• Proceedings of the Korean Vacuum Society Conference
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• 2013.08a
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• pp.173-173
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• 2013

최근에 고효율의 형광체를 개발하고자 무기물 모체에 주입된 희토류 이온의 발광에 대한 연구가 급부상하고 있다. 형광체는 고휘도, 넓은 시청 각도와 저 비용으로 인하여 대형 평판 디스플레이 분야로 그 응용성을 확장하는 플라즈마 디스플레이 패널 제작에 있어서 매우 중요한 물질이다. 현재 적색 형광체로 널리 사용되고 있는 발광 물질은 YBO3:Eu3+ 혹은 (Y,Gd)BO3:Eu3+ 형광체이지만, Eu3+ 이온이 중심대칭의 자리에 위치하기 때문에, Eu3+ 이온의 5D07F1 전이에 의한 주황색의 발광 세기가 5D07F2 전이에 의한 적색의 세기보다 강하여 고품질의 색상을 구현하는데 상당한 어려움이 있다. 이러한 문제점을 해결하기 위하여 새로운 모체 격자를 갖는 적색, 녹색, 청색 형광체 개발에 많은 노력이 집중되고 있다. 본 연구에서는 형광체 합성시 중요한 변수의 하나인 소결 온도가 새로운 다양한 색을 방출하는 형광체 분말 CaSiO4:RE3+ (RE=Eu, Sm, Tb, Dy, Ce)의 특성에 미치는 영향을 조사하였다. CaSiO4:RE3+ (RE=Eu, Sm, Tb, Dy, Ce) 형광체 분말 시료는 초기 물질 CaO (99.99%), SiO2 (99.99%), Eu2O3 (99.99%), Sm2O3 (99.9%), Tb4O7 (99.9%), Dy2O3 (99.9%), CeO2 (99.9%)을 화학적량으로 준비하였다. 볼밀, 건조 작업을 한 후에, 시료를 막자사발에 넣고 분쇄하여 3시간의 하소 공정과 5시간의 소결 공정을 수행하였다. 이때 소결 온도를 변수로 선택하여 각각 $800^{\circ}C$, $900^{\circ}C$, $1,000^{\circ}C$, $1,100^{\circ}C$에서 소결 작업을 수행하여 합성 분말의 구조, 표면, 광학적 특성을 측정하여 소결 온도가 미치는 영향을 조사하였다. Eu3+가 도핑된 CaSiO4 형광체 분말의 경우에, 발광 스펙트럼은 597, 618, 655, 707 nm에서 관측되었으며, 소결 온도가 $800^{\circ}C$에서 $1,100^{\circ}C$로 증가함에 따라 모든 발광 스펙트럼의 세기는 순차적으로 증가함을 나타내었다. Tb3+가 도핑된 CaSiO4 형광체 분말의 경우에 관측된 발광 스펙트럼은 주 피크인 549 nm를 중심으로 하여 세기가 상대적으로 작은 493, 592, 626 nm의 피크들이 관측되었으며, 소결 온도가 증가함에 따라 전반적으로 발광 세기들이 증가하는 경향을 나타내었다. Sm3+가 도핑된 CaSiO4 형광체의 경우에, 발광 스펙트럼은 전형적인 Sm3+이온에 의한 전이 신호들이 605, 570, 653 nm에서 나타났다. 발광 스펙트럼의 세기는 소결 온도에 비례하여 증가하였다. Ce3+가 도핑된 경우에 발광 스펙트럼은 소결 온도에 관계없이 401 nm에서 관측되었으며, 소결 온도에 따라 발광 세기의 변화가 나타났다. 이 실험 결과로 부터, 합성시 적절한 소결 온도의 선택이 고발광 효율의 형광체를 제작하는데 있어서 매우 중요한 요소가 됨을 확인할 수 있었다.

• Korean Journal of Materials Research
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• v.2 no.5
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• pp.330-336
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• 1992

Four distinctive hot pressed and heat treated S${i_3}{N_4}$ceramics, S${i_3}{N_4}$-8%${Y_2}{O_3}$, S${i_3}{N_4}$-6% ${Y_2}{O_3}$-2% $A{l_2}{O_3}$, S${i_3}{N_4}$-4% ${Y_2}{O_3}$-3% $A{l_2}{O_3}$, 그리고 S${i_3}{N_4}$-1% MgO-1% Si$O_2$(in wt%), were prepared and characterized by X-ray diffraction, scanning electron microscopy, image analysis and mechanical tests. The fracture toughness of S${i_3}{N_4}$-8% ${Y_2}{O_3}$specimens containing large elongated grains showed the highest value of about 9.8MPa$m^{1/2}$. Two out of four S${i_3}{N_4}$, ceramics(S${i_3}{N_4}$-6% ${Y_2}{O_3}$-2% $A{l_2}{O_3}$and S${i_3}{N_4}$-4% ${Y_2}{O_3}$-3% $A{l_2}{O_3}$) heat treated at 200 $0^{\circ}C$retained the fracture strength of over 900MPa and fracture toughness of over 8.0MPa$m^{1/2}$. Large ${\beta}$-S${i_3}{N_4}$grains having a diameter larger than 1${\mu}$m appeared to contribute to increase in fracture toughness.

• Journal of the Korean Recycled Construction Resources Institute
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• v.7 no.1
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• pp.22-28
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• 2019

Cement is a basic material for the construction industry and it requires high temperature sintering when manufacturing cement. $CO_2$ emissions from raw materials and fuels are recognized as new environmental problems and efforts are underway to reduce them. Techniques for reducing $CO_2$ in concrete are also recommended to use blended cement such as blast furnace slag or fly ash. In addition, the construction waste generated in the dismantling of concrete structures is recognized as another environmental problem. Thus, various methods are being implemented to increase the recycling rate. The purpose of this study is to utilize the inorganic raw materials generated during the dismantling of the structure as a raw material for the low carbon type cement binder. Such as, waste concrete powder, waste cement block, waste clay brick and waste textile as raw materials for low carbon type cement binder. From the research results, low carbon type cement binder was manufactured from the raw material composition of waste concrete powder, waste cement block, waste clay brick and waste textile.

• Korean Journal of Optics and Photonics
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• v.33 no.5
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• pp.218-229
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• 2022

We have investigated reliable inspection methods for finding the defects generated during the manufacturing process of lightweight, large-aperture satellite telescope mirrors using silicon carbide, and we have measured the basic physical properties of the mirrors. We applied the advanced ceramic material (ACM) method, a combined method using liquid-silicon penetration sintering and chemical vapor deposition for the carbon molded body, to manufacture four SiC mirrors of different sizes and shapes. We have provided the defect standards for the reflectors systematically by classifying the defects according to the size and shape of the mirrors, and have suggested effective nondestructive methods for mirror surface inspection and internal defect detection. In addition, we have analyzed the measurements of 14 physical parameters (including density, modulus of elasticity, specific heat, and heat-transfer coefficient) that are required to design the mirrors and to predict the mechanical and thermal stability of the final products. In particular, we have studied the detailed measurement methods and results for the elastic modulus, thermal expansion coefficient, and flexural strength to improve the reliability of mechanical property tests.

• Korean Chemical Engineering Research
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• v.60 no.3
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• pp.459-467
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• 2022

Redispersion of Pt-Sn particles in Pt, PtSn catalyst which have been sintered by high temperature hydrogen reduction was investigated using oxygen treatment with various temperatures. The aim of this study was to understand the relationship between the catalytic activity for propane dehydrogenation reaction and the change in the physicochemical properties of the catalyst. X-ray diffraction analysis (XRD), CO pulse chemisorption, and H₂ temperature programmed reduction (H₂-TPR) were performed to investigate the state of active metal and interactions between particles of redispersed catalyst. It was confirmed that the dispersion and particle size of platinum, the crystal phase of the catalyst, and the reduction behavior were changed according to the oxygen treatment. As for the catalytic activity in propane dehydrogeantion, sintered PtSn catalyst treated with oxygen at 500 ℃ showed best activity and recovery of initial activity. It was confirm that catalyst after oxygen treatment at 500 ℃ showed high dispersion of Pt and decreased particle size as the results of CO pulse chemisorption and XRD of catalyst, and thus the redispersion of PtSn particles in sintered catalyst was occurred. Catalytic activity was recovered due to redispersion using oxygen treatment, and the activity recovery of the PtSn catalyst was higher than that of Pt catalyst.

• Korean Chemical Engineering Research
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• v.60 no.4
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• pp.620-629
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• 2022

By varying various experimental conditions such as heating rate, molar hourly space velocity (MHSV), and nitridation reaction temperature, vanadium oxynitride was prepared through temperature programmed reduction/nitridation reaction (TPRN) of vanadium pentoxide and ammonia, and characterization were performed. In order to investigate the physico-chemical properties of the prepared catalyst, N₂ adsorption-desorption analysis, X-ray diffraction analysis (XRD), hydrogen temperature programmed reduction (H₂-TPR), temperature programmed oxidation (TPO), ammonia temperature programmed desorption (NH₃-TPD), transmission electron microscopy (TEM) was performed. Transformation of V₂O₅ with 5 m² g^-1 low specific surface area by reduction at 340 ℃ to V₂O₃ showed a high specific surface area value of 115 m² g^-1 by micropore formation. As the nitridation temperature increased beyond that, the specific surface area continued to decrease due to sintering. The nitridation reaction variable that had the greatest influence on the specific surface area was the reaction temperature, and the x + y value of VN_xO_y of a single phase approached from 1.5 to 1.0 as the nitridation reaction temperature increased. At a high reaction temperature of 680 ℃, the cubic lattice constant a was VN. close to the value. At 680 ℃, the highest nitridation temperature among the experimental conditions, the ammonia conversion rate was 93%, and no deactivation was observed.

• Journal of the korean academy of Pediatric Dentistry
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• v.34 no.1
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• pp.1-12
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• 2007

The purpose of this study was to evaluate the effect that various concentration and application time of hydrogen peroxide had on tooth whitening and physical properties. The hydroxyapatite (HA) discs of $12mm({\Phi}){\times}1.2mm(t)$ in dimensions were made by compression $(100kg/cm^2)$ and sintering (at $1350^{\circ}C$ for 2 hours) All specimens were polished sequentially with '240 through '2000 emery paper and one side of each specimen was polished finally with $0.3{\mu}m$ alumina paste. The discs were placed in sterile whole stimulated saliva overnight at $37^{\circ}C$ in order to form an in vitro pellicle layer. Then the discs were rinsed with distilled water and soaked into staining broth at $37^{\circ}C$ for 7 days. These stained specimens were bleached with hydrogen peroxide according to the change of concentration $(3{\sim}30%)$ and application time ($3{\sim}10$ days). The specimens were analyzed with a spectrophotometer, X-ray diffractometer (XRD), scanning electron microscope (SEM), surface roughness tester, microhardness tester and biaxial flexural strength. The results of present study can be summarized as follows : 1. The bleaching effect was increased with the increased concentration and the extended application time of hydrogen peroxide. 2. The surface roughness was significantly increased from the specimen bleached with 15% hydrogen peroxide for 10 days and with 30% for 7 and 10 days respectively (p<0.05). 3. The changes of crystal phase observed by XRD between before and after bleaching weren't shown of any difference, but microporous structure of surface observed by SEM was shown of increase with the increased concentration and the extended application. 4. The biaxial flexural strength was significantly decreased from bleaching of specimen with 30% hydrogen peroxide for 7 and 10 days respectively (p<0.05) 5. Microhardness was significantly decreased from bleaching with 15% hydrogen peroxide for 10 days and with 30% for 3, 7 and 10 days respectively (p<0.05). Although the tooth bleaching effect was greater when the high concentration was applied, further in vivo experiment will be needed to prove it's safety.

• Applied Chemistry for Engineering
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• v.10 no.4
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• pp.557-562
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• 1999

The reaction properties of Pd. Pd-Ce and Pd-La catalysts supported on ${\gamma}-Al_2O_3$ were investigated in the oxidation reaction of methane($CH_4$) exhausted from the compressed natural gas vehicle in a U-tube flow reactor with gas hourly space velocity of $72,000h^{-1}$. The catalysts were characterized by X-ray diffraction(XRD), X-ray photoelectron spectroscopy(XPS), BET surface area and hydrogen chemisorption. Pd catalyst prepared by $Pd(NO_3)_2$ as a palladium precursor and calcined at $600^{\circ}C$ showed the highest activity for a methane oxidation. Catalytic activity of calcined $Pd/{\gamma}-Al_2O_3$ in which most of palladium was converted into palladium oxide species was higher than that of reduced $Pd/{\gamma}-Al_2O_3$ in which most of palladium existed in palladium metal by XRD. As increasing the number of reaction cycles in the wide range of redox, the catalytic activity of $Pd/{\gamma}-Al_2O_3$ was decreased and the highly active window became narrower. Lanthanum oxide promoted Pd catalyst, $Pd/La/{\gamma}-Al_2O_3$ showed enhanced thermal stability compared with $Pd/{\gamma}-Al_2O_3$ even after aging at $1000^{\circ}C$, which was ascribed to the role of La as a promoter to suppress the sintering of palladium metal and ${\gamma}-Al_2O_3$ support. Almost all of methane was removed by the reaction with NO at the redox ratio of 1.2 in case of oxygen excluded steam, but that activity was significantly decreased in the steam containing oxygen.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.29 no.6
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• pp.317-328
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• 2019

In this work, we investigated clay and raw materials from China (black clay, red clay, white clay) and Korea (Cheonan clay, Obu clay) used for the manufacture of porcelain products. According to chemical analysis results, feldspar components containing CaO, K₂O, Na₂O and quartz are found in clay materials besides primary clay such as kaollinte, for the clay materials from Korea, which is found more in clay materials from Korea than from China. For the Fe₂O₃ content, governing whiteness of porcelain products, more iron oxide (> 5 %) is found in Korean clays (Cheonan clay, obu clay, red clay) compared to those form China (black, white clay). Through X-ray diffraction analysis, kaolinite and Halloysite are found to be main phases for all the raw materials and second phases such as quartz and pyrophyllite are found. Using these clay materials, raw materials for porcelain products were produced, and the physicochemical properties were investigated for sintered samples. Absorption rate is in order of Baekja-A < Baekja-B < Yeonbuncheong < Jinbuncheong < Cheongja, and the sample, sintered at 1250℃ in reductive atmosphere, exhibits the lowest absorption rate. Comparing the color of the sintered samples, the samples sintered in oxidative atmosphere (L^* value: 86~95 %) show higher whiteness value than those sintered in reductive atmosphere (L^* value: 81~93 %). For the Cheongja and Buncheong, the samples sintered in reductive atmosphre shows higher whiteness, L^* values, and low a^*/b^* value, which is due to reduction of iron oxide (Fe₂O₃).

• Journal of the Mineralogical Society of Korea
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• v.16 no.4
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• pp.307-320
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• 2003

Garnet has been considered as a possible matrix for the immobilization of radioactive actinides. It is expected that Fe­based garnet be able to have the high substitution ability of actinide elements because ionic radius of Fe in tetrahedral site is larger than that of Si of Si­based garnet. Accordingly, we synthesized Fe­garnet with the batch composition of $Ca_{2,5}$C $e_{0.5}$Z $r_2$F $e_3$ $O_{12}$ and $Ca_2$CeZrFeF $e_3$ $O_{12}$ and studied their phase relations and properties. Mixed samples were fabricated in pellet forms under the pressure of 400 kg/$\textrm{cm}^2$ and were sintered in the temperature range of 1100∼140$0^{\circ}C$ in atmospheric conditions. Phase identification and chemical composition of synthesized samples were analyzed by XRD and SEM/EDS. In results, where the compounds were sintered at 130$0^{\circ}C$, we optimally obtained Fe­garnets as the main phase, even though some minor phases like perovskite were included. The compositions of Fe­garnets synthesized from the batch compositions of $Ca_{2,5}$C $e_{0.5}$Z $r_2$F $e_3$ $O_{12}$ and $Ca_2$CeZrFeF $e_3$ $O_{12}$, are $Ca_{2.5­3.2}$C $e_{0.3­0.7}$Z $r_{1.8­2.8}$F $e_{1.9­3.2}$ $O_{12}$ and $Ca_{2.2­2.5}$C $e_{0.8­1.0}$Z $r_{1.3­1.6}$ F $e_{0.4­.07}$ F $e_{3­3.2}$ $O_{12}$, respectively. Ca contents were exceeded and Ce contents were exceeded or depleted in 8­coodinated site, comparing to the initial batch composition. These results were caused by the compensation of the difference of ionic radius between Ca and Ce.