• 한국분말재료학회지
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• 제29권6호
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• pp.477-484
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• 2022

Thermal protection systems (TPS) are a group of materials that are indispensable for protecting spacecraft from the aerodynamic heating occurring during entry into an atmosphere. Among candidate materials for TPS, ceramic insulation materials are usually considered for reusable TPS. In this study, ceramic insulation materials, such as alumina enhanced thermal barrier (AETB), are fabricated via typical ceramic processing from ceramic fiber and additives. Mixtures of silica and alumina fibers are used as raw materials, with the addition of B4C to bind fibers together. Reaction-cured glass is also added on top of AETB to induce water-proof functionality or high emissivity. Some issues, such as the elimination of clumps in the AETB, and processing difficulties in the production of reusable surface insulation are reported as well.

• Journal of Ceramic Processing Research
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• 제13권spc1호
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• pp.145-148
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• 2012

Spherical silica aerogel powders were fabricated via an emulsion polymerization method from a water glass. A water-in-oil emulsion, in which droplets of a silicic acid solution are emulsified with span 80 (surfactant) in n-hexane, was produced by a high power homogenizer. After gelation, the surface of the spherical silica hydrogels was modified using a TMCS (trimethylchlorosilane)/n-hexane solution followed by solvent exchange from water to n-hexane. Hydrophobic silica wet gel droplets were dried at 80 ℃ under ambient pressure. A perfect spherical silica aerogel powder between1 to 12 ㎛ in diameter was obtained and its size can be controlled by mixing speed. The tapping density, pore volume, and BET surface area of the silica aerogel powder were approximately 0.08 g·cm-3, 3.5 ㎤·g-1 and 742 ㎡·g-1, respectively.

• Journal of Ceramic Processing Research
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• 제13권spc2호
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• pp.363-367
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• 2012

DLC (diamond liked carbon) coating of the tungsten carbide (WC) alloy core surface for molding a glass aspheric lens improves the quality of glass lens and the molding core and is characterized by high hardness, high elasticity, abrasion resistance and chemical stability. In this study, the effect of DLC coating of a thin film by means of the filtered AIP (arc ion plating) technique was examined on Ra and shape of the coated surface. Roughness before and after DLC coating was measured and the result showed that the roughness was improved after coating as compared to before coating. It was observed that DLC coating of the WC alloy core surface for molding had an effect on improving the roughness and shape of the core surface. It is considered that this will have an effect on improving abrasion resistance and the service life of the core surface.

• 소성∙가공
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• 제11권7호
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• pp.608-613
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• 2002

An ultrasonic machining process is efficient and economical means for precision machining of glass and ceramic materials. However, the mechanism of the process with respect to the crack initiation and propagation and the stress development in the ceramic workpiece subsurface arc still not well understood. In this research, we have investigated the basic mechanism of ultrasonic machining of ultrasonic machining of glass by the experimental approach. For this purpose, we designed and fabricated the desktop micro ultrasonic machine. The feed is controlled precisely by using the constant load control system. During machining experiments, the effects of abrasive characteristics and machining conditions on the surface roughness and the material removal rate are measured and compared.

• 한국레이저가공학회:학술대회논문집
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• 한국레이저가공학회 2004년도 추계학술대회논문집
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• pp.50-61
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• 2004

Nowadays Laser Controllable Thermo-cleaving is the most promising method of cutting FPD(Flat Panel Display) glass in mass-production line. And this method can be used to cut other brittle materials such as quartz, sapphire, ceramic and semiconductor. The concept of this method is shown in Picture 1. Laser beam heats glass up to strain point not to melting point and cooling system chills glass to make maximum thermal stress in glass and then the thermal stress generates micro thermal crack in other words blind crack. Laser Controllable Thermo-cleaving controls the thermal stress to optimize the blind crack up to level of mass-production line.

• Journal of Ceramic Processing Research
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• 제19권5호
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• pp.394-400
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• 2018

The current work investigates the effects of nucleation heat treatments, on the microstructure and mechanical properties of a novel silicate glass in $Li_2O-BaO-SiO_2$ system with 1 mol% $P_2O_5$ as nucleating agent. As-cast glass was exposed to nucleation heat treatments at $490-550^{\circ}C$ for 1-3 h. The microstructural examination was performed by SEM/EDS. The highest Vickers microhardness was determined to be 650 Hv for the sample heat treated at $550^{\circ}C$ for 1 h. The increase in the nucleation time also affected Vickers microhardness and the highest one was determined to be 600 Hv after nucleation for 3 h. The fracture toughness, $K_{IC}$ reached $2.51MPa.m^{1/2}$ after nucleation at $550^{\circ}C$ for 1 h. The nucleation temperatures had a more pronounced effect on the fracture toughnesses in comparison to nucleation times. The indentation toughness data was used to determine Weibull parameters from Ln ln [1/(1-P)]-$lnK_{IC}$ plots. Weibull modulus, m of the samples nucleated at 500, 510, 530, $550^{\circ}C$ for 1h. and $540^{\circ}C$ for 2 h. were determined similarly to be 3.8, 3.5, 4.7 and 3.9, respectively. The rest of the samples indicated higher Weibull moduli, which may be attributed to the formations of microcracks due to the mismatch in between newly formed crystals and remaining glassy matrix.

• 한국세라믹학회지
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• 제40권10호
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• pp.936-942
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• 2003

In order to develop glass formulations for vitrifying Low-and Intermediate-Level radioactive Wastes (LILW) from nuclear power plants of Korea Hydro & Nuclear Power (KHNP) Co., Ltd., promising glass formulations were selected based on glass property model predictions for viscosity, electrical conductivity and leach resistance. Laboratory measurements were conducted to verify the model predictions. Based on the results, the models for electrical conductivity, US DOE 7-day Product Consistency Test (PCT) elemental release, and pH of PCT leachate are accurate for the LILW glass formulations. However, the model for viscosity was able to provide only qualitative results. A leachate conductivity test was conducted on several samples to estimate glass leach resistance. Test results from the leachate conductivity test were useful for comparison before PCT elemental release results were available. A glass formulation K11A meets all the KHNP glass property constraints, and use of this glass formulation on the pilot scale is recommended. Glass formulations K12A, K12B, and K12E meet nearly all of the processing constraints and may be suitable for additional testing. Based on the comparison between the measured and predicted glass properties, existing glass property models may be used to assist with the LILW glass formulation development.

• 한국세라믹학회지
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• 제40권7호
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• pp.644-651
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• 2003

첨가물의 형태가 X7R용 MLCC 유전 원료의 전기적 특성 및 미세구조에 미치는 영향을 평가하였다. Glass frit 및 산화물 형태로 제조된 첨가물을 분말 공정 조건을 달리하여 동일한 주조성에 첨가하였다. 미세구조 및 유전특성을 측정한 결과, glass 층에 dopant의 농도 구배가 존재하는 조성이 유전 특성이 가장 우수하였다. 최적 조성을 MLCC로 제작하여 유전 특성을 측정하였으며, X7R 제반 조건을 만족하였다.

• 한국결정성장학회:학술대회논문집
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• 한국결정성장학회 1998년도 PROCEEDINGS OF THE 15TH KACG TECHNICAL MEETING-PACIFIC RIM 3 SATELLITE SYMPOSIUM SESSION 4, HOTEL HYUNDAI, KYONGJU, SEPTEMBER 20-23, 1998
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• pp.79-83
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• 1998

Plasma display panel is a potential candidate for HDTV, due to the fact hat the expansion of screen size is much easier using thick film technology. In this study, transparent dielectric materials using lead borosilicate glasses is developed, which satisfy the requirements of dielectrics for PDP. Paste is made of this glass composition. The paste has thixotropic behavior suitable for screen printing. The paste shows more thixotropic behavior as the particle size decrease. After firing, cross sectional area was analyzed by SEM. The void of fired thick film was removed using bimodal particle system. The dielectric showed good adhesion characteristics.

• 한국결정성장학회지
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• 제9권1호
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• pp.50-54
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• 1999

플라즈마 디스플레이는 후막기술을 이용하여 화면의 크기를 늘리는 것이 쉽기 때문에 고선명 TV의 가장 유력한 후보이다. 본 연구에서는 플라즈마 디스플레이용 유전체의 조건을 만족하는 lead borosilicate 유리를 이용한 투명 유전체 재료를 개발하였다. 또한 이 유리를 이용하여 페이스트를 제조하였다. 페이스트는 스크린 프린팅에 적합한 요변성을 나타내었고, 입자 크기가 작아질수록 더욱 강한 요변성을 나타내었다. 열처리 후 후막의 파단면을 전자현미경으로 관찰하였다. 후막의 기공은 서로 다른 크기의 평균입경을 갖는 powder를 사용함으로써 제거 될 수 있었다. 소성된 후막은 좋은 융착 특성을 나타내었다.