• Journal of the Korean Society for Heat Treatment
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• v.31 no.6
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• pp.300-306
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• 2018

In the present study we proposed new equations to predict the liquidus temperature curve for hypoeutectic Al-Si-Cu-Mg alloy. A thermodynamic simulation was carried out to calculate the liquidus temperature, eutectic temperature and eutectic Si concentration with different Si, Cu, and Mg contents in hypoeutectic Al-Si alloys. Regressed equations were derived using the thermodynamic simulation results by multiple regression analysis. The proposed equations were compared with the equations reported previously by other researchers and agreed better with the experimental data. The addition of Cu and Mg lowered the eutectic temperature. The eutectic Si concentration was decreased by adding Cu whereas that was increased by adding Mg. Al-Si binary phase diagram was successfully predicted with a consideration of the effect of Cu and Mg addition by using the proposed equations.

• 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.

• Journal of Technologic Dentistry
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• v.23 no.1
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• pp.9-19
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• 2001

Microstructure and phase transformation of Ti-Ni-Cu alloy powders produced by using attrition milling method were studied. Mixed powders of Ti-(50-X)Ni-XCu ($X=0{\sim}20$ at%) in composition range were mechanically alloyed for maximum 20 hours by using SUS 1/4" ball in argon atmosphere. Ball to powder ratio was 50: 1 and impeller speed was 350rpm. Mechanically alloyed with attrition millimg method. powder was heat treated at the temperature up to $850^{\circ}C$ for 1 hour in the $10^{-6}$ torr vacuum. Ti-Ni-Cu alloy powders have been fabricated by attrition milling method. and then phase transformation behaviours and microstructual properties of the alloy powders were investigated to assist in improving the the high damping capacity of Ti-Ni-Cu shape memory alloy powders. The results obtained are as follows: 1. After heat treating of fully mechanically alloyed powder at $850^{\circ}C$ for 1hour. most of the B2 and B 19' phases was formed and $TiNi_3$ were coexisted. 2. The B 19' martensite were formed in Ti-Ni-Cu alloy powders whose Cu-content is less than 5a/o. where as the B19 martensite in those whose Cu-content is more than 10at%. 3. The powders of as-milled Ti-Ni-Cu alloys whose Cu-contents is less than 5at% are amorphous. whereas those of as-milled Ti-Ni-Cu alloys whose Cu-content is more than 10at% are crystalline. This means that Cu addition tends to suppress amorphization of Ti-Ni alloy powders.

• Journal of the Korean Ceramic Society
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• v.49 no.6
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• pp.528-534
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• 2012

In this study, the densification behavior and microstructural evolution of CuO were examined when this material was sintered at different temperatures in $O_2$, air and Ar atmospheres. The CuO samples maintained their phases even after prolonged sintering at $900-1100^{\circ}C$ in an oxygen atmosphere. When sintering in air, the densification was faster than it was when sintering in oxygen. However, when the samples were sintered at $1100^{\circ}C$, large pores were observed in the sample due to the phase transformation from CuO to $Cu_2O$ which accompanies the generation of oxygen gas. The pore channels in the sample became narrower as the sintering time increased, eventually undergoing a Rayleigh breakup and forming discrete isolated pores. On the other hand, CuO sintering in Ar did not contribute to the densification, as all CuO samples underwent a phase transformation to $Cu_2O$ during the heating process.

• Journal of the Korean Ceramic Society
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• v.41 no.2
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• pp.111-117
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• 2004

3Y-TZP containing 0.3∼1.2 wt% of $Al_2$O$_3$ was prepared by slip-casting after attrition milling. The specimen was sintered at 1390∼151$0^{\circ}C$ and mechanical characterization and microstructure analysis were conducted. Monoclinic content of the specimen was calculated by XRD. The apparent density of specimen increased with increasing sintering temperature. While above 1470%, the formation of m-ZrO$_2$ degraded the density. The microhardness of specimen decreased with temperature because monoclinic phase increased wit the grain growth. The specimen containing $Al_2$O$_3$ below 0.9 wt% sintered at 143$0^{\circ}C$ showed the highest microhardness of 1360 Hv.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.07b
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• pp.1218-1221
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• 2004

Bi2212 superconducting thin films fabricated by using the ion Beam Sputtering Method. As a result, although the composition of Bi2212 was set up, the phase of Bi2201, Bi2212 and Bi2223 was formed. The formation area of these stable phases is indicated as inclined line in the direction of the right lower end from the Arrhenius plot of the substrate temperature-oxidation gas pressure, and are distributed in very small area. The activation energy for the phase transformation from the Bi2201 to the Bi2212 is estimated in terms of the Avrami equation.

• Journal of Powder Materials
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• v.14 no.2 s.61
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• pp.145-149
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• 2007

Nanocrystalline transient aluminas (${\gamma}$-alumina) were coated on core particles (${\gamma}$-alumina) by a carbonate precipitation and thermal-assisted combustion, which is environmentally friend. The ammonium aluminum carbonate hydroxide (AACH) as a precursor for coating of transient aluminas was produced from precipitation reaction of ammonium aluminum sulfate and ammonium hydrogen carbonate. The crystalline size and morphology of the synthetic, AACH, were greatly dependent on pH and temperature. AACH with a size of 5 nm was coated on the core alumina particle at pH 9. whereas rod shape and large agglomerates were coated at pH 8 and 11, respectively. The AACH was tightly bonded coated on the core particle due to formation of surface complexes by the adsorption of carbonates, hydroxyl and ammonia groups on the surface of the core alumina powder. The synthetic precursor successfully converted to amorphous- and ${\gamma}$-alumina phase at low temperature through decomposition of surface complexes and thermal-assisted phase transformation.

• Korean Journal of Materials Research
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• v.15 no.7
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• pp.435-438
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• 2005

Single phase $Zn_4Sb_3$ with $98.5\%$ of theoretical density was successfully produced by direct hot pressing of elemental powders containing $1.2 at\%$ excess Zn for compensating the evaporation during the process. Temperature dependences of thermoelectric properties were investigated from 4 K to 300 K. Seebeck coefficient, electrical conductivity, thermal conductivity as well as thermoelectric figure of merit showed the discontinuity in variation at 242K, indicating the $\alpha-\beta$, phase transformation. Interestingly, it was found that lattice thermal conductivity by phonons is dominant in total thermal conductivity of $\alpha-\beta$. Therefore, it is expected that thermoelectric properties can be improved by reduction of lattice thermal conductivity inducing lattice scattering centers by doping and solid solution.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.07b
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• pp.719-722
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• 2002

The Displacement current measurement system used in this experiment because detecting the dynamic behavior of monolayers at the air-water interface is possible. It basically consists of a film balance, a pair of electrodes connected to each other through a sensitive ammeter. Here, one electrode is suspended in air and the other electrode is placed in the water. PBLG phase transformation measured by Maxwell-displacement-current-measurement method in surface of the water. Measured (surface pressure, displacement current and dipole moment) of monolayers of PBLG on the water surface. We measured displacement current that occur when changed temperature. Could know that displacement current is proportional in increase of temperature and great as experiment result.

• Fibers and Polymers
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• v.5 no.2
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• pp.105-109
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• 2004

The synthesis of titanium dioxide nanofibers with 200-300nm diameter was presented. The new inorganic-organic hybrid nanofibers were prepared by sol-gel processing and electrospinning technique using a viscous solution of titanium isopropoxide (TiP)/poly(vinyl acetate) (PVAc). Pure titanium dioxide nanofibers were obtained by high temperature calcination of the inorganic-organic composite fibers. SEM, FT-IR, and WAXD techniques were employed to characterize these nanofibers. The titanium dioxide nanostructured fibers have rougher surface and smaller diameter compare with PVAc/TiP composite nanofibers. The anatase to rutile phase transformation occurred when the calcination temperature was increased from $600^{\circ}C$ to $1000^{\circ}C$.