Polar and non-polar GaN was grown by the HVPE on various substrates and influence of polarity has been
investigated. The 10 μm thickness GaN were grown by HVPE is along A-plane (1120), C-plane (0001) and M-Plane
(1010) sapphire substrate respectively. Surface properties were observed by optical microscope and atomic force microscopy.
High resolution X-ray diffraction (HR-XRD) confirms the wurtzite structure. The donor band exciton peak located at
~3.4 eV and also located yellow luminescence peak at 2.2 eV. The polarity of the GaN film has a strong influence on the
morphology and the optical properties.
GaN films were grown on the vertical and horizontal reactors by the hydride vapour phase epitaxy (HVPE). The structural and optical characteristics of the GaN films were investigated depending on the reactor-type. GaN epilayers were characterized by double crystal X-ray diffraction (DC-XRD), transmission electron microscopy (TEM) and photoluminescence (PL). Surface defects of two kinds of the GaN films were revealed by the wet chemical etching
method, using H₃PO₄ acid at 200℃ for 8 minutes. Hexagonal etch pits were analyzed by optical microscopy and SEM. Etch pit densities were calculated to be approximately 1.4×10
7 and 1.2×106cm-² for GaN layers grown on horizontal and vertical reactors, respectively. Those results show GaN grown in the vertical reactor having a better quality of optical
properties and crystallinity than that in the horizontal reactor.
Four different thin films were made by depositing PZ and PT in different stacking sequences. PZ and PT phases
are preferably co-existed in sample A and C that are annealing after each coatings. The sample B and D, on the other
hands, have tendency toward the PZT phase after co-firing the sample. The sample B that started from PT stacking first
was more stable PZT phase than that of PZ first sample D.
Novel green long persistent phosphors of CaZrO₃: Ho³+ have been synthesized at high temperature with weakreduction atmosphere by traditional solid state reaction method. The role of H₃BO₃ as flux and the suitable concentration of Ho as activator on the CaZrO₃: Ho³+ long persistent phosphors has been investigated. Crystals of Ho³+ doped CaZrO₃longpersistent phosphores were characterized by fluorescence spectrophotometer and photoluminescence (PL). The main emissionspectra of 546 nm peak was revealed through synthesizing at high temperature in N₂gas atmosphere. The afterglowemission spectra of CaZrO₃: Ho³+ long persistent phosphores arise at 546 nm peak of narow range. because that revealedpure gren color. Green long persistent phosphors have been observed in the system for over 5 h after UV irradiation(254 nm). The main emission peak was ascribed to Ho³+ ions transition from 5F4, 5S2 →5I3, and the afterglow may be3 host lattice.
Microstructure of glass-ceramics obtained by heat treating silicate glass containing 50 wt% electric arc furnace dust (EAF dust) and nucleation agents were observed. The crystallization temperature, Tc of glassy specimen measured around 850℃ from different thermal analysis, so the heat treatment condition to obtain glass-ceramic specimen was selected as 950℃/15 hr. The nucleation agent, TiO₂showed the superior effect on enhancing franklinite crystal growth which has stronger mechanical properties and more durable chemical resistance than willemite phase. Some specimens containing TiO₂had the augite crystal phase and increasing TiO₂ amount decreased a fraction of willemite and increased a franklinite.
Especially, the specimen with 5 wt% TiO2 showed no willemite crystal phase and 1~2 μm franklinite crystals dispersed uniformly in glassy matrix. Also, the specimens containing 5 wt% TiO2 mixed with Fe₂O₃ showed a dendrite-shaped franklinite crystals caused by coalescence of small crystallites.
The partial phase diagram of NaNO3-NaCl system was investigated and the eutectic temperature was determined as 294.5oC. A typical rod eutectics of NaNO3-4.56 wt%NaCl was directionally solidified. The results of interrod spacing,
λE, as a function of growth velocity, V, were obtained as λE V 0.39= 5.26 (temperature gradient, Gl = 21.4℃/mm) and λEV0.32= 5.45 (Gl = 3.9℃/mm) and the exponent numbers of growth velocity were smaller than the theoretical value, 1/2. The sample rotation applied during directional solidification made the interrod spacing decrease slightly.
If the properties of artificial lightweight agregates produced by rotary kiln can be predicted by using asimulator equipped with a small electric furnace and a specially designed device for specimen movement, large amount ofraw materials and plenty of test time can be saved to produce test products of lightweight aggregates. In this study aown design and the properties of lightweight aggregates produced by both the simulator and rotary kiln were compared tospeculate its usefulness. The average diameter of aggregates was 8 m and atmosphere in the furnace was controled bythe amount of carbon powders. Specific gravity, absorption rate (%), black-core area in the cross-sectional view of bothaggregates were measured and compared. Unlike oxydizing atmosphere, both specific gravity and absorption rate of theagregates sintered at reducing atmosphere were increased with increasing carbon addition. It is concluded that the sinteringatmosphere was the closest to that of the rotary kiln when the carbon adition was 0.7 g to make a reducing atmospherein the furnace and the porperties of both agregates was also similar to each other. Key words Rotary kiln, Lightweight aggregate, Simulator, Sintering atmosphere
This study is to establish the coating technique for synthetic mica and to prepare synthetic mica with the nonaqueous
property. The surface coating of synthetic mica is prepared with stearic acid using the high speed stirrer. The
characterizations for mica powders coated the stearic acid are carried out by the deposition test, XRD and SEM. The
results of research could be coated the stearic acid on the mica by 1600 rpm/min at 70℃ for 10 min. From the observation
of SEM was found that the non-aqueous property mica could obtained by mixture ratios for stearic acid and mica, the
inner temperature and rotation speed of the stirrer but treated time be unrelated.