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
제29권 제2호 (2019년 2월) 10건
1.
2019.02
구독 인증기관 무료, 개인회원 유료
Dual porous structures are observed for the first time on a metallic Cu surface underneath anodic Cu oxide by the application of an anodizing voltage to Cu in oxalic acid. The as-prepared porous Cu surface contains macropores of less than 1 μm diameter and mesopores of about tens of nanometers diameter with circular shapes. The size and density (number of pores/area) of the macropores are dependent on the applied voltage. It is likely that the localized dissolution (corrosion) of Cu in oxalic acid under the anodizing voltages is responsible for the formation of the mesopores, and the combination of a number of the mesopores might create the macropores, especially under a relatively high anodizing voltages or a prolonged anodizing time. The variations of pore structure (especailly macropores) with applied voltage and time are reasonably explained on the basis of the proposed mechanism of pore formation.
4,000원
2.
2019.02
구독 인증기관 무료, 개인회원 유료
Lead free (Ba0.7Ca0.3) TiO3 thick films with nano-sized grains are prepared using an aerosol deposition (AD) method at room temperature. The crystallinity of the AD thick films is enhanced by a post annealing process. Contrary to the sharp phase transition of bulk ceramics that has been reported, AD films show broad phase transition behaviors due to the nanosized grains. The polarization-electric hysteresis loop of annealed AD film shows ferroelectric behaviors. With an increase in annealing temperature, the saturation polarization increases because of an increase in crystallinity. However, the remnant polarization and cohesive field are not affected by the annealing temperature. BCT AD thick films annealed at 700 ℃/2h have an energy density of 1.84 J/cm3 and a charge-discharge efficiency of 69.9%, which is much higher than those of bulk ceramic with the same composition. The higher energy storage properties are likely due to the increase in the breakdown field from a large number of grain boundaries of nano-sized grains.
4,000원
3.
2019.02
구독 인증기관 무료, 개인회원 유료
A heterogeneous photocatalytic system is attracting much interest for water and air purification because of its reusability and economical advantage. Electrospun nanofibers are also receiving immense attention for efficient photocatalysts due to their ultra-high specific surface areas and aspect ratios. In this study, ZnO nanofibers with average diameters of 71, 151 and 168 nm are successfully synthesized by facile electrospinning and a subsequent calcination process at 500 ℃ for 3 h. Their crystal structures, morphology features and optical properties are systematically characterized by X-ray diffraction, scanning electron microscopy, UV-Vis and photoluminescence spectroscopies. The photocatalytic activities of the ZnO nanofibers are evaluated by the photodegradation of a rhodamine B aqueous solution. The results reveal that the diameter of the nanofiber, controlled by changing the polymer content in the precursor solution, plays an important role in the photocatalytic activities of the synthesized ZnO nanofibers.
4,000원
4.
2019.02
구독 인증기관 무료, 개인회원 유료
We report on stretchable electrochromic films of poly(3-hexylthiophene) (P3HT) fabricated on silver nanowire (AgNW) electrodes. AgNWs electrodes are prepared on polydimethylsiloxane (PDMS) substrates using a spray coater for stretchable electrochromic applications. On top of the AgNW electrode, poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) is introduced to ensure a stable resistance over the electrode under broad strain range by effectively suppressing the protrusion of AgNWs from PDMS. This bilayer electrode exhibits a high performance as a stretchable substrate in terms of sheet resistance increment by a factor of 1.6, tensile strain change to 40%, and stretching cycles to 100 cycles. Furthermore, P3HT film spin-coated on the bilayer electrode shows a stable electrochromic coloration within an applied voltage, with a color contrast of 28.6%, response time of 4-5 sec, and a coloration efficiency of 91.0 cm2/C. These findings indicate that AgNWs/PEDOT:PSS bilayer on PDMS substrate electrode is highly suitable for transparent and stretchable electrochromic devices.
4,000원
5.
2019.02
구독 인증기관 무료, 개인회원 유료
Transition metal oxide is widely used as a water electrolysis catalyst to substitute for a noble metal catalyst such as IrO2 and RuO2. In this study, the sol-gel method is used to synthesize the CuxCo3-xO4 catalyst for the oxygen evolution reaction (OER),. The CuxCo3-xO4 is synthesized at various calcination temperatures from 250 ℃ to 400 ℃ for 4 h. The CuxCo3- xO4 synthesized at 300 ℃ has a perfect spinel structure without residues of the precursor and secondary phases, such as CuO. The particle size of CuxCo3-xO4 increases with an increase in calcination temperature. Amongst all the samples studied, CuxCo3- xO4, which is synthesized at 300?, has the highest activity for the OER. Its onset potential for the OER is 370 mV and the overpotential at 10 mA/cm2 is 438 mV. The tafel slope of CuxCo3-xO4 synthesized at 300 ℃ has a low value of 58 mV/dec. These results are mainly explained by the increase in the available active surface area of the CuxCo3-xO4 catalyst.
4,000원
6.
2019.02
구독 인증기관 무료, 개인회원 유료
In the current steel structures of high-rise buildings, high heat input welding techniques are used to improve productivity in the construction industry. Under the high heat input welding, however, the microstructures of the weld metal (WM) and heat-affected zone (HAZ) coarsen, resulting in the deterioration of impact toughness. This study focuses mainly on the effects of fine TiN precipitates dispersed in steel plates and B addition in welding materials on grain refinement of the HAZ microstructure under submerged arc welding (SAW) with a high heat input of 200 kJ/cm. The study reveals that, different from that in conventional steel, the γ grain coarsening is notably retarded in the coarse grain HAZ (CGHAZ) of a newly developed steel with TiN precipitates below 70 nm in size even under the high heat input welding, and the refinement of HAZ microstructure is confirmed to have improved impact toughness. Furthermore, energy dispersive spectroscopy (EDS) and secondary-ion mass spectrometry (SIMS) analyses demonstrate that B is was identified at the interface of TiN in CGHAZ. It is likely that B atoms in the WM are diffused to CGHAZ and are segregated at the outer part of undissolved TiN, which contributes partly to a further grain refinement, and consequently, improved mechanical properties are achieved.
4,000원
7.
2019.02
구독 인증기관 무료, 개인회원 유료
Recently, metal cases are widely used in smart phones for their luxurious color and texture. However, when a metal case is used, electric shock may occur during charging. Chip capacitors of various values are used to prevent the electric shock. However, chip capacitors are vulnerable to electrostatic discharge(ESD) generated by the human body, which often causes insulation breakdown during use. This breakdown can be eliminated with a high-voltage chip varistor over 340V, but when the varistor voltage is high, the capacitance is limited to about 2pF. If a chip capacitor with a high dielectric constant and a chip varistor with a high voltage can be combined, it is possible to obtain a new device capable of coping with electric shock and ESD with various capacitive values. Usually, varistors and capacitors differ in composition, which causes different shrinkage during co-firing, and therefore camber, internal crack, delamination and separation may occur after sintering. In addition, varistor characteristics may not be realized due to the diffusion of unwanted elements into the varistor during firing. Various elements are added to control shrinkage. In addition, a buffer layer is inserted in the middle of the varistor-capacitor junction to prevent diffusion during firing, thereby developing a co-fired product with desirable characteristics.
4,000원
8.
2019.02
구독 인증기관 무료, 개인회원 유료
We prepared Y3Al5O12;Ce3+,Pr3+ transparent ceramic phosphor using a solid state reaction method. By XRD pattern analysis and SEM measurement, our phosphors reveal an Ia-3d(230) space group of cubic structure, and the transparent ceramic phosphor has a polycrystal state with some internal cracks and pores. In the Raman scattering measurement with an increasing temperature, lattice vibrations of the transparent ceramic phosphor decrease due to its more perfect crystal structure and symmetry. Thus, low phonon generation is possible at high temperature. Optical properties of the transparent ceramic phosphor have broader excitation spectra due to a large internal reflection. There is a wide emission band from the green to yellow region, and the red color emission between 610 nm and 640 nm is also observed. The red-yellow phosphor optical characteristics enable a high Color Rendering Index (CRI) in combination with blue emitting LED or LD. Due to its good thermal properties of low phonon generation at high temperature and a wide emission range for high CRI characteristics, the transparent ceramic phosphor is shown to be a good candidate for high power solid state white lighting.
4,000원
9.
2019.02
구독 인증기관 무료, 개인회원 유료
Supercapacitors are attracting much attention in sensor, military and space applications due to their excellent thermal stability and non-explosion. The ionic liquid is more thermally stable than other electrolytes and can be used as a high temperature electrolyte, but it is not easy to realize a high temperature energy device because the separator shrinks at high temperature. Here, we report a study on electrochemical supercapacitors using a composite electrolyte film that does not require a separator. The composite electrolyte is composed of thermoplastic polyurethane, ionic liquid and fumed silica nanoparticles, and it acts as a separator as well as an electrolyte. The silica nanoparticles at the optimum mass concentration of 4wt% increase the ionic conductivity of the composite electrolyte and shows a low interfacial resistance. The 5 wt% polyurethane in the composite electrolyte exhibits excellent electrochemical properties. At 175 ℃, the capacitance of the supercapacitor using our free standing composite electrolyte is 220 F/g, which is 25 times higher than that at room temperature. This study has many potential applications in the electrolyte of next generation energy storage devices.
4,000원
10.
2019.02
구독 인증기관 무료, 개인회원 유료
A powder mixture of 70 wt% Al2O3 and 30 wt% hydroxyapatite (HA) is sintered at 1300 ℃ or 1350 ℃ for 2 h at normal pressure. An MgF2-added composition to make HA into fluorapatite (FA) is also prepared for comparison. The samples without MgF2 show α & β-tricalcium phosphates (TCPs) and Al2O3 phases with no HA at either of the sintering temperatures. In the case of 1,350 ℃, a CaAl4O7 phase is also found. Densification values are 69 and 78 %, and strengths are 156 and 104MPa for 1,300 and 1,350 ℃, respectively. Because the decomposition of HA produces a H2O vapor, fewer large pores of 5-6 μm form at 1,300 ℃. The MgF2-added samples show FA and Al2O3 phases with no TCP. Densification values are 79 and 87%, and strengths are 104 and 143 MPa for 1,300 and 1,350 ℃, respectively. No large pores are observed, and the grain size of FA (1-2 μm) is bigger than that of TCP (0.7 μm ≥) in the samples without MgF2. The resulting TCP/Al2O3 and FA/Al2O3 composites fabricated in situ exhibit strengths 6-10 times higher than monolithic TCP and HA.
4,000원
