In this paper, we investigated characteristics of etching induced surface morphology variation by wet etching of GaN epilayer were grown on sapphire (0001) substrate by hydride vapor phase epitaxy (HVPE). As a results of scanning electron microscope (SEM) observation, three types of hexagonal etch pits (Edge, Screw, Mixed) were formed by the GaN epilayer thickness variations. A lot of etch pits, attributed to screw and mixed type TD, were observed at thinner epilayer,leading to high etch pit density. On the other hand, the thickness of GaN epilayer increased with the number of etch pits corresponding to edge and mixed dislocations, which are the majority of TDs are observed.
The growth of AlN single crystals of large size and good quality is of prime importance for UV LEDs and power devices applications. However, the crystals having the size of more than 1 inch and high quality have not been reported in the world. In the PVT growth of AlN, the crystal morphology of as grown were important because the preferred orientation of growth of it was evaluated for growth rate increase. In the present study, the AlN single crystals grown by PVT process were evaluated by the side of the growth morphology. Optical microscopic characterization was carried out to observe the shape of the crystals and the growth facets. Furthermore the growth habit of it were discussed by observation of the surface of AlN crystals.
Ammonia decomposition over titanium carbides were investigated using eight different samples which have been synthesized by TPR (temperature-programmed reduction) method of titanium oxide (TiO2) with pure CH4. The resulting materials which were synthesized using wo different heating rates and space velocity exhibited the different surface areas.
These results indicated that the structural properties of these materials have been related to heating rates and space velocity employed. The titanium carbides prepared in this study proved to be active for ammonia decomposition, and the activity changed with the particle size/surface area. These showed the relationship between ammonia decomposition activity and the different active species. Compared to molybdenum carbide, the titanium carbides were one order of magnitude less active,suggesting the correlation between the activity difference and the degree of electron transfer between metals and carbon in metal carbides.
TiO2 can be used optically and is applied on many areas such as gas sensor, solar cell and photocatalysis.
Electrospun nanofibers have received great interest for development and utilization in some novel applications, such as chemical sensors, dye-sensitized solar cell and photo catalysis. In this study, pure TiO2 and Ga-doped TiO2 nanofibers synthesized by a modified electrospinning method. The Ga doped TiO2 solution is prepared by mixing poly vinyl pyrrolidone,ethyl alcohol, and titanium (IV) isopropoxide. By electrospinning these sols, nanofibers were fabricated. These fibers are heat-treated at 800oC in air. The prepared pure TiO2 and Ga-doped TiO2 nanofibers samples were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Raman spectroscopy.
The co-precipitation technique has been applied to synthesize Biphasic Calcium Phosphate (BCP), Mg-BCP and Si-BCP. X-ray diffraction (XRD) and Fourier transformed infrared (FTIR) spectroscopy were used to characterize the structure of synthesized BCP, Mg-BCP and Si-BCP powders. The results have shown that BCP and substitution of magnesium and silicon in the calcium deficient apatites revealed the formation of biphasic mixtures of Hydroxyapatite (HAp)/β-Tricalcium phosphate (β-TCP) ratios after heating at 1000oC. Ionic substituted BCP is able to develop a new apatite phase on the surface in contact with physiological fluids faster than BCP does. An MTT assay indicated that BCP,Mg-BCP, and Si-BCP powders had no cytotoxic effects on MG-63 cells, and that they have good biocompatibility.
Boehmite (AlOOH) powder was synthesized using waste aluminium etching solution. In waste solution, precipitated phase was gibbsite (Al(OH)3), and boehmite (AlOOH) phase was obtained at pH of 7 and 8 controlled by addition of acid.
Boehmite powder was obtained by washing process to remove the Na ion in precipitated solution. Mean particle size of obtained powder was 40 nm. Boehmite phase transformed to α-Al2O3 phase via γ-Al2O3, δ-Al2O3, and θ-Al2O3.
Carbamoylphosphate (CMPO) [CMPO analogue; 2-(diphenylphosphoryl)-N-(3-(triethoxysilyl)propyl)acetamide]silane,as a functional self-assembled molecules, grafted mesoporous silicates were prepared by simple hydrolysis and condensation reaction. Pore sized tailored mesoporous silicates such as MCM-41, SBA-15, or amorphous silica nanoparticles were adopted as host materials. The surface area of ordered mesoporous silicates was ranged from 680 m2/g to 1310 m2/g with different pore diameters that estimated to be ca. 2.3~9.1 nm by BJH method. Among the OMMs host materials, SBA-15(II) has higher loading ratio (~35 wt%) of CMPO derivative than other OMMs. Accessibility to CMPO silane functional groups in the surface of mesoporous silicas was studied by lanthanide ions sorption experiments. All of the CMPO modified OMMs favors the smaller Eu(III) and Nd(III) cations than La(III) for relative larger ionic radius.
Geopolymer was made using magnetic separation fly ash with NaOH(Sodium Hydroxide) and the water glass as alkali activators in this study. Compressive strength of geopolymers ceramics was measured and analyzed according to the type of materials. Under the conditions of fly ash without magnetic separation and 28 day curing after molding, the compressive strength of the geopolymer reached up to 28 MPa.
In order to recycle the coal bottom ashes (denoted as BA) produced from a thermal power plant, the artificial aggregates (denoted as AAs) containing BA and red clay were manufactured, and the physical properties of AAs were studied as a function of particle size of BA and batch compositions. As-received BA had 38 wt% coarse particles of above 2 mm and many unburned carbon mass and porous slag particles were co-existed. So the two particle sizes of BA, the fine (< 100 μm) and coarse (< 2 mm), were prepared by milling and screening process. The AAs containing fine BA sintered at 1100~1200oC had the higher bulk density and lower water absorption compared to the specimen made of coarse BA. The inside core of AAs manufactured by using coarse BA showed nonuniform and porous microstructure, while the AAs made of fine BA had a uniform and dense microstructure. In this research, the AAs containing BA and red clay with various bulk density (1.2~1.7) and water absorption (13~21 %) could be manufactured by controlling the particle size of BA and batch compositions, so the AAs of various physical properties could be applied to the wide fields such as construction/building materials in near future.