• Journal of Welding and Joining
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• v.18 no.3
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• pp.51-59
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• 2000

Sink roll has been used in molten 55%Al-Zn alloy bath of continuous galvanizing line for sinking and stabilizing working steel strip in molten metal bath. In the process, the sink roll body inevitably build up dross compounds and pitting on the sink roll surface during 55%Al-Zn alloy coated strip production, and the life time of the sink roll is shorten by build up dross compounds and pitting. The present study examined the application of thermally sprayed ceramic coatings method on sink roll body for improving erosion resistance at molten 55% Al-Zn pool. In this experiment, the stainless steels such as STS 316L and STS 430F were used as the substrate materials. The CoNiCr and WE-Co powder were selected as bond coating materials. Moreover $Al_2O_3-ZrO_2-SiO_2 and ZrO_2-SiO_2$ powders selected as the top coating materials. Appearances of the specimens before and after dipping to molten 55%Al-Zn pool were compared and analyzed. As a result of this study, STS430F of substrate, WC-Co of bond spray coatings, $ZrO_2-SiO_2$ power of top spray coatings is the best quality in erosion resistance test at molten 55%Al-Zn pool

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.18 no.1
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• pp.5-9
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• 2008

Cordierite has a very low thermal expansion coefficient, but has problem that it has a weak mechanical strength and is apt to be attacked by acid such as sulfur for using as a diesel particulate filter support. The physical properties of $ZrTiO_4$ modified with $SiO_2,\;Al_2O_3$, MoOx, $Cr_2O_3\;and\;Nb_2O_5$ were investigated with XRD, SEM, UTM and thermal expansion, etc. in this paper. $ZrTiO_4$ powder was synthesized as a monoclinic structure with processes that starting materials of $TiO_2\;and\;ZrO_2$ were mixed with ball mill and calcined above $1240^{\circ}C$ for 3 hr. Additive modified $ZrTiO_4$ specimens for flexural strength and thermal expansion measurement were obtained by mixing $ZrTiO_4$ powder with additives, pressing and firing at $1300^{\circ}C$ for 3 hr. The porosity of additive modified $ZrTiO_4$ decreased monotonically with increasing additive content by 5 wt% regardless of additive types and saturated for further increase of additive by 10wt. The flexural strength of $Al_2O_3$ (5, 10 wt%) modified $ZrTiO_4$ shows a large increase, but that of other additives modified $ZrTiO_4$ decreased. The thermal expansion coefficient of additive modified $ZrTiO_4$ except $Nb_2O_5$ decreased continuously with the content of additive. In particular, the lowest thermal expansion coefficient of $ZrTiO_4$ was obtained for the additive of $SiO_2$.

• Journal of the Korean Ceramic Society
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• v.31 no.3
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• pp.337-345
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• 1994

The reaction-sintered alumina and zirconia-alumina ceramics having low firing shrinkage were prepared from the Al/Al2O3 or Al/ZrO2(Ca-PSZ) powder mixtures via the attrition milling. And in this milling process the effect of the characteristics of used powders was investigated. Attrition milling was much more effective in reducing the particle size of ceramic/metal mixed powders than ball milling. Powder mixtures of flake-type Al with coarse alumina was much more effectively comminuted by the attrition milling than the mixtures of globular-type Al with coarse alumina powders. And coarse alumina than fine alumina was much more beneficial in cutting and reducing the ductile Al particles. In the contrary to Al/Al2O3 powder mixtures, Al/ZrO2 powder mixtures was not effectively comminutd. But whether using the alumina ball media or attrition milled with Al2O3 powder rather than Al, the milling efficiency was much more increased.

• Journal of the Korean Ceramic Society
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• v.37 no.3
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• pp.211-218
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• 2000

The attrition-milled powder mixtures of Al and Al2O3 were oxidized below 140$0^{\circ}C$ for 1 hr and post-sintered at 150$0^{\circ}C$ and 1$600^{\circ}C$ for 2 hr. During attrition milling, ZrO2 was added to the system by grinding effect of ZrO2 balls. The average particle size of the powder mixtures was decreased by the attrition milling as the aluminum content decrease. Above 120$0^{\circ}C$, sintering behaviro was observed on the fine Al2O3 particles resulted from the oxidation of Al. The specimens heat-treated at 140$0^{\circ}C$ for 1 hr showed the bending strength of 166 MPa and hardness of 220 MPa. The specimens post-sintered at 1$600^{\circ}C$ for 2hr had a linear shrinkage of 9~12% and a relative density of about 95%. After the post-sintering, the specimens having 55 vol% Al content revealed the bending strength of 513 MPa and hardness of 718 MPa. The Weibull modulus to the bending strength was about 16.

• Journal of Korea Foundry Society
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• v.34 no.2
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• pp.60-66
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• 2014

A Zr-based amorphous alloy specimen was produced by vacuum die casting process. The salt spray test was carried out using the specimens in the as-cast, $Al_2O_3$ and $ZrO_2$ particle blasted state. Using these specimens, the SEM-EDX and XRD analyses, DSC measurement and bending strength test were conducted. After the salt spray test, the specimens were not experienced phase change and thermal characteristics of the alloys were remained unchanged. In the as-cast specimen, corrosion products were not observed. However, in the $Al_2O_3$ particle blasted specimen, pitting corrosion occurred and the detected corrosion products were $ZrCl_2$ and $NaZrO_3$. Due to the salt spray test, bending strength of the $Al_2O_3$ blasted specimens showed about 100 MPa lower strength than the other specimens. The bending fracture surface was vein pattern which was shown typically in the amorphous alloys.

• Proceedings of the KIEE Conference
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• 2000.07c
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• pp.1474-1476
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• 2000

The mechanical and electrical properties of the hot-pressed and annealed $\beta$-Sic-$ZrB_2$ electroconductive ceramic composites were investigated as function of the liquid forming additives of $Al_{2}O_{3}+Y_{2}O_{3}$. Phase analysis of composites by XRD revealed $\alpha$-SiC(6H), $ZrB_2$, and YAG($Al_{5}Y_{3}O_{12}$). The relative density of composites were increased with increasing $Al_{2}O_{3}+Y_{2}O_{3}$ contents. The flexural strength showed the highest value of 390.6MPa for composites added with 20wt% $Al_{2}O_{3}+Y_{2}O_{3}$ additives at room temperature. Owing to crack deflection, crack bridging. phase transition and YAG of fracture toughness mechanism. the fracture toughness showed the highest value of 6.3MPa${\cdot}m^{1/2}$ for composites added with 24wt% $Al_{2}O_{3}+Y_{2}O_{3}$ additives at room temperature. The electrical resistivity of the composites was all positive temperature coefficient resistance (PTCR) in the temperature range of 25$^{\circ}C$ to 900$^{\circ}C$.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.6 no.2
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• pp.275-285
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• 1996

The effect of heat-treatment on catalytic crystallization in $LI_2O-Al_2O_3-SiO_2$ glass system over its glass transition temperature was investigated. Glass composition $4Li_2O{cdot}22AL_2O_3{cdot}66SiO_2{cdot}2TiO_2{cdot}2.5ZrO_2{cdot}1.5P_2O_5{cdot}1.0Na_2O{cdot}1.0As_2O_3$ (wt%) was selected and heat-treated at different heating conditions to obtain transparent glass-ceramic. Nucleation and crystallization behaviour of this composition were estimated by differential thermal analysis (DTA) and X-ray diffractometer (XRD) and its thermal expansion coefficients were measured by Dilatometer. As a result, glass transition temperature was $730^{\circ}C$ and two maximum nucleation temperatures were estimated at $730^{\circ}C$ and 82$0^{\circ}C$ using JMA(Johson-Mehl-Avrami) equation by DTA. $ZrTiO_4$ $\beta$-Quartz solid solution and $\beta$-Spodumene crystals were identified by XRD. The optimum crystallization temperature was 92$0^{\circ}C$ and three step heating schedule was expected to be useful to obtain transparent glass-ceramic.

• Bulletin of the Korean Chemical Society
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• v.31 no.11
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• pp.3283-3290
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• 2010

The gas-phase dehydration of glycerol to acrolein was carried out over 10 wt % HSiW catalysts supported on different supports, viz. $\gamma-Al_2O_3$, $SiO_2-Al_2O_3$, $TiO_2$, $ZrO_2$, $SiO_2$, AC, $CeO_2$ and MgO. The same reaction was also conducted over each support without HSiW for comparison. Several characterization techniques, $N_2$-physisorption, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), the temperature-programmed desorption of ammonia ($NH_3$-TPD), temperature-programmed oxidation (TPO) with mass spectroscopy and CHNS analysis were employed to characterize the catalysts. The glycerol conversion generally increased with increasing amount of acid sites. Ceria showed the highest 1-hydroxyacetone selectivity at $315^{\circ}C$ among the various metal oxides. The supported HSiW catalyst showed superior catalytic activity to that of the corresponding support. Among the supported HSiW catalysts, HSiW/$ZrO_2$ and HSiW/$SiO_2-Al_2O_3$ showed the highest acrolein selectivity. In the case of HSiW/$ZrO_2$, the initial catalytic activity was recovered after the removal of the accumulated carbon species at $550^{\circ}C$ in the presence of oxygen.

• Journal of the Korean Institute of Telematics and Electronics
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• v.27 no.6
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• pp.886-894
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• 1990

Sinterbility, microstructure, mechenical and electrical properties of yttriastabilized zirkconiz (92 mole % ZrO2 + 8 mole % Y2O3) doped with 0.5 mole % SiO2 and 0-2.O mole% Al2O3 were studied as a functin of Al2O3 addition. Sintered density increased with increasing Al2O3 addition up to o.5 mole%but decreased up to 1.0mole% Al2O3. Vickers hardness is proportional to sintered density. The specimen added 0.5mole% Al2O3 and 0.5mole% SiO2 exhibited a maximum conductivity. And the specimen added 0.5 mole % Al2O3 and 0.5 mole% SiO2 was measured a maximum electromotive force for a characteristics of oxyzen partial pressure.

• Bulletin of the Korean Chemical Society
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• v.31 no.1
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• pp.120-124
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• 2010

Monometallic, bimetallic and trimetallic particles consisting of different weight compositions of Pt-Pd-Rh over pure alumina wash coats have been synthesized and their catalytic performance on methane conversion was studied from 150 to $600^{\circ}C$. Different catalyst formulations with variable Pt, Pd and Rh contents for bimetallic and trimetallic systems were tried and $Pt_{(1.5)}Rh_{(0.3)}/Al_2O_3$ and $Pt_{(1.0)}Pd_{(1.0)}Rh_{(0.3)}/Al_2O_3$ shows low $T_{50}$ and $T_{90}$ temperatures. Bimetallic and trimetallic particle synergism acts as three way catalysts and therefore, all the catalysts show 100% methane conversion. The effect of supports such as $ZrO_2$ and $TiO_2$ on methane combustion was investigated; from $T_{50}$ and $T_{90}$ results both $Al_2O_3$ and $ZrO_2$ are suitable supports for low temperature methane combustion.