간행물
한국재료학회지 KCI 등재 SCOPUS Korean Journal of Materials Research
- 발행기관 한국재료학회
- 자료유형 학술지
- 간기 월간
- ISSN 2799-8525 (Print)2799-8681 (Online)
- 수록기간 1991 ~ 2024
- 주제분류 공학 > 재료공학 공학 분류의 다른 간행물
- 십진분류KDC 530DDC 620
권호리스트/논문검색
제22권 제5호 (2012년 5월) 8건
1.
2012.05
구독 인증기관 무료, 개인회원 유료
Red phosphors Ca1-1.5xWO4:Eux3+ were synthesized with different concentrations of Eu3+ ions by using a solid-statereaction method. The crystal structure of the red phosphors was found to be a tetragonal system. X-ray diffraction (XRD) resultsshowed the (112) main diffraction peak centered at 2θ=28.71o, and the size of crystalline particles exhibited an overalldecreasing tendency according to the concentration of Eu3+ ions. The excitation spectra of all the phosphors were composedof a broad band centered at 275nm in the range of 230-310nm due to O2−→W6+ and a narrow band having a peak at 307nmcaused by O2−→Eu3+. Also, the excitation spectrum presents several strong lines in the range of 305-420nm, which areassigned to the 4f-4f transitions of the Eu3+ ion. In the case of the emission spectrum, all the phosphor powders, irrespectiveof Eu3+ ion concentration, indicated an orange emission peak at 594nm and a strong red emission spectrum centered at 615nm,with two weak lines at 648 and 700nm. The highest red emission intensity occurred at x=0.10mol of Eu3+ ion concentrationwith an asymmetry ratio of 12.5. Especially, the presence of Eu3+ in the Ca1-1.5xWO4:Eux3+ shows very effective use of excitationenergy in the range of 305-420nm, and finally yields a strong emission of red light.
4,000원
2.
2012.05
구독 인증기관 무료, 개인회원 유료
Pure zirconia and x mol% calcia partially stabilized zirconia (x = 1.5, 3, and 8) nanopowders were synthesized by hydrothermal method with various reaction temperatures for 24 hrs. The precipitated precursor of pure zirconia and x mol% calcia doped zirconia was prepared by adding NH4OH to starting solutions; resulting sample was then put into an autoclave reactor. The optimal experimental conditions, such as reaction temperatures and times and amounts of stabilizer CaO, were carefully studied. The synthesized ZrO2 and x mol% CaO-ZrO2 (x = 1.5, 3, and 8) powders were characterized by XRD, SEM, TG-DTA, and Raman spectroscopy. When the hydrothermal temperature was as low as 160˚C, pure ZrO2 and x mol% CaO-ZrO2 (x = 1.5 and 3) powders were identified as a mixture of monoclinic and tetragonal phases. However, a stable tetragonal phase of zirconia was observed in the 8 mol% calcia doped zirconia nanopowder at hydrothermal temperature above 160˚C. To observe the phase transition, the 3 mol% CaO-ZrO2 and 8 mol% CaO-ZrO2 nanopowders were heat treated from 600 to 1000˚C for 2h. The 3 mol% CaO-ZrO2 heat treated at above 1000˚C was found to undergo a complete phase transition from mixture phase to monoclinic phase. However, the 8 mol% calcia doped zirconia appeared in the stable tetragonal phase after heat treatment. The result of this study therefore should be considered as the preparation of 8 mol% CaO-ZrO2 nanopowders via the hydrothermal method.
4,000원
3.
2012.05
구독 인증기관 무료, 개인회원 유료
Ionomer is a thermoplastic that is composed of covalent bonds and ionic bonds. It is possible to use this material in processes such as injection molding or extrusion molding due to the material's high oil resistance, weatherproof characteristics, and shock resistance. In this study, a new ionomer having a multifunctional group was prepared by a stepwise neutralization system with the addition of acidic and salt additives. In step I, to increase the contents of the multifunctional group and the acid degree in ethylene acrylic acid (EAA), MGA was added to the ionomer resin (EAA). A new ionomer was prepared via the traditional preparation method of the ionic cross-linking process. In step II, metal salt was added to the mixture of EAA and MGA. The extrusion process was performed using a twin extruder (L/D = 40, size : Φ30). Ionomer film was prepared for evaluation of gas permeability by using the compression molding process. The degree of neutralized and ionic cross-linked new ionomer was confirmed by FT-IR and XRD analysis. In order to estimate the neutralization of the new ionomer film, various properties such as gas permeation and mechanical properties were measured. The physical strength and anti-scratch property of the new ionomer were improved with increase of the neutralization degree. The gas barrier property of the new ionomer was improved through the introduction of an ionic site. Also, the ionic degree of cross-linking and gas barrier property of the ionomer membrane prepared by stepwise neutralization were increased.
4,000원
4.
2012.05
구독 인증기관 무료, 개인회원 유료
We report on the NO gas sensing properties of Al-doped zinc oxide-carbon nanotube (ZnO-CNT) wire-like layered composites fabricated by coaxially coating Al-doped ZnO thin films on randomly oriented single-walled carbon nanotubes. We were able to wrap thin ZnO layers around the CNTs using the pulsed laser deposition method, forming wire-like nanostructures of ZnO-CNT. Microstructural observations revealed an ultrathin wire-like structure with a diameter of several tens of nm. Gas sensors based on ZnO-CNT wire-like layered composites were found to exhibit a novel sensing capability that originated from the genuine characteristics of the composites. Specifically, it was observed by measured gas sensing characteristics that the gas sensors based on ZnO-CNT layered composites showed a very high sensitivity of above 1,500% for NO gas in dry air at an optimal operating temperature of 200˚C; the sensors also showed a low NO gas detection limit at a sub-ppm level in dry air. The enhanced gas sensing properties of the ZnO-CNT wire-like layered composites are ascribed to a catalytic effect of Al elements on the surface reaction and an increase in the effective surface reaction area of the active ZnO layer due to the coating of CNT templates with a higher surface-to-volume ratio structure. These results suggest that ZnO-CNT composites made of ultrathin Al-doped ZnO layers uniformly coated around carbon nanotubes can be promising materials for use in practical high-performance NO gas sensors.
4,000원
5.
2012.05
구독 인증기관 무료, 개인회원 유료
ZrN nanoparticles were prepared by an exothermic reduction of ZrCl4 with NaN3 in the presence of NaCl flux in a nitrogen atmosphere. Using a solid-state combustion approach, we have demonstrated that the zirconium nitride nanoparticles synthesis process can be completed in only several minutes compared with a few hours for previous synthesis approaches. The chemistry of the combustion process is not complex and is based on a metathesis reaction between ZrCl4 and NaN3. Because of the low melting and boiling points of the raw materials it was possible to synthesize the ZrN phase at low combustion temperatures. It was shown that the combustion temperature and the size of the particles can be readily controlled by tuning the concentration of the NaCl flux. The results show that an increase in the NaCl concentration (from 2 to 13 M) results in a temperature decrease from 1280 to 750˚C. ZrN nanoparticles have a high surface area (50-70 m2/g), narrow pore size distribution, and nano-particle size between 10 and 30 nm. The activation energy, which can be extracted from the experimental combustion temperature data, is: E = 20 kcal/mol. The method reported here is self-sustaining, rapid, and can be scaled up for a large scale production of a transition metal nitride nanoparticle system (TiN, TaN, HfN, etc.) with suitable halide salts and alkali metal azide.
4,000원
6.
2012.05
구독 인증기관 무료, 개인회원 유료
Fe doped TiO2 nanoparticles were prepared under high temperature and pressure conditions by mixture of metal nitrate solution and TiO2 sol. Fe doped TiO2 particles were reacted in the temperature range of 170 to 200˚C for 6 h. The microstructure and phase of the synthesized Fe doped TiO2 nanoparticles were studied by SEM (FE-SEM), TEM, and XRD. Thermal properties of the synthesized Fe doped TiO2 nanoparticles were studied by TG-DTA analysis. TEM and X-ray diffraction pattern shows that the synthesized Fe doped TiO2 nanoparticles were crystalline. The average size and distribution of the synthesized Fe doped TiO2 nanoparticles were about 10 nm and narrow, respectively. The average size of the synthesized Fe doped TiO2 nanoparticles increased as the reaction temperature increased. The overall reduction in weight of Fe doped TiO2 nanoparticles was about 16% up to ~700˚C; water of crystallization was dehydrated at 271˚C. The transition of Fe doped TiO2 nanoparticle phase from anatase to rutile occurred at almost 561˚C. The amount of rutile phase of the synthesized Fe doped TiO2 nanoparticles increased with decreasing Fe concentration. The effects of synthesis parameters, such as the concentration of the starting solution and the reaction temperature, are discussed.
3,000원
7.
2012.05
구독 인증기관 무료, 개인회원 유료
Activated magnetite (Fe3O4-δ) was applied to reducing CO2 gas emissions to avoid greenhouse effects. Wet and dry methods were developed as a CO2 removal process. One of the typical dry methods is CO2 decomposition using activated magnetite (Fe3O4-δ). Generally, Fe3O4-δ is manufactured by reduction of Fe3O4 by H2 gas. This process has an explosion risk. Therefore, a non-explosive process to make Fe3O4-δ was studied using FeC2O4·2H2O and N2. FeSO4·7H2O and (NH4)2C2O4·H2O were used as starting materials. So, α-FeC2O4·2H2O was synthesized by precipitation method. During the calcination process, FeC2O4·2H2O was decomposed to Fe3O4, CO, and CO2. The specific surface area of the activated magnetite varied with the calcination temperature from 15.43 m2/g to 9.32 m2/g. The densities of FeC2O4·2H2O and Fe3O4 were 2.28 g/cm3 and 5.2 g/cm3, respectively. Also, the Fe3O4 was reduced to Fe3O4-δ by CO. From the TGA results in air of the specimen that was calcined at 450˚C for three hours in N2 atmosphere, the δ-value of Fe3O4-δ was estimated. The δ-value of Fe3O4-δ was 0.3170 when the sample was heat treated at 400˚C for 3 hours and 0.6583 when the sample was heat treated at 450˚C for 3 hours. Fe3O4-δ was oxidized to Fe3O4 when Fe3O4-δ was reacted with CO2 because CO2 is decomposed to C and O2.
4,000원
8.
2012.05
구독 인증기관 무료, 개인회원 유료
Chalcogenide-based semiconductors, such as CuInSe2, CuGaSe2, Cu(In,Ga)Se2 (CIGS), and CdTe have attracted considerable interest as efficient materials in thin film solar cells (TFSCs). Currently, CIGS and CdTe TFSCs have demonstrated the highest power conversion efficiency (PCE) of over 11% in module production. However, commercialized CIGS and CdTe TFSCs have some limitations due to the scarcity of In, Ga, and Te and the environmental issues associated with Cd and Se. Recently, kesterite CZTS, which is one of the In- and Ga- free absorber materials, has been attracted considerable attention as a new candidate for use as an absorber material in thin film solar cells. The CZTS-based absorber material has outstanding characteristics such as band gap energy of 1.0 eV to 1.5 eV, high absorption coefficient on the order of 104cm-1, and high theoretical conversion efficiency of 32.2% in thin film solar cells. Despite these promising characteristics, research into CZTS-based thin film solar cells is still incomprehensive and related reports are quite few compared to those for CIGS thin film solar cells, which show high efficiency of over 20%. The recent development of kesterite-based CZTS thin film solar cells is summarized in this work. The new challenges for enhanced performance in CZTS thin films are examined and prospective issues are addressed as well.
4,800원
