distribution in terms of the volume fraction of a ceramic and metal. The 3-D finite element model is adopted by using an IS-node solid element to analyze more accurately the variation of material properties in the thickness direction. Numerical results are compared with those of the previous works. In addition, the displacements, the tensile stresses and the compressive stresses are analyzed for the variation of FGM thickness ratio and volume fraction distribution.Mechanical strength of functionally graded composite plates that composed of ceramic, functionally graded material and metal layers is investigated using 3-D finite element method. In FGM layer, material properties are assumed to be varied continuously in the thickness direction according to a simple power law distribution in terms of the volume fraction of a ceramic and metal. The 3-D finite element model is adopted by using an IS-node solid element to analyze more accurately the variation of material properties in the thickness direction. Numerical results are compared with those of the previous works. In addition, the displacements, the tensile stresses and the compressive stresses are analyzed for the variation of FGM thickness ratio and volume fraction distribution.

• 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 Architectural Institute of Korea Structure & Construction
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• v.35 no.12
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• pp.149-156
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• 2019

Recently, skyscraper building and apartment fires, which were rapidly spread out from a low floor to a rooftop, have become a frequent occurrence in mass media. This fire problems have a fatal disadvantage that the exterior wall finish of the building emits toxic gas in case of fire by using dry bit method or organic insulating material. Therefore, in order to remedy these problems, many exterior wall finishing construction methods have been proposed, but the current trend is to use existing construction methods due to problems such as economy, weight, and durability. On the other hand, in countries such as Germany and Japan, ceramic sidings are used as exterior finishing material for buildings, which is environmentally friendly, excellent natural beauty, long life, easy maintenance and high-quality exterior materials. However, those ceramic sidings have still the problems such as manufacturing cost and weight problem because of boosting the sintering temperature up to 1,350℃ or more. Also, conventional CRC, MgO, FRP sidings which are composed of pulp, glass fiber and organic materials, have been reports of deformation due to ultraviolet rays, discoloration, corrosion and scattering, surface rupture, lifting and peeling. Therefore, in this study as an alternative to solve this problem, halosite nano kaolin produced in Sancheong in Korea and frit flux were used to satisfy the required properties as ceramic siding using low temperature sintering (below 1,000℃) and lightweight materials such as pearlite. This study aims to design the optimal formulation and process of materials and to study the characteristics of nano-coated ceramic siding material development and to present relevant basic data. The findings show that ceramic siding for nanocoated building materials is excellent as a natural ceramic siding building material. The fire resistance of natural minerals and nano particle refining technology satisfy the bending strength of 80kgf / cm2, the volume ratio of 2.0 and the absorption rate of less than 10.0%.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.06a
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• pp.388-389
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• 2009

The use of arc tubes made of ceramic material further enhanced some of the metal halide lamp's properties. These properties translate into higher efficacy with better color rendering, stable color through lamp long life. Recently, due to an increase in the application of the ceramic metal-halide lamp, the study for the property etc. according to Ballast's driving scheme and the study for arc tube material, optimization of gas and so on are being proceeded to improve the property of the lamp. Especially, to control ceramic metal-halide lamp, the vigorous study and practical use with respect to Electronic Ballast, which has been improved in the disadvantages of the conventional Magnetic Ballast are made. In this paper, Electrical characteristics and gas insulation destroy time are analyzed by comparing magnetic ballast with electronic ballast.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.07b
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• pp.686-689
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• 2002

The application of the ultrasonic nozzle has been extended because it is possible atomization of liquid material. In this study, the characteristics of the ultrasonic nozzle and ceramic oscillator were investigated. The oscillator for the ultrasonic nozzle were made piezoelectric ceramic of $Pb[(Sb_{1/2}Nb_{1/2})_{0.035}-(Mn_{1/3}Nb_{2/3})_{0.065}-(Zr_{0.49}Ti_{0.51})_{0.90}]O_3$. The electromechanical coupling factor$(k_p)$ and mechanical quality factor$(Q_m)$ showed the values of 0.555, 1,214 respectively when the Zr/Ti ratio was 49/51. Moreover, this oscillator will have the temperature stability because it's curie temperature is $322[^{\circ}C]$. The driving current of ultrasonic nozzle showed the value of 80[mA] when the driving time was 10[min.]. Also, The surface temperature of ceramic oscillator showed $80[^{\circ}C]$ at driving time 10[min.] We knew that the ultrasonic nozzle had stabile driving above 10[min.].

• Journal of the Korean Society of Physical Medicine
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• v.10 no.1
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• pp.91-97
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• 2015

PURPOSE: In this study investigated the thermal effect in tissue mimicking phantom by the material of the ultrasonic transducer in low intensity sonication. METHODS: The material of the ultrasonic transducer was made of ceramic, stainless steel, aluminum. Korea Testing Laboratory was measured of the three kinds of materials the total output of the ultrasonic transducer. Each material was measured core temperature and the actual output depending on the type of transducer. Agarose tissue mimicking phantom and silicone tissue mimicking phantom was made. Transducers made of three kinds of materials were emitted in the phantom. It is shown as a graph about time and temperature and the surface temperature rising speed and deep temperature rise rate was investigated. RESULTS: Ceramic transducers were highest output. Higher than the stainless steel transducer, aluminum had the lowest total output. Deep temperature was the highest in the ceramic transducer, and the surface temperature was the highest in the stainless steel transducer. Thermal images of ceramic transducer showed that a valid output is formed deeper wider than the metal. CONCLUSION: Ceramic transducer is confirmed the excellence than the metal transducer in deep thermal effect and the actual output of the ultrasound.