Sapphire single crystals have been highlighted for epitaxial gallium nitride films in high-power laser and light emitting diode (LED) industries. Among the many crystal growth methods, the Kyropoulos process is an excellent commercial method for growing larger, high-optical-quality sapphire crystals with fewer defects. Because the properties and growth behavior of sapphire crystals are influenced largely by the temperature distribution and convection of molten sapphire during the manufacturing process, accurate predictions of the thermal fields and melt flow behavior are essential to design and optimize the Kyropoulos crystal growth process. In this study, computational fluid dynamic simulations were performed to examine the effects of the crucible geometry aspect ratio on melt convection during Kyropoulos sapphire crystal growth. The results through the evolution of various growth parameters on the temperature and velocity fields and convexity of the crystallization interface based on finite volume element simulations show that lower aspect ratio of the crucible geometry can be helpful for the quality of sapphire single crystal.
The properties of Al-doped ZnO (AZO) films were investigated as a function of H2/(Ar + H2) gas ratio using an AZO (2 wt% Al2O3) ceramic target in a radio frequency (RF) magnetron sputtering system. The deposition process was done at 200oC and in 2 × 10−2 Torr working pressure and with various ratios of H2/(Ar + H2) gas. During the AZO film deposition process, partial H2 gas affected the AZO film characteristics. The electron resistivity (~9.21 × 10−4 Ωcm) was lowest and mobility (~17.8 cm2/Vs) was highest in AZO films when the H2/(Ar + H2) gas ratio was 2.5 %. When the H2/(Ar + H2) gas ratio was increased above 2.5 %, the electron resistivity increased and mobility decreased with increasing H2/(Ar + H2) gas ratio in AZO films. The carrier concentration increased with increasing H2/(Ar + H2) gas ratio from 0 % to 7.5 %. This phenomenon was explained by reaction of hydrogen and oxygen and additional formation of oxygen vacancy.
The average optical transmission in the visible light wavelength region over 90 % and an orientation of the deposition was  orientation for AZO films grown with all H2/(Ar + H2) gas ratios.
To achieve low-cost and high-efficiency of thin-film solar cells applications, the sol-gel method that can be coated on a large area substrate, obtain homogeneous thin films of high purity was used. We studied structural and optical characteristics versus annealing temperature of Cu2ZnSnS4 which has kesterite structure by substitution low-cost sulfur (S)instead of high-cost selenium (Se). By analyzing XRD patterns, main peak was observed at 2θ = 28.5o when Zn/Sn ratio is 0.8/1.2. And when we observed kesterite structure which has orientation of (112) direction, the more annealing temperature increase the bigger strength of (112) direction is. Cu2ZnSnS4 thin film showed characteristics of kesterite structure at 550oC.
And when we calculated lattice constant, a = 5.5047 and c = 11.014 as same JCPDS (Joint Committee on Powder Standards) data measured. We measured optical transmittance to analyze optical characteristics. Optical transmittance was lower than 65 % at visible ray (λ = 380~770 nm).
Recently the preparation magnetic nanoparticles by a pulsed laser ablation in liquid has gained much attention because it is easy to control experimental parameters. Iron oxide magnetic nanoparticles have been prepared by a pulsed laser ablation of α-Fe2O3 target in ethanol at different magnitude of laser energy of 1, 20, 40 and 80 mJ/pulse. It revealed that particle size increases with increasing laser energy. It could be concluded that 40 mJ/pulse is an optimum laser energy for the preparation of iron oxide nanoparticles with uniform size distribution. The nanoparticles are homogeneously dispersed in ethanol and their stability maintained for several months.
Natural hydroxyapatite powder was obtained from the calcination of bovine bones and its porous compacts were fabricated by pressureless sintering at 1100 and 1200oC for 1h. To evaluate and compare their biocompatibility with porosity, we investigated the support of osteoblast cells growth and cytotoxicity using the MG-63 cell line model in vitro.
Sintered hydroxyapatite ceramics have a porous microstructure with a relative density of 65 % at 1100oC and 82 % at 1200oC. Cells adherence to the surface of hydroxyapatite ceramics was observed in a day after the cell culture, and the spreading of cytoplasm around the nucleus was shown after 3 day cell culture. Most of cells were extended to the surface of hydroxyapatite through the wide area. Cell viability was nearly the same till 3 days culturing. But the rate of cell growth is higher in the specimen sintered at 1100oC than that of 1200oC. It indicates that the porosity is an important factor to enhance the cell viability in the porous hydroxyapatite ceramics derived from bovine bones.
Carbon dioxide (CO2) could be stored in the form of Ca and Mg compounds including alkaline earth metal by carbonation. The possibility of CO2 storage was tested by using desulfurized ash from fluidized bed type boiler as raw material. Autoclave was used for maintaining the reaction pressure and temperature for the carbonation. The analysis of weight change rate, XRD, and TG/DTA proved that more than 15 % of carbonation rate was obtained under 10 kgf/cm2and 120oC-10 min.
In this study, geopolymer was prepared with reject ash and blast furnace slag using NaOH as an alkali activator and water glass. The aim of this study was to investigate the compressive strength variation according to the contents of NaOH and water glass and replacement ratio of reject ash (RA) and blast furnace slag (BS). The compressive strength measured after 28 days was 38.91 MPa for the geopolymer which consist of 100 % of BS with 1 wt% NaOH and 3 wt%water glass. The major factor for improving compressive strength was the alkali activator proportion and the replacement ratio of RA and BS.
The purpose of this study is to improve recycling rate of the coal reject ash by investigating bloating mechanism for artificial lightweight aggregate of reject ash. In this study, we use reject ash (R/A) and dredged soil (D/S)as raw materials. The artificial lightweight aggregates were formed by plastic forming (φ = 10 mm) and sintered by temperature raising method at different temperatures (between 1200 and 1275oC). The physical properties of the aggregates such as bulk specific gravity, adsorption and microstructure of surface and cross-section are investigated with the sintering temperature and rate of R/A-D/S contents. As the result of the bulk specific gravity graphs, we can found out the inflection point at content of R/A 80 wt.%. From the microstructure images, we considered the artificial lightweight aggregates content of R/A over 80 wt.% are distributed numerous uniform micro-pores by vitrification without Black Core and the artificial lightweight aggregates of R/A below 80wt.% are distributed macro-pores with Black Core.