• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.06a
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• pp.32-35
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• 2006

For the white UV-LED applications, $Eu^{2+}$-activated calcium aluminium silicate phosphors were synthesized for the first time and the structures and luminescence characteristics of these phosphors were investigated. The phosphors in this study emitted blue. green or blue-green light depending on the starting materials for synthesis. In addition, the structure was also changed when the different starting materials were used. When CaO and $CaCO_3$ was used as a starting material. tetragonal $Ca_2Al_2SiO_7$ was formed and blue-green and pure green light was emitted. respectively. However. in the case of $CaSiO_3$, triclinic $CaAl_2Si2O_8$ was formed and only pure blue emission was detected. The maximum emission intensity was obtained from $CaAl_2Si_2O_8:Eu^{2+}$ phosphors, which intensity was about 1.4 times higher than that of YAG:$Ce^{3+}$ phosphor used for blue LED.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.08a
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• pp.164-164
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• 2013

최근에 희토류 이온이 치환 고용된 실리케이트계 형광체를 발광 소자, 레이저, 광전 소자에 응용하기 위한 연구에 많은 관심이 집중되고 있다. 본 연구에서는 고상 반응법을 사용하여 초기 물질 CaO (99.99% 순도), SiO2 (99.99%), RE2O3 (RE=Sm3+, Tb3+, 99.9%)을 화학 적량으로 준비하여 활성제 이온 Sm3+과 Tb3+이온의 함량비를 0, 0.01, 0.05, 0.10, 0.20 mol로 변화시켜 Ca2SiO4:RE3+ 형광체를 제조하여 그것의 발광과 흡광 특성을 조사하였다. Sm3+ 이온이 도핑된 Ca2SiO4 형광체의 경우에, 발광 스펙트럼은 Sm3+ 이온의 함량비에 관계없이 모든 시료에서 602 nm에 피크를 갖는 강한 주황색 발광 스펙트럼, 상대적으로 발광 세기가 약한 569 nm에 정점을 갖는 황색 발광과, 652 nm와 711 nm에 피크를 갖는 적색 발광 스펙트럼이 관측되었다. Sm3+ 이온의 함량비가 0.01 mol 일 때 세 영역의 발광 스펙트럼의 세기는 최대값을 나타내었다. Sm3+ 이온의 함량비가 증가함에 따라 모든 발광 스펙트럼의 세기는 순차적으로 감소하였다. 이 현상은 농도 소광 현상에 기인함을 알 수 있었다. Sm3+ 이온이 도핑된 형광체 분말의 경우에, 주 흡광 스펙트럼은 Sm3+ 이온의 함량비에 관계없이 408 nm에서 관측되었으며, 이밖에도 상대적으로 흡광 세기가 약한 349 nm, 367 nm, 476 nm에서 흡광이 발생하였다.

• Journal of the Korea institute for structural maintenance and inspection
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• v.14 no.1
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• pp.71-77
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• 2010

The concrete structure's durability and integrity is reduced owing to various deterioration phenomena. Therefore, it is important to prevent the deterioration phenomena. This study inquired into the various experimental results of specimens with different dilution concentration and impregnation time by the each solution to present the economic and efficient using method of the inorganic surface penetration agents. As a results, the reasonable dilution concentration and impregnation time of colloidal silica solutions are 15% and 5 minute and for the sodium alumina silicate solutions are 17% and 10 second.

• Journal of the Korean institute of surface engineering
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• v.54 no.6
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• pp.331-339
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• 2021

Environmental barrier coatings(EBCs) are applied to the SiC/SiC ceramic matrix composites(CMCs) in order to protect CMCs from being corroded with water vapor by combustion gas in gas turbine engines. Ytterbium silicates, such as ytterbium monosilicate and ytterbium disilicate, are ones of the candidate materials for EBCs due to their excellent resistance to water vapor corrosion as well as thermal-expansion match with SiC. In this study, ytterbium silicates are fabricated with 2-step solid-state synthesis targeting ytterbium disilicate. After synthesizing ytterbium monosilicate, the mixtures of ytterbium monosilicate and SiO₂ are heat-treated and densified by using pressureless sintering or hot pressing with a variety of heating conditions. The phase formation, thermal expansion, and oxidation behavior are examined with fabricated specimens. The final densified bodies are found to be composites between ytterbium monosilicate and ytterbium disilicate with different ratios, which results in 4.43 to 6.72×10^-6/K range of coefficients of thermal expansion. The probability of these ytterbium silicates for EBC applications is also discussed.

• Journal of the Korean institute of surface engineering
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• v.55 no.6
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• pp.376-382
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• 2022

Yb₂Si₂O₇ has a coefficient of thermal expansion similar to that of the base material of SiC and has excellent corrosion resistance in a high-temperature oxidizing atmosphere including water vapor, so it is being studied as one of the materials for environmental barrier coatings (EBCs). In this study, Yb₂Si₂O₇ powder granule is deposited using atmospheric plasma spraying (APS) with different Ar/He ratios. Phase formation and microstructural characteristics are investigated with the coated specimens. In the coating layer, the crystallinity decreased, and the amorphous content increased from an increase in the ratio of Ar. In addition, the various types of particles involved by local volatilization of Si according to the Ar/He ratios were identified.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.4 no.3
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• pp.238-244
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• 1994

We investigated solution growth of silicon on borosilicate and quartz glass substrates in the temperature range of $800^{\circ}C~520^{\circ}C$. A thin Al-Si layer evaporated onto the substrate serves to improve the wetting between the substrate and the Al/Ga solvent. Nucleation takes place by a reaction of Al with $SiO_2$ from the substrate. We obtained silicon deposits with a grain size up to a few 100 $\mu\textrm{m}$. There was a perferential (111) orientation for the case of quartz glass substrates while there is a strong contribution of other orientations for the deposition of Si on borosilicate glass substrates.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2023.05a
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• pp.47-48
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• 2023

In the domestic industrial sector, greenhouse gases emitted from the cement industry account for about 10%, with most of them generated during the cement clinker calcination process. During the calcination process, 57% of carbon dioxide is emitted from the decarbonation reaction of limestone, 30% from fuel consumption, and 13% from electricity usage. In response to these issues, the cement industry is making efforts to reduce carbon dioxide emissions by developing technologies for raw material substitution and conversion, improving process efficiency by utilizing low-carbon alternative heat sources, developing CO₂ capture and utilization technologies, and recycling waste materials. In addition, due to the limitations in purchasing and storing industrial byproducts generated from industrial facilities, many studies are underway regarding the recycling of construction waste. Therefore, this study analyzes the manufacture of calcium silicate cement (CSC), which can store carbon dioxide as carbonate minerals in industrial facilities, and aims to contribute to the development of environmentally friendly regenerated cement using construction waste.

• Journal of the Korean institute of surface engineering
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• v.56 no.6
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• pp.443-450
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• 2023

SiC/SiC_f CMC is vulnerable to water vapor corrosion at a high temperature of 1500℃. So, EBC (Environmental Barrier Coating) materials are required to protect Si-based CMCs. Ytterbium silicates are reported to have coefficient of thermal expansion (CTE) similar to that of the base material, such as SiC/SiC_f CMC. When the EBC are materials exposed to high temperature environment, the interface between ytterbium silicates and SiC/SiC_f CMC is not separated, and the coating purpose can be safely achieved. For the perspective of EBC applications, thermally grown oxide (TGO) layer with different CTE is formed by the reaction with water vapor in EBC, which leads to a decrease in life time. In this study, we prepare two types of ytterbium silicates to observe the corrosion behavior during the expose to high temperature and water vapor. In order to observe this behavior, the steam-jet furnace is prepared. In addition, phase formation of these ytterbium silicates is analyzed with microstructures by the before/after steam-jet evaluation at 1500℃ for 100 h.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.28 no.5
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• pp.295-299
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• 2015

In this paper to improve the ionic conduction properties, lanthanum silicate apatite $La_{9.33}(SiO_4)_6O_2$ ceramic, which substituted by V ions at Si-site, were fabricated by the mixed-oxide method. And we investigated the structural and electrical properties of $La_{9.33}(Si_{6-x}V_x)O_{26}$ specimens with variation of dopants for the application of solid oxide fuel cells. The sintering temperature of $La_{9.33}(Si_{6-x}V_x)O_{26}$ specimens decreased from $1,600^{\circ}C$ to $1,400^{\circ}C$. As results of X-ray diffraction patterns, all $La_{9.33}(Si_{6-x}V_x)O_{26}$ specimens showed the formation of a complete solid solution in a apatite polycrystallin structure. But the specimens doped with more than 1.5mol% showed the second phase, $La_2SiO_5$ and $SiO_2$. The specimen dopants with 1.0 mol% showed the maximum ion conductivity. Ion conducting and activation energy of the $La_{9.33}(Si_5V_1)O_26$ specimens were about $7.8{\times}10^{-4}S/cm$ 1.62 eV at $600^{\circ}C$, respectively.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.1 no.1
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• pp.92-99
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• 1991

The reaction obtaining $SiO_2$ fine particle from $ Si(OC_2H_5)_4$consists of two steps, that is, hydrolysis and polycondensation. Polycondensation is the first order with respect to the concentration of $Si(OC_2H_5)_4$As the concentration of water, ammonia reaction temperature are increased, the reaction rate constant of polycondensation is increased.Silica particles formed are spherical and very uniformly dispersed. The diameters of them are be-tween 0.06 and $0.27\mu\textrm{m}$. As the initial concentration of $Si(OC_2H_5)_4$is decreased and the reaction temper-ature is increased, the diameters of silica particles are reduced. The rate of particles growth derived from time vs, conversion data, is represented as follows; d=a.ln(Xa)+b, where d is the diameter of silica and a, b are constant. The final diameter of silica approaches to the value of b.