• 한국수소및신에너지학회논문집
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• 제5권2호
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• pp.59-63
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• 1994

Thermally evaporated Pd films on substrate were hydrogenated upto 1 bar of hydrogen gas at room temperature. Thickness dependence on hydrogenation on Pd film is examined in the thickness range between $60{\AA}$ and $800{\AA}$. Hydrogenation kinetics of thinner films(thinner than $500{\AA}$) and that of thicker films are different. Thin film(thickness < $200{\AA}$, substrate temp. = RT) showed recrystallization due to hydrogen induced heat. Hydrogen was absorbed by chemisorption process in ${\alpha}$ phase of thinner films, and diffusion process in ${\alpha}'$ phase of thicker films respectively.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2001년도 Proceedings ICPE 01 2001 International Conference on Power Electronics
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• pp.126-131
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• 2001

This paper deals with implementation of inverter systems for DC power regeneration, which can regenerate the excessive DC power from DC bus line to AC supply in substations for traction systems. From the viewpoint of both power capacity and switching losses, a three-phase square-wave inverter system is adopted. To control the regenerated power, the magnitude and phase of fundamental output voltages should be appropriately controlled in spite of the variation of input DC voltage. Inverters are operated with modified a-conduction mode to fix the potential of each arm. The overall system consists of the line-to-line voltage and line current sensors, an actual power calculator using d-q transformation method, a complex power controller with PI control scheme, a gating signal generator for modified $\alpha-conduction\;mode\;with\;\delta\;and\;\alpha$, a DPLL for frequency followup, and power circuit.

• 한국재료학회지
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• 제4권6호
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• pp.695-703
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• 1994

4-(4-Alkyloxybenzoyloxy)-4'-(S)-$\alpha$-halo-alkanoyloxybipeny1계열 액정화합물이 합성되고, 그들의 액정성질이 조사되었다. 합성된 바이페닐 에스터계열 화합물들은 키랄 스메틱 C상 뿐 아니라 키랄 네마틱 및 스메틱 A상을 나타내고, $10^{-7}\textrm{cm}^2$ 이상의 큰 자발분극을 나타내었다.

• 한국세라믹학회지
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• 제32권12호
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• pp.1417-1423
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• 1995

α/β sialon based composites containing silicon nitride whisker and silicon carbide platelet were fabricated by hot pressing. Effect of the reinforcing agents on the α to β phase transformation of the sialon as well as on the mechanical properties was investigated. Silicon nitride whisker and silicon carbide platelet promoted the phse transformation. TEM/EDS analysis revealed that the grain containing the whisker had 'core-rim' structure; core being high purity Si3N4 whisker and rim being β-sialon. Flexural strength of the composite decreased with the reinforcement addition which, on the other hand, improved fracture toughness of it. High temperature strength was measured at 1300℃ to be about 130 MPa lower than that measured at RT for the whisker reinforced composites.

• Macromolecular Research
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• 제8권6호
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• pp.247-252
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• 2000

Suspension polymerizations of styrene were conducted in the aqueous phase with tricalcium phosphate (TCP) as a stabilizer and $\alpha$, $\alpha$'-azobis(isobutyronitrile) (AIBN) as an initiator. Various amounts of initiator and stabilizer were selected and the reaction was carried out at a selected temperature between 60 to 80 $\^{C}$. It was found that the combination of 5 wt% stabilizer and 2.427$\times$10$\^$-3/ mol/L of costabilizer is the minimum amount for suspension polymerization reaction to produce particles in the aqueous phase. Particles were found to be polydisperse in diameter, regardless of reaction conditions. Class transitions were observed to be around 95$\^{C}$, nearly independent of reaction temperature and initiator. Homogenizer was found to be essential in forming particles in the proximity of tens of micrometers in diameter in suspension polymerization with TCP as stabilizer.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2007년도 추계학술대회 논문집
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• pp.150-153
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• 2007

Apply electromagnetic stirring system to making rheology slurry of Al7075. This experiment has important element which is the relation between solid fraction percent and melt temperature of Al7075. The rheology slurry of Al7075 eliminated liquid phase to include alloying element of copper and zinc by squeeze casting process. In result the most structure was composed entirely of globular primary $\alpha$. Used this material for this study. This study made a comparison of mechanical property according to heat treatment T6 at each melt temperature ($619^{\circ}C$ and $615^{\circ}C$). The microstructure and component are observed how heat treatment T6 weight with the mechanical property by SEM-EDS.

• 한국분말재료학회지
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• 제5권1호
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• pp.22-27
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• 1998

The effect of the $\alpha$/$\beta$ phase fraction on the mechanical properties in silicon nitrides was investigated in part 1. In part II, we describe the role of microstructure on the mechanical properties and contact damage of silicon nitrides with coarse/equiaxed and coarse/elongated microstructures. Grain sizes and shapes were controlled by starting powder. Hertzian indentation using spherical indenter was also used to investigate contact damage behavior. Cone cracks from the spherical indentation were suppressed when the silicon nitride contains coarse and elongated grains. Coarse and elongated grains played an important role of cone crack suppression. The size of quasi-plastic zone does not depend on grain size or shape but depends on the fraction of $\alpha$/$\beta$ phase. A quasi-plastic zone was consisting of microcracks by shear stress during indentation.

• 한국세라믹학회지
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• 제27권5호
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• pp.625-630
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• 1990

Cordierite powders were prepared from Si(OC2H5)4, Al(OC3H7i)3 and Mg(OC2H5)2 by the sol-gel method. Two different methods were applied for producing fine and homogeneous powders. One is that Si(OC2H5)4 with a lowr rate of hydrolysis was partially hydrolyzed and then Al(OC3H7i)3 and Mg(OC2H5)2 were mixed and reacted. The other is based on the simultaneous hydrolysis of these metal alkoxides using i-C4H9OH which retards the rate of hydrolysis of Al(OC3H7i)3 and Mg(OC2H5)2. It was confirmed that ifne and homogeneous powders were obtained from both methods. Also these powders were calcined at four different temperatures during two hours. X-ray diffraction patterns show only ${\mu}$-cordierite phase at 1000$^{\circ}C$, ${\mu}$-cordierite and ${\alpha}$-cordierite phases at 1100-1200$^{\circ}C$ and ${\alpha}$-cordierite phase at 1300$^{\circ}C$ respectively.

• Bulletin of the Korean Chemical Society
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• 제12권1호
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• pp.97-101
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• 1991

Gas-phase pyrolyses of carbonate esters, ${\alpha}$- and ${\beta}$-hydroxy esters and ${\beta}$-hydroxy ketones have been studied theoretically by the AM1 MO method. Carbonate esters were found to decompose by two types of processes; in the reaction pathway involving an intermediate, the decomposition of the intermediate was rate-limiting, but direct pyrolyses were also possible via a six-membered cyclic transition state in which the methoxy oxygen attacks a hydrogen atom on the ${\beta}$-carbon. The hydroxy esters and ketones were found to decompose in a concerted process involving a six-membered cyclic transition state. Successive methylation on the ${\alpha}$- and ${\gamma}$-carbon led to an increase in the reactivity in agreement with experiments.

• Bulletin of the Korean Chemical Society
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• 제8권3호
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• pp.193-196
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• 1987

The gas phase pyrolyses of eight esters have been studied by MNDO-MO method. In the ethylformate pyrolysis, ${\alpha}$-methylation had a steric releasing effect whereas ${\beta}$-methylation had a steric crowding in the transition state; the latter, however, is over-compensated by a greater electronic repulsion resulting in a net steric releasing effect. Considerations of formal charges and geometrical changes involved in the activation led us to propose a pyrolysis mechanism in which a preequilibrium of acidic proton transfer is followed by the rate-limiting bond polarization of $C_{\alpha}$-O bond in a cyclic transition state.