Sapphire single crystals have been highlighted for epitaxial of gallium nitride films in high-power laser and light emitting diode industries. Among the many crystal growth methods, vertical Bridgman process is an excellent commercial method for growing high quality sapphire crystals with c-axis. In this study, the thermally induced stress in Sapphire during the vertical Bridgman crystal growth process was investigated using a finite element model. A vertical Bridgman process of 2-inch Sapphire was considered for the model. The effects of vertical and transverse temperature gradients on the thermal stress during the process were discussed based on the finite element analysis results.
Lead zirconate titanate (PZT) thick films with thickness of 10~20 μm were fabricated on silicon substrate by aerosol deposition method. As-deposited films on silicon were annealed at the temperatures of 700 o C. The electrical properties of films deposited by PZT powders were characterized using impedance analyzer and Sawyer-Tower circuit. The PZT powder was prepared by both conventional solid reaction process and sol-gel process. The remanent polarization, coercive field, and dielectric constant of the 10 μm thick film with solid reaction process were 20 μC/cm 2 , 30 kV/cm and 1320, respectively. On the other hand, the PZT films by sol-gel process showed a poor dielectric constant of 635. The reason was probably due to the presence of pores produced from organic residue during annealing.
We have applied mechanical alloying (MA) to produce soft magnetic composite material using a mixture of elemental Fe2O3-Mg powders. An optimal milling and heat treatment conditions to obtain soft magnetic α-Fe/MgO composite with fine microstructure were investigated by X-ray diffraction, differential scanning calorimetry (DSC) and vibrating sample magnetometer (VSM) measurement. It is found that α-Fe/MgO composite powders in which MgO is dispersed in α-Fe matrix are obtained by MA of Fe2O3 with Mg for 30 min. The saturation magnetization of ball-milled powders increases with increasing milling time and reaches to a maximum value of 69.5 emu/g after 5 h MA. The magnetic hardening due to the reduction of the α-Fe grain size by MA was also observed. Densification of the MA powders was performed in a spark plasma sintering (SPS) machine at 800~1000 o C under 60 MPa. X-ray diffraction result shows that the average grain size of α-Fe in α-Fe/MgO nanocomposite sintered at 800 o C is in the range of 110 nm.
Nitrogen oxides (NOX) was emitted from flue gas of stationary sources and exhaust gas of mobile sources, can leads to various environments problems. Selective Catalysts Reduction (SCR) is the most effective NOX removal system.
Commercial V2O5-WO3/TiO2 catalysts, usually containing V2O5 0.5~3 wt%, WO3 5~10 wt%, and V2O5 is active in the reduction of NOX but also in the desired oxidation of SO2 to SO3. To reduce the amount of vanadium, using graphene matrix supported vanadium to synthesize nanocomposite. Then, we fabricated to 1 inch honeycomb type of SCR catalysts adding graphene-vanadium nanocomposite. The chemical-physical characteristics and the catalytic activity were performed by XRD, XRF, BET and Micro-Reactor (MR). As a result, the De-NOX performance was showed, similar to the commercial catalyst activity as 77.8 % and using nanocomposite catalyst as 77.1 % at 350 o C.
Recently the world wide efforts reduce occurrence of CO2; global warming main reason. The aim of this study is to improve recycling rate of the fly ash (FA) and fused waste slag (FWS) from the power plant and to carbonate under supercritical condition (40 o C, 80 kgf/cm 2 pressure, 60 min) for CO2 fixation. Specimens of mortar with various mixing ratios of FA, FWS (from 100:0 to 20:80 in 5 steps of 20 % reduction each time), distilled water and 3 M NaOH alkali activators were prepared. As a result, the proportion of weight change ratio increases with CaO content, to 12 % after carbonation under the supercritical condition. There is difference of compressive strength between the carbonated and the alkali activator mortar specimens. The stabilization of CO2 fixation through carbonation which could confirm the applicability of the eco-friendly materials without loss of compressive strength.
Commercial AR(Alkali Resistant)-glass fiber has a good chemical resistant property, but also has a problem of difficulty in fiberizing process because of high viscosity in melted glass compare with E-glass fiber which is the most widely used for reinforced fiber of composite materials. In this study, we fabricated AR-glass fiber with low zirconia contents compare with commercial AR-glass fiber relatively, and measured properties against E-glass fiber. We obtained transparent clear glass with zirconia contents of 0.5~16 wt% by melting at 1600oC for 2 hours. These AR-glass samples had high visible transmittance of 89~90 %, softening temperature of 703~887oC. And softening temperatures of them were increased according to the increasing zirconia contents. Compare with E-glass, AR-glass contains 4 wt% zirconia has different value of −94oC in softening temperature, +68oC at Log3 temperature and −13oC at Log5 temperature in viscosity.
We could verify good alkali resistant property of the AR-glass fiber with SEM after dipping in alkali solution for 48~72 hours, and also high tensile strength, 1.7 times compare with E-glass fiber at 48 hours and 2.2 times at 72 hours. We conclude that this AR-glass fiber can be widely used as general alkali resistant glass fiber because of easy manufacturing condition and good properties even though it has low zirconia contents.
Y2O3 : Eu 3+ is an excellent red-emitting phosphor, which has been widely used for display devices due to highly luminescent property and chemical stability. In this study, Y2O3 : Eu 3+ red phosphors were prepared using the solid state reaction and RF thermal plasma synthesis. The particle size of Y2O3 : Eu 3+ phosphors obtained by the solid state reaction varied from 10 to 20 μm, and 30~100 nanometer sized Y2O3 : Eu 3+ particles were obtained from a liquid form of raw material through RF thermal plasma synthesis without an additional heat treatment. Photoluminescence measurements of the obtained Y2O3 : Eu 3+ particles showed a red emission peak at 611 nm ( 5 D0→ 7 F2). PL intensity of red nano phosphors prepared by RF thermal plasma synthesis was comparable to that of red phosphors prepared by the solid state reaction, indicating that nano-sized Y2O3 : Eu 3+ red phosphors could be successfully synthesized using one-step process of RF thermal plasma.
Au doped TiO2 nanoparticles have been synthesized using a reverse micelle technique combined with metal alkoxide hydrolysis and condensation. Au doped TiO2 was coated with glass substrate. The size of the particles and thickness of the coating can be controlled by manipulating the relative rates of the hydrolysis and condensation reaction of TTIP within the micro-emulsion. The average size of synthesized Au doped TiO2 nanoparticle was about in the size range of 15 to 25 nm and the Au particles formed mainly the range of 2 to 10 nm in diameter. The effect of synthesis parameters, such as the molar ratio of water to TTIP and the molar ratio of water to surfactant, are discussed. The synthesized nanopaticles were coated on glass substrate by a spin coating process. The thickness of thin film was about 80 nm. The degradation of MB on a TiO2 thin film was enhanced over 20 % efficiency by the incorporation of Au.
With the miniaturization with both high functionality and high integrity of the probe cards, the highly precise laser punching on the zero-shrinkage high strength substrate has attracted more attention recently. Taper occurrence during laser-punching on green sheets appears as a problem in process. The size (diameter) difference between the entrance hole and the exit hole in tapered holes appeared to be inversely proportional to the hole size itself. To suppress taper occurrence, two-stage punching was adopted as the size of second hole was varied from 70 μm to 79 μm when punching 80 μm via holes on the substrate with thickness of 380 μm. The minimal taper ratio of 11.9 % appeared with second hole size between 70 to 79 μm before sintering. Taper ratio reduced to 7 % after zero-shrinkage sintering. The size difference between first hole and second hole appeared minimal when the size of second hole was 95~97 % to that of first hole.
Recently, a lot of interest has been shown in structural maintenance managements of civil infrastructures. Many researchers have been conducted on various maintenance techniques and repair materials. Among other fiber materials the carbon fiber materials are especially focused on maintenance management of Highway Bridges. Extensive work has been done on Carbon Fiber Sheet (CFS). Nevertheless, Carbon Fiber Strand Sheet (CFSS) is a newly developed material, on which limited work has been done until now. Therefore, in this study bonding the CFSS to RC slab specimen and fatigue resistance evaluation has been conducted. The results demonstrated an increase of 25.3 times more reinforcement of RC slab compared to non-reinforced RC slab. Moreover, compared to CFS-bonded RC slab, The CFSS-bonded RC slab showed 1.2 times greater reinforcement.
According to the results of “Highway Bridges Long Life Repair Plan.” The most serious damage to RC slabs is caused by fatigue deterioration, which results from the driving loads of large-sized vehicles, and aging of materials. In response to this, adhesion reinforcement using carbon fiber sheet is being adopted. In addition, carbon fiber strand sheet that holds the same material characteristics as CFS, but has superior workability, has been developed as a new reinforcement material. However, almost no studies have been conducted on CFSS in relation to fatigue resistance evaluation through fatigue tests under running wheel loads, with the exception of a few by some organizations. Therefore, in this study, specimens with front CFS adhesion reinforcement on the bottom surface of the RC slab and specimens with grid-type CFSS reinforcement were manufactured. Then, fatigue tests under running wheel loads were conducted, and thus fatigue resistance was evaluated using the specimens.