• Korean Journal of Materials Research
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• v.19 no.4
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• pp.207-211
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• 2009

In this study, we attempted to develop a convenient aluminizing process, using Al-Ti mixed slurry as an aluminum source, to control the Al content of the aluminized layer as a result of a one-step process and can be widely adopted for coating complex-shaped components. The aluminizing process was carried out by the heat treatment on disc and rod shaped S45C steel substrates with Al-Ti mixed slurries that were composed of various mixed ratios (wt%) of Al and Ti powders. The surface of the resultant aluminized layer was relatively smooth with no obvious cracks. The aluminized layers mainly contain an Fe-Al compound as the bulk phase. However, the Al concentration and the thickness of the aluminized layer gradually decrease as the Ti proportion among Al-Ti mixed slurries increases. It has also been shown that the Al-Ti compound layer, which formed on the substrate during heat treatment, easily separates from the substrate. In addition, the incorporation of Ti into the substrate surface during heat treatment was not observed.

• Journal of Korea Foundry Society
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• v.14 no.6
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• pp.530-540
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• 1994

Aluminium-silicon alloy(JIS AC8A) matrix composites reinforced with SiC particles were fabricated by spray-cast forming process, and the microstructure of powders and preforms produced were studied by using an optical and scanning electron microscopy. SiC particles were co-sprayed by mixed phase injection method during the spray casting process. Most of the composite powders formed by this mixed phase injection method exhibit morphology of particle-embedded type, and some exhibits the morphology of particle attached type due to additional attachment of the SiC particles on the surface of the powders in flight. The preforms deposited were resulted in dispersed type microstructure. The pre-solidified droplets and the deposited preform of SiC-reinforced aluminium alloy exhibit finer equiaxed grain size than that of unreinforced aluminium alloy. Eutectic silicons of granular type are crystallized at the corner of the aluminum grains in the preforms deposited, and some SiC particles seem to act as nucleation sites for primary/eutectic silicon during solidification. Such primary/eutectic silicons seem to retard grain growth during the continued spray casting process. It is envisaged from the microstructural observations for the deposited preform that the resultant distribution of SiC injected particles in the Al-Si microsturcture is affected by the amount of liquid phase in the top part of the preform and by the solidification rate of the preform deposited.

• Journal of the Korean Ceramic Society
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• v.37 no.5
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• pp.473-478
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• 2000

The TiO2 powder with the values of the large specific surface area more than 150$m^2$/g has been prepared with the homogeneous precipitation process below 5$0^{\circ}C$ and its formation mechanism was investigated using the SEM, TEM and Raman Spectroscopy. With the spontaneous hydrolysis of aqueous TiOCl2 solutions, all the precipitates were fully and homogeneously crystallized with the rutile TiO2 phase simply by heating, which as transformed to the anatase TiO2 phase as increasing the addition of SO42- ions to the aqueous TiOCl2 solution. The precipitates were formed with spherical secondary particles which consisted of acicular, spherical and mixed primary particles corresponding to the rutile, anatase and mixed phases, respectively. It can be thought that the formation and phase determination of crystalline TiO2 powders even at ambient temperature would be related with the existence of the capillary force. This force might be varied depending on the shape change of the primary particles.

• Journal of the Korean Society for Heat Treatment
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• v.31 no.3
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• pp.104-110
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• 2018

The effects of heat treatment time and cooling method on microstructure and mechanical property of Cu-22wt%Sn alloy were discussed. ${\alpha}+{\delta}$ mixed phase structure was obtained in air-cooled specimens after heat treatment at 775, 750, and $700^{\circ}C$ for 1 hour. On the other hand, in water-cooled specimens, ${\alpha}+{\beta}^{\prime}$ martensite mixed phase was obtained. In the case of water-cooled specimens, the hardness value decreased with decreasing heat treatment temperature because the volume fraction of ${\alpha}$ phase with low hardness value increased as the heat treatment temperature decreased. In water-cooled specimen after heat treatment at $600^{\circ}C$, ${\gamma}^{\prime}$ martensite was formed instead of ${\beta}^{\prime}$ martensite. The hardness value of ${\gamma}^{\prime}$ martensite was lower than those of ${\beta}^{\prime}$ and ${\delta}$ phases.

• Journal of the Korean Ceramic Society
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• v.34 no.3
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• pp.249-256
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• 1997

The effect of process parameter of plasma assisted chemical vapor deposition (PACVD) on the variation of the ratio between cubic boron nitride (c-BN) and hexagonal boron nitride (h-BN) in the film was in-vestigated. The plasma was generated by electric power with the frequency between 100 and 500 KHz. BCl3 and NH3 were used as a boron and nitrogen source respectively and Ar and hydrogen were added as a car-rier gas. Films were composed of h-BN and c-BN and its ratio varied with the magnitude of process parameters, voltage of the electric power, substrate bias voltage, reaction pressure, gas composition, sub-strate temperature. TEM observation showed that h-BN phase was amorphous while crystalline c-BN par-ticle was imbedded in h-BN matrix in the case of c-BN and h-BN mixed film.

• Proceedings of the KIEE Conference
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• 2007.11c
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• pp.88-92
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• 2007

In this paper, the basic experiment, electrolytic cell design and basic manufacturing have been made to interpret the characteristics of Hydrogen-Oxygen-Gas-Generator. As for the detailed matters, the data research on basic technology on Hydrogen-Oxygen-Gas and analysis on characteristics of Hydrogen-Oxygen-Gas from basic experiment. Also the experiment of characteristics and comparative evaluation between constant current source using IGBT converter from existing method and constant current source using new phase shift PWM control method converter. As results when it has injected constant DC current, we has compared Gas quantities by variable ripple frequencies using phase shift PWM control method converter. Therefore, in linear region, it has not different Gas quantities by constant DC current and by phase shift PWM control method converter. Also, it has increased Gas quantities wilder linear region when put ripple frequency at saturation region. Through, Gas quantities and input power, it has acquired higher input power per Gas quantities at put pulse curren. Therefore, when designing converter or inverter for electrolysis, which has ripple current.

• Journal of the Korean Applied Science and Technology
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• v.19 no.4
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• pp.339-348
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• 2002

Self-diffusion coefficients of colloidal ass9Ciation structures in the aqueous solutions of anionic ammonium dodecyl sulfate (ADS) and cationic octadecyltrimethylammonium chloride (OTAC) surfactants were measured by pulsed-gradient spin echo NMR. The results were interpreted on the basis of the ADS/OTAC/water phase diagram. Crossing the phase boundaries, significant changes in self diffusion coefficients were observed and well correlated to the phase diagram. For the micelles their apparent radii were obtained from Stokes-Einstein equation. Their values were 15 for the ADS micelles and 54 ${{\AA}}$ for the OTAC micelles, respectively. For vesicles which were formed spontaneously at different relative amounts of the surfactants and total surfactant concentrations, the radius was measured as 50 to 200 nm. This result is in fair agreement with those by TEM and light scattering.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.19 no.4
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• pp.322-327
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• 2006

CdS films have been prepared on polycarbonate, polyethylene terephthalate, and Coming 7059 substrates by r.f magnetron sputtering technique at room temperature. A comparison of the properties of the films deposited on polymer and glass substrates was performed. In addition, the influence of the sputter power on the structural and optical properties of these films was evaluated. The XRD measurements revealed that CdS films were polycrystalline and retained the mixed structure of hexagonal wurtzite and cubic phase, regardless of substrate types. As the sputter power was increased from 75 to 150 Watt, the structure of CdS films was converted from the mixed of hexagonal and cubic phase to hexagonal phase. The morphology of CdS films is found to be continuous and dense. Also, the grain of CdS films is larger with increasing the sputter power. The average transmittance exceeded 80 % in the visible spectrum for all films and decreases slightly with the sputter power.

• Applied Chemistry for Engineering
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• v.16 no.5
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• pp.614-619
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• 2005

The water-soluble defoamers were fabricated by the mixing polyol, modified silicon resin, silicon resin and surfactant. For the defoamers, the various properties such as phase-separation time, viscosity and defoamerability were examined. The phase-saparation time of PPG mixtures was found to be PPG 400>PPG 3,000>PPG 1000. When PPG 1000 was mixed, mixtures represented the excellent defoamerability. The phase-saparation time of silicon resin mixtures was TSF-451-350>TSF-451-200>TSF-451-50. As more of high molecular silicon resin was mixed, the resulting mixtues showed reduced defoamerability. When the TSF-451-50 was mixed, the mixture's volume was increased because of the reduction of solubility. The modified silicon resin was smoothly dispersed in water, but the compatibility with PPG was not good. The defoamerability of surfactant was SPAN 20>SPAN 60>SPAN 80. SPAN 80 showed good miscibility for the silicon resin, but not good for YAS 6406 or PPG 1000.

• Clean Technology
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• v.22 no.1
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• pp.9-15
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• 2016

xAl-yZr mixed oxide catalysts with different molar ratios of Al/(Al+Zr) were prepared by a co-precipitation method and its catalytic performance was compared in the iso-propanol dehydration as a model reaction. The catalysts were characterized by X-ray diffraction (XRD), differential thermal analysis (DTA), N₂ adsorprion-desorption, NH₃ temperature programmed desorption (NH₃-TPD), and iso-propanol TPD analyses. The addition of Al into ZrO₂ promoted the formation of relatively small particles with large surface areas and retarded the transformation of teragonal phase to monoclnic phase. NH₃-TPD results revealed that the relative acidity of the catalysts increased along with the increase of Al molar ratio. The catalytic activity for the dehydration of iso-propanol to propylene was also increased with the same tendency. The catalytic activity could be correlated with high surface area, acidity and easy desorption of iso-propanol.