초록 ▼

1. 비접촉식 가스부양장비 개발
·비접촉식 가스부양장비를 국내에서 최초로 개발에 성공
·안정적인 부양을 위해 유체역학에 기초한 노즐 설계기술을 확립
·레이저 파워제어와 실시간 데이터 수집처리를 위한 LabView 프로그래밍 개발
·공정변수의 최적화(구형시편의 최적제조조건, 산소가스의 유량제어, CO₂ laser 출력제어)
2. 준안정 세라믹제조, 미세조직 및 물성평가
·In-situ 냉각곡선으로부터 유추된 응고기구 해석
·용융 세라믹의 고온 열물성(고온 밀도, 열팽창계수) 평

1. 비접촉식 가스부양장비 개발
·비접촉식 가스부양장비를 국내에서 최초로 개발에 성공
·안정적인 부양을 위해 유체역학에 기초한 노즐 설계기술을 확립
·레이저 파워제어와 실시간 데이터 수집처리를 위한 LabView 프로그래밍 개발
·공정변수의 최적화(구형시편의 최적제조조건, 산소가스의 유량제어, CO₂ laser 출력제어)
2. 준안정 세라믹제조, 미세조직 및 물성평가
·In-situ 냉각곡선으로부터 유추된 응고기구 해석
·용융 세라믹의 고온 열물성(고온 밀도, 열팽창계수) 평가
·미세구조 관찰 및 물리적 특성 평가
- 밀도측정, 상 동정, - 준안정구조의 해석, 열물성, 굴절률 평가
- 성분 분석(EPMA) 및 응고조직 관찰 및 해석
3. 고굴절률을 갖는 BaO-TiO₂계 광학소재 개발
·굴절률 2.0이상 소재 개발, 광발광 특성평가 및 메카니즘 규명
4. 큰 사이즈의 볼렌즈 개발을 위한 가스 부양로 개발
·직경이 약 7 mm 인 고굴절률 구형유리개발
·고부가가치의 광학렌즈, 인조 다이아몬드 등에 응용가능

Abstract ▼

Containerless levitation technique is of interest field because it enables sample be melted and solidified without a container. Melting experiments under microgravity provides a peculiar environment characterized by no thermally-induced convection, no sedimentation/buoyancy and non-contact with vess

Containerless levitation technique is of interest field because it enables sample be melted and solidified without a container. Melting experiments under microgravity provides a peculiar environment characterized by no thermally-induced convection, no sedimentation/buoyancy and non-contact with vessel walls. Because a melting experiment under the microgravity environments incurs a high cost, it is an essential prerequisite to conduct a ground-based melting experiment using a levitation technique. In the present study, the aerodynamic levitator was successfully developed. In order to maintain stable levitation, conical nozzle was designed from a hydraulic point of view. Laser power control and data acquisition was conducted using the LabView program. The processing parameters for levitaion technique was optimized. To develop a new high-functional material with novel physical properties, (Ba,Sr)TiO₃ ceramics was prepared by aerodynamic levitation. The (Ba,Sr)TiO₃ ceramics is expected to represent excellent electrical and dielectric properties due to metastable structure, which can't be obtained by a conventional materials processing routes. Studies of the liquid state are important for technological applications because the molten state is an essential stage in many industrial processes, such as glass making, single-crystal growth, iron- and steel-making industry, etc. Nevertheless, there is little data on the density of molten ceramics due to the experimental difficulties in classical density measurements at high temperatures due to the unavoidable chemical reactions with the containers. The thermophysical properties of (Ba,Sr)TiO₃ materials, such as the density and volumetric thermal expansion coefficient was determined effectively using aerodynamic levitation technique. On the other hand, the growth behavior of solid phase is an important event during liquid-solid phase transformation, which influences the subsequent solidification, the final structures and properties of the material. However, there was no detailed analysis of transformation kinetics during recalescence in literature. In this study, semiconducting (Ba,Sr)TiO₃ ceramics were solidified using aerodynamic levitator and the solidification behavior during recalescence and microstructure of the levitated (Ba,Sr)TiO₃ ceramic were investigated in detail. Almost-spherical yttrium aluminum garnet (Y₃Al₅O₁₂,YAG) was synthesized using an aerodynamic levitator. The formation of crystalline or glass-ceramic depended on the initial mass of the molten droplet. The YAG was devitrified due to partial crystallization, even after rapid quenching, indicating a high tendency for crystallization. It was found that YO₃-Al₂O₃ melt represented a polyamorphic liquid-liquid phase transition. The optical transparency of YAG increased with increasing Eu³⁺content because of the reduced number of micro-sized crystals, which act as a scattering center to visible light. The photoluminescence intensity of the YAG:Eu glass-ceramic was attributed mainly to an electric dipole⁵D₀→⁷F₂ transition because the Eu³⁺in the YAG glass-ceramicis located at sites with low symmetry. On the other hand, in order to develop the excellent optical materials, spherical TiO₂-rich glasses (BaTi₃O₇, Ba₆Ti₁₇O₄₀, Ba₄Ti₁₃O₃₀) were prepared by aerodynamic levitator. Colorless and transparent BaTi₃O₇-20% SiO₂, Ba(Ti_0.8Zr_0.2)₃O₇, (Ba_1-xEu_x)₆(Ti_0.8Zr_0.2)₁₇O₄₀, and (Ba_1-xEu_x)₄(Ti_0.8Zr_0.2)₁₃O₃₀ glasses were prepared successfully. The glasses represented high refractive index more than 2.0. The Abbe number was also higher than 20, indicating potential candidates for future optical materials application, such as camera lenses. Finally, containerless aerodynamic levitation processing is a unique technology for the fabrication of bulk non-crystalline materials. Using conventional aerodynamic levitation, a high reflective index (RI) material (BaTi₂O₅ and LaO_3/2-TiO₂-ZrO₂system) was developed with a RI greater than approximately 2.2, which is similar to that of diamond. However, the glass size was small, approximately 3 mm in diameter. Therefore, it is essential to produce large sized materials for future optical materials applications, such as camera lenses. In this study, a new aerodynamic levitator was designed to produce large-sized non crystalline materials, more than 6 mm in diameter. The concept of this new levitator is to set up a reduced pressure at the top of the molten samples without generating turbulent flow. A numerical simulation was also performed to verify the concept. Overall, this study can provide design and manufacturing methodologies of new functional materials having metastable phase and outstanding properties.