In this study, the crystalline property of a-plane GaN epitaxial layer grown on r-plane sapphire by a HVPE method has been investigated according to the V/III ratio and the growth time of multi-step growth. Furthermore, these results were compared with the previous result obtained from the single-step growth of a-plane GaN on r-plane sapphire substrate. In the multi-step growth for a-plane GaN epitaxial layer on r-plane sapphire, the FWHM values of rocking curve in GaN epitaxial layer were decreased as the HCl source flow rate and the growth time were increased. The void formed in epitaxial layer was continuously decreased as the growth time in first step and second step using a higher HCl flow rate was increased. As a result, the GaN layer obtained with the longest growth time on the first step and second step exhibited the lowest FWHM values of 584 arcsec and the smallest dependence of azimuth angle.
In this work, tin oxides were obtained by the liquid reduction precipitation method and hydrothermal process using SnCl2 · 2H2O, N2H4, and NaOH. Tin oxide crystals having different sizes and morphologies could be achieved. The powders were characterized by X-ray diffraction (XRD) and Field Emission Scanning Electron Microscopy (FE-SEM).
Depending on the molar ratio of the raw materials, tin oxide crystalline with the spherical and rectangular plate-like shape could be obtained, the crystal phase was SnO and Sn6O4(OH)4. And the obtained SnO crystals by a hydrothermal reaction showed various shapes, such as, spherical, plate-like and flower-like architectures depending on the temperature conditions.
Each year, more than seven hundred thousand tons of copper slag are generated in Korea as a byproduct during the production of copper. Due to the large amount of copper slag produced, there has been increased interest in the use of copper slag as a construction material. To evaluate the potential of copper slag as a construction material, laboratory evaluations were conducted in this study, and three particle shapes and replacement rates of river sand were selected as experimental variables. Strength, air-void characteristics, and sulfuric acid resistance were the three properties evaluated to assess whether copper slag can be used as a construction material. Test results indicate that the gradation of copper slag has an effect on strength, and the maximum strength was achieved when 60 % of river sand was replaced with copper slag. In addition, when compared with ordinary Portland cement mortar, replacing river sand with copper slag reduced air void size and increased sulfuric acid resistance.
Monodispersed ZnGa2O4 microspheres were synthesized by a facile two-step process consisting of a solvothermal method and calcination process. The prepared monodispersed ZnGa2O4 microspheres were aggregated into 3D microstructures by self-assembly with a large number of small ZnGa2O4 particles generated in nucleation. This nucleation and self-assembly making hierarchical microstructures were depended on the concentration of PEG (polyethylene glycol) due to CAC (critical aggregation concentration) theory. And also we controlled the amount of zinc acetate to make pure ZnGa2O4 phase. Additionally, to fix the optimized calcination condition, sample was characterized by TG-DTA to prove the thermal property in the calcination process and by FT-IR to identify the changes of functional group bonding between each element of the ZnGa2O4 precursor and oxide calcined at 900 o C for 1 h.
CeO2 is used as a co-catalyst with TiO2 to improve the catalytic activity of MnOx and characterization of nanosized powder is identified with de-NOx efficiency. A comparison between MnOx-CeO2/TiO2 and single CeO2 was conducted in terms of microstructural analysis to observe the behavior of CeO2 in the ternary catalyst. The MnOx-CeO2/TiO2 catalyst was synthesized by sol-gel method and the average particle size of the single CeO2 is about 285 μm due to the low thermal stability, whereas the particle size MnOx-CeO2/TiO2 is about 130 nm. The strong interaction between Ce and Ti was identified through the EDS mapping by transmission electron microscopy (TEM). The improvement about 20 % of de-NOx efficiency is observed in the low-temperature (150 o C~250 o C) and vigorous oxygen exchange by well-dispersed CeO2 is the reason of catalytic activity improvement.
The effect of temperature and pressure in the nitrogen ambient furnace on bulk micro defect (BMD) and denuded zone (Dz) is experimentally investigated. It is found that as pressure increases, Dz depth increases with a small decrease of BMD density in the range of temperature, 100~300 o C. BMD density with hot isostatic pressure treatment (HIP) at temperature of 850 o C is higher than that without HIP while Dz depth is lower due to much higher BMD density. As the pressure increases, BMD density is increased and saturated to a critical value, and Dz depth increases even if BMD density is saturated. The concentration of nitrogen increases near the surface with increasing pressure, and the peak of the concentration moves closer to the surface. The nitrogen is gathered near the surface, and does not become in-diffusion to the bulk of the wafer. The silicon nitride layer near the surface prevents to inject the additional nitrogen into the bulk of the wafer across the layer. The nitrogen does not affect the formation of BMD. On the other hand, the oxygen is moved into the bulk of the wafer by increasing pressure. Dz depth from the surface is extended into the bulk because the nuclei of BMD move into the bulk of the wafer.
Ti alloys have been used for orthopedic devices, automobile and aircraft because it has several beneficial properties such as a low density, a low modulus of elasticity, excellent high-temperature strength, excellent corrosion resistance and biocompatibility. In this study, Ti-64 composition (6 wt% Al, 4 wt% V) is investigated as a representative Tialloy system on the crystallographic characteristics and microstructure. We investigated crystal structure of the Ti-64 sample by XRD, and analyzed microstructure by compositional differences measured using FE-SEM and EDX.