ZnO-doped near-stoichiometric LiNbO3 single crystals of 0.8~1.0 mm diameter and 30~35 mm length were grown by the micro-pulling down (m-PD) method. The structure of the grown crystals was confirmed by powder x-ray diffraction (XRD) patterns. Electron probe micro analysis (EPMA) showed that Zn ions were homogeneously incorporated in grown crystals. The threshold in ZnO doping level was confirmed that an abrupt change in the features of OH- absorption band as doping level reaching about 2 mol%.
The significant color enhancement in low quality Australian natural sapphire has been achieved by a hydrothermalmethod. The optimal conditions for the color enhancement of Australian natural saphire were as follows; hydrothermalreaction temperature: 320~350oC, duration : 3 days, hydrothermal solvent: 2 M NaOH solution. After the hydrothermaltreatment, Australian natural saphires of transparent colors were obtained, and their grades were found to be improvedfrom comercial to midle/top grade by value chart analysis.
Electrostatic spray pyrolysis, a novel fabrication technique, has been used in this study to prepare calcium phosphate nano powders. Final annealing was done at 400oC for 30 min in air. The hydroxyapatite - forming ability of the annealed powder has been evaluated in Eagle's minimum essential medium solution (MEM). X-ray diffraction analysis, field emission - scanning electron microscope, energy dispersive X-ray spectroscope, and Fourier transform infrared spectroscope were used to characterized the annealed powders after immersion in MEM. The powder with an amorphous structure induced hydroxyapatite formation on their surfaces after immersion for 15 days.
The synthesis and characterization of silver colloidal nanoparticles by chemical reduction of silver ions inaqueous AgNO3 using sodium borohydride (NaBH4) as the reducing agent are described. The experimental conditions foraggregation and paricle size of nanosilver particles in water is investigated in terms of concentration of NaBH4, reaction3 and concentration of laponite. Stable nanosilver sol is obtained at thre molar ratio ofNaBH4/AgNO3 in conditions of without laponite. The size of nanosilver particles is increased as the reaction temperature isincreased. The large size of nanosilver sol is obseved as the droping rate of AgNO3 is increased due to the aggregationof initial high local concentration of nanosilver particles. Stable nanosilver sol at high temperature (> 100oC) can beprepared when laponite is used as protective coloid.
The amorphous SiOx nanowires were synthesized by the vapor phase epitaxy (VPE) method. SiOx nanowires were formed on silicon wafer of temperatures ranged from 800~1100oC and nickel thin film was used as a catalyst for the growth of nanowires. A vapor-liquid-solid (VLS) mechanism is responsible for the catalyst-assisted amorphous SiOx nanowires synthesis in this experiment. The SEM images showed cotton-like nanostructure of free standing SiOx nanowires with the length of more than about 10 mm. The SiOx nanowires were confirmed amorphous structure by TEM analysis and EDX spectrum reveals that the nanowires consist of Si and O.
Wel dispersed uniform silver coated silica was prepared by chemical liquid method. The optimum conditions forpreparation of the silver coated silica were as folows: alkaline solution, reaction temperature of 10oC, reaction time of2 hrs, and amount of Ag of 5 wt%. It was found that the prepared silver coated silica were far infrared emissivity of0.916~ 0.918 and antimicrobial effect of 99.9 %.Key words ... ... .. Ag coated silica .... .. . . ... .. .....†.. (... )... , .. , 153-023(2006. 9. 29. .. )(2006. 12. 2. .... )
A series of Sr1 xCaxGa2S4 : Ce,Na phosphors have been synthesized by solid-state reaction. The photoluminescenceand structural properties of Sr1 xCaxGa2S4 : Ce,Na have been examined. The Sr1 xCaxGa2S4 : Ce,Na phosphors have a strongSrGa2S4 : Ce,Na are located at 448 nm and 485 nm. The partial replacement of Sr by Ca in Sr1 xCaxGa2S4 : Ce,Na causes ared shift of emission wavelengths. The Sr1 xCaxGa2S4 : Ce,Na can be used as blue emitting phosphors pumped by the violetLED for fabricating the multi-band white LED.
High velocity of oxy-fuel (HVOF) thermal spray coating is progressively replacing the other classical hard coatings such as chrome plating and ceramic coating by the classical methods, since the very toxic Cr6+ ion is well known as carcinogen causing lung cancer, and the ceramic coatings are brittle. Co-alloy T800 powder is coated on the Inconel 718 substrates by the HVOF coating procesess developed by this laboratory. For the study of the possibility of replacing of chrome plating, the wear properties of HVOF Co-alloy T800 coatings are investigated using the reciprocating sliding tester with a counter sliding SUS 304 ball both at room and at an elevated temperature of 1000oF (538oC). The possibility as durability improvement coating is studied for the application to the high speed spindles vulnerable to frictional heat and wear. Wear mechanisms at the reciprocating sliding wear test are studied for the application to the systems similar to the sliding test such as high speed spindles. Wear debris and frictional coefficients of T800 coatings both at room and at an elevated temperature of 538oC are drastically reduced compared to those of non-coated surface of Inconel 718 substrates. Wear traces and friction coefficients of both coated and non-coated surfaces are drastically reduced at a high temperature of 538oC compared with those at room temperature. These show that the coating is highly recommendable for the durability improvement coating on the surfaces vulnerable to frictional heat and wear.
Coating mixtures of the resin B-H for the application to the desulfurization system of power plant were coated on carbon steels and cured at the temperature of 65oC~80oC. After being contacted with 70 wt% H2SO4 solution of 100oC and 120oC for several hours, their composition, Vicker뭩 hardness and microstructures by SEM were examined. Corrosion resistance of the coating mixtures to H2SO4 solution was related to the content of SO3 in the coated specimens after corrosion test. The lower curing temperature and the shorter curing time the coated specimens went through, the higher corrosion resistance to acid they showed, but the more cracks were developed at higher temperature. It was realized that the corrosion resistance to sulfaric acid solution was increased on the condition of curing temperature above 65oC and curing time above 12 hours at least.