• Korean Journal of Materials Research
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• v.14 no.10
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• pp.696-700
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• 2004

The reduction behavior of $Al_{2}O_3/CuO$ powder mixtures, prepared from $Al_{2}O_3/CuO$ or $Al_{2}O_3/Cu-nitrate$, was investigated by using thermogravimetry and hygrometry. The powder characteristics were examined by BET, XRD and TEM. Also, the influence of powder characteristics on the microstructure and properties of hot-pressed composites was analyzed. The formation mechanism of nano-sized Cu dispersions was explained based on the powder characteristics and reduction kinetics of oxide powders. In addition, the dependence of the microstructure and mechanical properties of hot-pressed composites on powder characteristics is discussed in terms of the initial size and distribution of Cu particles. The practical implication of these results is that an optimum processing condition for the design of homogeneous microstructure and required properties can be established.

• Korean Journal of Materials Research
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• v.12 no.2
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• pp.153-159
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• 2002

The co-deposited behavior was investigated under varied bath compositions and current densities from Watt Ni plating bath containing Al and A1$_2$O$_3$powders. For single-particle bath, Al and A1$_2$O$_3$particles were agglomerated. The area percentage of A1$_2$O$_3$on plating surface decreased with increasing the current density, while that of Al on plating surface increased. On the other hand, in case of double-particle bath with 1.25g/$\ell$ of Al and 5.0g/$\ell$ of A1$_2$O$_3$5g, the area percentage of Ni-Al-A1$_2$O$_3$increased with increasing current density and the surface morphology was fine without agglomeration. Intermetallic compounds such as $\gamma$'and $\gamma$+$\gamma$' phases appeared when the co-deposited film was annealed.

• Journal of the Korean Ceramic Society
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• v.39 no.7
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• pp.704-709
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• 2002

To improve the mechanical properties of $Al_2$O$_3$/ZrO$_2$composites, the homogeneous dispersion of ultra low size ZrO$_2$ particles in $Al_2$O$_3$ceramics have been controlled by coprecipitation method. In case of mechanical mixing of ZrO$_2$ powders with $Al_2$O$_3$, homogeneous dispersion and controlling the ZrO$_2$ size were relatively difficult due to high sintering temperature. So nanosized Zr hydroxide was coprecipitated from ZrOCl$_2$/Y(NO$_3$)$_3$ solution with commercial sub-micron sized $\alpha$-alumina (Sumitomo : AES-11(0.4 ${\mu}{\textrm}{m}$)) and high purity ultra low sized $\alpha$-alumina (Taimei Chemical (0.22 ${\mu}{\textrm}{m}$)) for low temperature sintering. By this partial coprecipitation method, relatively low sized ZrO$_2$ dispersion in $Al_2$O$_3$/ZrO$_2$ composites was achieved at 150$0^{\circ}C$-1$600^{\circ}C$ of sintering temperature range and their mechanical properties were measured.

• Composites Research
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• v.16 no.3
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• pp.75-84
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• 2003

The purpose of this study is to investigate the wear properties of Saffil/Al, Saffil/A12O3/Al and Saffil/SiC/Al hybrid metal matrix composites fabricated by squeeze casting method. Wear tests were done on a pin-on-disk friction and wear tester under both dry and lubricated conditions. The wear properties of the three composites were evaluated in many respects. The effects of Saffil fibers, $\textrm{Al}_2\textrm{O}_3$ particles and SiC particles on the wear behavior of the composites were investigated. Wear mechanisms were analyzed by observing the worn surfaces of the composites. The variation of coefficient of friction(COF) during the wear process was recorded by using a computer. Under dry sliding condition, Saffil/SiC/Al showed the best wear resistance under high temperature and high load, while the wear resistances of Saffil/Al and Saffi1/$\textrm{Al}_2\textrm{O}_3$/Al were very similar. Under dry sliding condition, the dominant wear mechanism was abrasive wear under mild load and room temperature, and the dominant wear mechanism changed to adhesive wear as load or temperature increased. Molten wear occurred at high temperature. Compared with the dry sliding condition, all three composites showed excellent wear resistance when lubricated by liquid paraffin. Under lubricated condition, Saffil/Al showed the best wear resistance among them, and its COF value was the smallest. The dominant wear mechanism of the composites under lubricated condition was microploughing, but microcracking also occurred to them to different extents.

• The Korean Journal of Ceramics
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• v.5 no.4
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• pp.390-394
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• 1999

Al2O3 particles were dispersed into carbon fiber reinforced epoxy composites to fabricate hybrid epoxy based composites. Interface behavior and mechanical properties of these hybrid composites were studied at room and liquid nitrogen temperature and liquid nitrogen temperature and the results were compared with the those of carbon fiber reinforced composites to investigate their applicability at room and cryogenic temperature. Young's modulus in-perpendicular to fiber direction and interlaminar shear strength at room temperature and the thermal contraction down to cryhogenic temperature were improved significantly by the addition of AL2O3 filler into the epoxy matrix. The effect of Al2O3 particle addition on mechanical properties were discussed.

• Journal of the Korean institute of surface engineering
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• v.43 no.4
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• pp.165-169
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• 2010

$Ni-Al_2O_3$ nanocomposite coatings were fabricated by conventional electrodeposition technique using nickel sulfamate bath. Effect of plating parameters on electrodeposition of $Ni-Al_2O_3$ nanocomposite were studied. The properties of the nano composite were investigated by using SEM, XRD, and Vicker's microhardness test. The results demonstrated that $Al_2O_3$ incorporation in the composite coatings was found to be increased by increasing stir rate and $Al_2O_3$ content in plating bath. Microhardness of the composite coatings was also increased with increasing content of the nano particles in the plating bath. The surface morphologies of the nanocomposite coatings were found to be varied with varying pH, current densities as well as alumina content in the plating bath.

• Journal of Welding and Joining
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• v.11 no.1
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• pp.62-72
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• 1993

Recently there is an increased interest in joining of ceramics to metals and brazing now an accepted method of joining for a wide variety of ceramic to metal combination. The present research work is aimed at establishing the basis of the metal-ceramic joining of $Al_{2}$O$_{3}$ to STS 304 with using Cu-7.5wt% Zr insert metals. Also the microstructures of the brazed joints were observed by using optical microscope and SEM and the reaction products were analyzed by using EDX, WDX and XRD. As a result, the following findings were obtained. The reaction layers of the brazed joints of $Al_{2}$O$_{3}$ to STS 304 are composed of four layers at the bonded interlayer. Double reaction layers are formed at the interface of $Al_{2}$O$_{3}$ insert metal. Layer I was composed of ZrO$_{2}$ particles, Fe-Cr-Ni compounds in Cu matrix, while layer II ZrO$_{2}$ band phase containing Fe-Cr-Ni compounds.

• Bulletin of the Korean Chemical Society
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• v.33 no.2
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• pp.387-392
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• 2012

A series of Pd-based catalysts were prepared and examined for the amination of 2,6-dimethylphenol in a fixedbed reactor. The best results were obtained for Pd/$Al_2O_3$-BaO with a conversion of 99.89% and a selectivity of 91.16%. These catalysts were characterized using BET, XRD, XPS, TEM and $NH_3$-TPD. Doped BaO not only improved the dispersion of the Pd particles but also decreased the acidity of the catalyst, which remarkably enhanced the selectivity and stability of the catalyst. The generality of Pd/$Al_2O_3$-BaO for this kind of reaction was demonstrated by catalytic aminations of o- and p-alkyl phenols.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.3 no.2
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• pp.185-201
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• 1993

The objectives of this study are to identify the physical, chemical and microstructural properties of coal fly ash and to increase the industrial use of coal fly ash. Experimental results show that 3 major constituents of coal fly ash are $SiO_2$, $Al_2O_3$ and coal fly ash includes the crystalline of Quartz and Mullite. Coal fly ash are classified into 7 groups based on the type of microstructure. Cenosphere is divided into floater and dry separated cenosphere which are consist mainly of $SiO_2$ and $Al_2O_3$. Cenosphere segregations are formed by adsorption and neck growth of the smaller sized cenosphere particles on the condition of the high temperature and air pressure.

• The Journal of Advanced Prosthodontics
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• v.10 no.1
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• pp.43-49
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• 2018

PURPOSE. The purpose of this in vitro study is to examine the effects of a nano-structured alumina coating on the adhesion between resin cements and zirconia ceramics using a four-point bending test. MATERIALS AND METHODS. 100 pairs of zirconium bar specimens were prepared with dimensions of $25mm{\times}2mm{\times}5mm$ and cementation surfaces of $5mm{\times}2mm$. The samples were divided into 5 groups of 20 pairs each. The groups are as follows: Group I (C) - Control with no surface modification, Group II (APA) - airborne-particle-abrasion with $110{\mu}m$ high-purity aluminum oxide ($Al_2O_3$) particles, Group III (ROC) - airborne-particle-abrasion with $110{\mu}m$ silica modified aluminum oxide ($Al_2O_3+SiO_2$) particles, Group IV (TCS) - tribochemical silica coated with $Al_2O_3$ particles, and Group V (AlC) - nano alumina coating. The surface modifications were assessed on two samples selected from each group by atomic force microscopy and scanning electron microscopy. The samples were cemented with two different self-adhesive resin cements. The bending bond strength was evaluated by mechanical testing. RESULTS. According to the ANOVA results, surface treatments, different cement types, and their interactions were statistically significant (P<.05). The highest flexural bond strengths were obtained in nano-structured alumina coated zirconia surfaces (50.4 MPa) and the lowest values were obtained in the control group (12.00 MPa), both of which were cemented using a self-adhesive resin cement. CONCLUSION. The surface modifications tested in the current study affected the surface roughness and flexural bond strength of zirconia. The nano alumina coating method significantly increased the flexural bond strength of zirconia ceramics.