AlN buffer layers have been used for the growth of GaN layers on Si substrates. However, the doping of high concentration of carriers into AlN layers is still not easy, therefore it may cause the increase of series resistance when it is used for the electrical or optical devices. In this work, to improve such a problem, the growth of GaN layers on Si substrates were performed using metal buffer layers instead of AlN buffer layer. We tried combinations of Ti, Al, Cr and Au as metal buffer layers for the growth of GaN on Si substrates. Surface morphology was measured by optical microscope and scanning electron microscope (SEM), and optical properties and crystalline quality were measured by photoluminescence (PL) and X-ray diffractometer (XRD), respectively. Electrical resistances for both cases of AlN and metal buffer layer were compared by current-voltage (I-V) measurement.
Titanium dioxides nanoparticles coated aluminum oxide powders were fabricated by pulsed laser deposition (PLD) with Nd : YAG laser at 266 nm. The Pulse laser energy is 100 mJ/pulse. During the irradiation of the focused laser on the TiO2 target, Ar gas is supplied into the chamber. The gas pressure is varied in a range of 1 × 10−2 to 100 Pa.
Titanium dioxides nanoparticles deposited aluminum oxide powders were characterized by using energy dispersive X-ray spectroscopy (EDX), high resolution transmission electron microscopy (HR-TEM), in order to understand the effect of Ar background gas on surface morphology and properties of the powders. The coated TiO2 nanoparticles had nanosized spherical shape and the crystallite sizes of 10~30 nm. The morphology of coated TiO2 nanoparticles is not affected by gas pressure. However, the particle size and crystallinity slightly increased with the increase of gas pressure. According to this technique, the size and crystallinity of nanoparticles can be easily controlled by controlling pressure during the laser irradiation.
Even though a rough diamond shape is irregular and rugged, it is easy to be processed to make gem, shaped facets (table, crown, pavilion and girdle) were precisely treated because they influence on the evaluation of diamond grading. Those specifications suitable for the standard round brilliant cut diamond polishing were investigated and in 95 %statistical confidence interval, standard deviation, mean and acceptable tolerance were examined. According to these variables (size, angle, depth, and thickness) distribution, the frequency analysis of ratings and proportions were compared with each other. The correlation between each variables and the evidence of influence represented in proportion were determined by the regression analysis applying LSM (Least Square Method). In this research, it was recognized that table sizes of the diamond jewels and pavilion depth (in %) influence the rating decision and in particular, the depth of pavilion acting as the main factor of proportions, also plays an important role in optical phenomena.
The glass of E-glass fiber composition was fabricated by using refused coal ore which is obtained as by-product from Dogye coal mine in Samcheok. We used silica-alumina refused coal ore which has low carbon content relatively, and the amount of refused coal ore has been changed from 0 to 35 % in batch composition. E-glass was fabricated by the melting of mixed batch materials at 1550oC for 2 hrs with different refused coal ore composition of 0~35 %. We obtained a transparent and clear glass with high visible light transmittance value of 81~84%, thermal expansion coefficient of 5.39~5.61 × 10−6/oC and softening point of 851~860oC. The glass fiber samples were also obtained through fiberizing equipment at 1150oC, and tested chemical resistance and tensile strength to evaluate the mechanical property as a reinforced glass fiber of composite material. As the result, we identified the properties of E-glass fiber by using refused coal ore are plenty good enough compare to that of normal Eglass without refused coal ore, and confirmed the possibility of refused coal ore as for the raw material of E-glass fiber.
Single phase crystalline powders of Mg3Sb2 and Mg3Bi2 were prepared by mechanical alloying Mg, Sb and Bi metals with planetary ball milling for 24~48 h. The compositions of starting raw materials for single phase Mg3Sb2 and Mg3Bi2 were 3Mg : 1.8Sb and 3Mg : 1.6Bi, respectively. Two types of mechanically alloyed powders obtained were mixed at some ratios for the fabrication of Mg3Sb2-Mg3Bi2 composites and then hot pressed under uniaxial pressure of 70 MPa at 723 K for 1 h. The main phase of composites was a stable phase similar to Mg3Bi2 phase with a small amount of Bi phase. The distributions of Sb and Bi elements on EDS mapping images were discontinuous and their compositional contours were clear, which means that the hot pressed specimens were composites composed of two compounds of Mg3Sb2 and Mg3Bi2.
Novel Sr-Y-Si-Oxynitride yellow phosphors were synthesized and the effect of calcination temperature, reduction temperature and Eu2+ concentration on their luminescence properties were studied. Optimal temperature conditions were found to be 1400oC and 1300oC for solid-state reaction and reduction, respectively. The synthesized Ba9Y2 + ySi6O24 − 3yN3y : Eu2+phosphors showed a single intense broadband emission in the range of 571~587 nm for 450 nm excitation light source. The highest luminescence intensity was obtained with Eu concentration of 3 mol% and concentration quenching was observed beyond 5 mol%. FE-SEM and PSA showed that the synthesized phosphors consists of particles with an average size of ~8.2 μm.
The coal bottom ash and reject ash discharged from a coal-fired power plant are difficult to recycle so most of them are mainly landfill-disposed. In this study, the artificial aggregate were produced using reject ash, bottom ash and dredged soil emitted from the coal-fired power plant in Korea and the effect of experimental factors on the bloating behavior and the properties of the aggregates were analyzed. In particular, a lot of unburned carbon in the reject ash was removed by calcination and the activated carbon was added to batch powders then the dependence of those process upon bloating properties of artificial aggregate were investigated. For this purpose, the specific gravity and water absorption values of artificial aggregates were investigated in conjunction with microstructural observations. This study could contribute to increase the recycling rate of the reject ash.
It is well known that fatigue failure occur on welded structures in industrial application due to the repetitive load force. In order to decrease the fatigue failure, we analysed the mechanical properties based on their structural aspect,roll steel (SS 400) welded onto stainless steels (STS 304) by CO2 gas as well as structure roll steel welded onto itself. We compared the hardness, tensile and fatigue properties with two kinds of samples which had no defects on the welding part observed by X-ray topographic analysis. It was recognized that the tensile and fatigue strength of SS 400 welded onto itself by CO2 gas was higher than that of SS 400 welded onto STS 304.