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
제23권 제12호 (2013년 12월) 13건
1.
2013.12
구독 인증기관 무료, 개인회원 유료
We present an easy method of preparing two-dimensional (2D) periodic hollow tin oxide (SnO2) hemisphere array gas sensors using polystyrene (PS) spheres as a template. The structures were fabricated by the sputter deposition of thin tin (Sn) metal over an array of PS spheres on a planar substrate followed by calcination at an elevated temperature to oxidize Sn to SnO2 while removing the PS template cores. The SnO2 hemisphere array structures were examined by scanning electron microscopy and X-ray diffraction. The structures were calcined at various temperatures and their sensing properties were examined with varying operation temperatures and concentrations of nitric oxide (NO) gas. Their gas-sensing properties were investigated by measuring the electrical resistances in air and the target gases. The measurements were conducted at different NO concentrations and substrate temperatures. A minimum detection limit of 30 ppb, showing a sensitivity of S = 1.6, was observed for NO gas at an operation temperature of 150˚C for a sample having an Sn metal layer thickness corresponding to 30 sec sputtering time and calcined at 600˚C for 2 hr in air. We proved that high porosity in a hollow SnO2 hemisphere structure allows easy diffusion of the target gas molecules. The results confirm that a 2D hollow SnO2 hemisphere array structure of micronmeter sizes can be a good structural morphology for high sensitivity gas sensors.
4,000원
2.
2013.12
구독 인증기관 무료, 개인회원 유료
Fe4[Fe(CN)6]3 coated on a mica or TiO2/mica surface as infrared reflective blue pigment was prepared by a hydrothermal method. Fe4[Fe(CN)6]3, used as coloring agent, was uniformly coated on mica or TiO2/mica under the optimized condition of a 1.2 : 1 weight ratio between iron(III) chloride hexahydrate and potassium ferrocyanidetrihydrate at the initial pH level of 4.5 at 70˚C. The infrared (IR)-reflective pigments were characterized by SEM, Zeta-potenial, FT-IR, and UV-VIS NIR spectrophotometry. Especially the CIE color coordinate and total solar reflectance(TSR) properties of the pigments were investigated in relation to variation of the coating and coated substrate thicknesses. Isolation-heat paint was prepared with 20 wt% blue pigments fully dispersed in acryl-urethane resin and several additives to coat the film uniformly. The films were also measured with CIE color coordinate, TSR, and the surface temperature was recorded by an isolation-heat measuring system. The pigments and films of Fe4[Fe(CN)6]3 coated on mica and TiO2/mica showed high TSR values compared with the TSR value of Fe4[Fe(CN)6]3 itself. According to the increase of TSR value, the property of isolation-heat is effective. To realize the optimal blue color, we applied the the pigment to TiO2 coated mica(TM(b)) which has blueish interference color. The pigment of Fe4[Fe(CN)6]3 coated on TM(b) shows a strong blue color compared with that of Fe4[Fe(CN)6]3 coated on TiO2/Mmca(TM(w)), which has a whitish interference color.
4,000원
3.
2013.12
구독 인증기관 무료, 개인회원 유료
Tungsten oxide films were prepared by an electrochemical deposition method for use as the anode in rechargeable lithium batteries. Continuous potentiostatic deposition of the film led to numerous cracks of the deposits while pulsed deposition significantly suppressed crack generation and film delamination. In particular, a crack-free dense tungsten oxide film with a thickness of ca. 210 nm was successfully created by pulsed deposition. The thickness of tungsten oxide was linearly proportional to deposition time. Compositional and structural analyses revealed that the as-prepared deposit was amorphous tungsten oxide and the heat treatment transformed it into crystalline triclinic tungsten oxide. Both the as-prepared and heat-treated samples reacted reversibly with lithium as the anode for rechargeable lithium batteries. Typical peaks for the conversion processes of tungsten oxides were observed in cyclic voltammograms, and the reversibility of the heat-treated sample exceeded that of the as-prepared one. Consistently, the cycling stability of the heat-treated sample proved to be much better than that of the as-prepared one in a galvanostatic charge/discharge experiment. These results demonstrate the feasibility of using electrolytic tungsten oxide films as the anode in rechargeable lithium batteries. However, further works are still needed to make a dense film with higher thickness and improved cycling stability for its practical use.
4,000원
4.
2013.12
구독 인증기관 무료, 개인회원 유료
This study was performed with an aim to improve the early-age strength of concrete containing fly ash, which is known to increase the long-age strength of concrete, reduce drying shrinkage, and enhance water tightness. The composition was partially substituted with calcium sulfoaluminate (CSA), from which ettringite is actively produced, in the early stages of hydration to verify its effect on improving the early-age strength and to determine the optimal mixing ratio. For this purpose, up to 30 % of the cement weight was substituted with fly ash, and the amount of CSA substitution was 8% of the fly ash weight. The mixtures were then fabricated into concrete specimens for compressive strength measurement and analysis of the correlation between the hydration products and the compressive strength.
4,000원
5.
2013.12
구독 인증기관 무료, 개인회원 유료
To understand how reactivity between reinforcing nanoparticles and aqueous solution affects electrodeposited Cu thin films, two types of commercialized cerium oxide (ceria, CeO2) nanoparticles were used with copper sulfate electrolyte to form in-situ nanocomposite films. During this process, we observed variation in colors and pH of the electrolyte depending on the manufacturer. Ceria aqueous solution and nickel sulfate (NiSO4) aqueous solutions were also used for comparison. We checked several parameters which could be key factors contributing to the changes, such as the oxidation number of Cu, chemical impurities of ceria nanoparticles, and so on. Oxidation number was checked by salt formation by chemical reaction between CuSO4 solution and sodium hydroxide (NaOH) solution. We observed that the color changed when H2SO4 was added to the CuSO4 solution. The same effect was obtained when H2SO4 was mixed with ceria solution; the color of ceria solution changed from white to yellow. However, the color of NiSO4 solution did not show any significant changes. We did observe slight changes in the pH of the solutions in this study. We did not obtain firm evidence to explain the changes observed in this study, but changes in the color of the electrolyte might be caused by interaction of Cu ion and the by-product of ceria. The mechanical properties of the films were examined by nanoindentation, and reaction between ceria and electrolyte presumably affect the mechanical properties of electrodeposited copper films. We also examined their crystal structures and optical properties by X-ray diffraction (XRD) and UV-Vis spectroscopy.
4,000원
6.
2013.12
구독 인증기관 무료, 개인회원 유료
High-quality β-silicon carbide (SiC) coatings are expected to prevent the oxidation degradation of carbon fibers in carbon fiber/silicon carbide (C/SiC) composites at high temperature. Uniform and dense β-SiC coatings were deposited on carbon fibers by low-pressure chemical vapor deposition (LP-CVD) using silane (SiH4) and acetylene (C2H2) as source gases which were carried by hydrogen gas. SiC coating layers with nanometer scale microstructures were obtained by optimization of the processing parameters considering deposition mechanisms. The thickness and morphology of β-SiC coatings can be controlled by adjustment of the amount of source gas flow, the mean velocity of the gas flow, and deposition time. XRD and FE-SEM analyses showed that dense and crack-free β-SiC coating layers are crystallized in β-SiC structure with a thickness of around 2 micrometers depending on the processing parameters. The fine and dense microstructures with micrometer level thickness of the SiC coating layers are anticipated to effectively protect carbon fibers against the oxidation at high-temperatures.
4,000원
7.
2013.12
구독 인증기관 무료, 개인회원 유료
Graphene oxide has been synthesized by microwave-assisted exfoliation of graphite oxide prepared by modified Hummers method. Graphite was oxidized in a solution of H2O2 and KMnO4 at 65~80˚C, followed by 10 % H2O2 solution treatment at 80~90˚C. The graphite oxide was exfoliated under microwave irradiation of 1 kW and was reduced to graphene effectively by hydrazine hydrate (H4N2·H2O) treatment. The exfoliation of graphene oxide was significantly affected by the microwave irradiation on (heating)/off (cooling) period. An on/off period of 10 s/20 s resulted in much more effective exfoliation than that of 5 s/10 s with the same total treatment time of 10 min. This can be explained by the higher exfoliation temperature of 10 s/20 s. Repetition of the graphite oxidation and exfoliation processes also enhanced the exfoliation of graphene oxide. The thickness of the final graphene products was estimated to be several layers. The D band peaks of the Raman spectra of the final graphene products were quite low, suggesting a high crystal quality.
4,000원
8.
2013.12
구독 인증기관 무료, 개인회원 유료
A stoichiometric mixture of evaporating materials for ZnAl2Se4 single-crystal thin films was prepared in a horizontalelectric furnace. These ZnAl2Se4 polycrystals had a defect chalcopyrite structure, and its lattice constants were a0=5.5563Åand c0=10.8897Å.To obtain a single-crystal thin film, mixed ZnAl2Se4 crystal was deposited on the thoroughly etched semi-insulating GaAs(100) substrate by a hot wall epitaxy (HWE) system. The source and the substrate temperatures were 620oCand 400oC, respectively. The crystalline structure of the single-crystal thin film was investigated by using a double crystal X-ray rocking curve and X-ray diffraction ω-2θ scans. The carrier density and mobility of the ZnAl2Se4 single-crystal thin filmwere 8.23×1016cm−3 and 287m2/vs at 293K, respectively. To identify the band gap energy, the optical absorption spectra ofthe ZnAl2Se4 single-crystal thin film was investigated in the temperature region of 10-293K. The temperature dependence ofthe direct optical energy gap is well presented by Varshni's relation: Eg(T)=Eg(0)−(αT2/T+β). The constants of Varshni'sequation had the values of Eg(0)=3.5269eV, α=2.03×10−3eV/K and β=501.9K for the ZnAl2Se4 single-crystal thin film.The crystal field and the spin-orbit splitting energies for the valence band of the ZnAl2Se4 were estimated to be 109.5meVand 124.6meV, respectively, by means of the photocurrent spectra and the Hopfield quasicubic model. These results indicatethat splitting of the ∆so definitely exists in the Γ5 states of the valence band of the ZnAl2Se4/GaAs epilayer. The threephotocurrent peaks observed at 10K are ascribed to the A1-, B1-exciton for n=1 and C21-exciton peaks for n=21.
4,000원
9.
2013.12
구독 인증기관 무료, 개인회원 유료
Freeze drying of a porous Cu-Sn alloy with unidirectionally aligned pore channels was accomplished by using a composite powder of CuO-SnO2 and camphene. Camphene slurries with CuO-SnO2 content of 3, 5 and 10 vol% were prepared by mixing with a small amount of dispersant at 50˚C. Freezing of a slurry was done at -25˚C while the growth direction of the camphene was unidirectionally controlled. Pores were generated subsequently by sublimation of the camphene during drying in air for 48 h. The green bodies were hydrogen-reduced at 650˚C and then were sintered at 650˚C and 750˚C for 1 h. XRD analysis revealed that the CuO-SnO2 powder was completely converted to Cu-Sn alloy without any reaction phases. The sintered samples showed large pores with an average size of above 100μm which were aligned parallel to the camphene growth direction. Also, the internal walls of the large pores had relatively small pores. The size of the large pores decreased with increasing CuO-SnO2 content due to the change of the degree of powder rearrangement in the slurry. The size of the small pores decreased with increase of the sintering temperature from 650˚C to 750˚C, while that of the large pores was unchanged. These results suggest that a porous alloy body with aligned large pores can be fabricated by a freeze-drying and hydrogen reduction process using oxide powders.
4,000원
10.
2013.12
구독 인증기관 무료, 개인회원 유료
In this study, green barium strontium silicate phosphor (BaSrSiO4:Eu3+, Eu2+) was synthesized using a solid-statereaction method in air and reducing atmosphere. Investigation of the firing temperature indicates that a single phase of BaSrSiO4is formed when the firing temperature is higher than 1400oC. The effect of firing temperature and doping concentration onluminescent properties are investigated. The light-emitting property was the best when the molar content of Eu2O3 was 0.025mol. Also, the luminescent brightness of the BaSrSiO4 fluorescent substance was the best when the particle size of the bariumwas 0.5µm. BaSrSiO4 phosphors exhibit the typical green luminescent properties of Eu3+ and Eu2+. The characteristics of thesynthesized BaSrSiO4:Eu3+, Eu2+ phosphor were investigated using X-ray diffraction (XRD) and scanning electron microscopy.The maximum emission band of the BaSrSiO4:Eu3+, Eu2+ was 520nm.
4,000원
11.
2013.12
구독 인증기관 무료, 개인회원 유료
AlN epilayers were grown on a c-plane sapphire substrate using hydride vapor phase epitaxy (HVPE). A series of AlN epilayers were grown at 1120˚C with V/III ratios 1.5, 2.5 and 3.5, and the influence of V/III ratio on their properties was investigated. As the V/III ratio was increased, the surface roughness (RMS roughness), Raman shift of E2 high peaks and full-width at half-maximum (FWHM) of symmetrical (002) & asymmetrical (102) of the AlN epilayers increased. However, the intensities of the Raman E2 high peaks were reduced. This indicates that the crystal quality of the grown AlN epilayers was degraded by activation of the parasitic reaction as the V/III ratio was increased. Smooth surface, stress free and high crystal quality AlN epilayers were obtained at the V/III ratio of 1.5. The crystal quality of AlNepilayers is worsened by the promotion of three-dimensional (3D) growth mode when the flow of NH3 is high.
4,000원
12.
2013.12
구독 인증기관 무료, 개인회원 유료
We demonstrated size control of Au nanoparticles by heat treatment and their use as a catalyst for single-walled carbon nanotube (SWNTs) growth with narrow size distribution. We used uniformly sized Au nanoparticles from commercial Au colloid, and intentionally decreased their size through heat treatment at 800 oC under atmospheric Ar ambient. ST-cut quartz wafers were used as growth substrates to achieve parallel alignment of the SWNTs and to investigate the size relationship between Au nanoparticles and SWNTs. After the SWNTs were grown via chemical vapor deposition using methane gas, it was found that a high degree of horizontal alignment can be obtained when the particle density is low enough to produce individual SWNTs. The diameter of the Au nanoparticles gradually decreased from 3.8 to 2.9 nm, and the mean diameter of the SWNTs also changed from 1.6 to 1.2 nm for without and 60 min heat treatment, respectively. Raman results reconfirmed that the prolonged heat treatment of nanoparticles yields thinner tubes with narrower size distribution. This work demonstrated that heat treatment can be a straightforward and reliable method to control the size of catalytic nanoparticles and SWNT diameter.
4,000원
13.
2013.12
구독 인증기관 무료, 개인회원 유료
Recent rapid development of the Chinese economy based on science and technology is challenging Korean industries and economy. Since the driving force for this rapid development of China is known to be scientific technologies, the purpose of this research is to confirm the current status of Chinese scientific research in the field of "Materials Science and Engineering" and propose a strategy for competition with China. Even though there are numerous journals of "Materials Science and Engineering", the 10 most popular journals with high impact factors were selected to cover general materials, nano materials, bio materials, and electronic materials. It was found that the number of scientific papers written by Chinese scientists for the materials field in the 10 journals was slowly increasing from the year 2000 until 2005, but has been rapidly increasing since 2005. This research found that Chinese research activities in the traditional metallic materials and nano materials have tremendously increased to occupy around 30 % or more papers published in several major journals related with materials science and engineering. On the other hand, bio materials and electronic materials research has not been pursued so actively; however, very recently the number of publications in these fields is also beginning to increase. To compete with this tremendously growing Chinese scientific development, Korea should have a policy of "selection and concentration" in materials-related fields, including basic science in nano, bio, and electronic materials.
4,300원
