• Proceedings of the Materials Research Society of Korea Conference
• /
• 1999.05a
• /
• pp.129-129
• /
• 1999

• Journal of Hydrogen and New Energy
• /
• v.19 no.3
• /
• pp.226-231
• /
• 2008

Cu/Fe/$Al_2O_3$ granules with various sizes have been prepared by a combination of sol-gel and oil drop method for the use in sulfur trioxide decomposition, a subcycle in thermochemical sulfur-iodine cycle to split water in the hydrogen and oxygen. The size of composite granules have been mainly changed by the flow-rate of the gel mixture before dropping in the synthesis. The structural properties of the samples were comparable with granule size. In the reaction, the catalytic activity was enhanced by decreasing size in the entire reaction temperature ranges.

• Journal of the Korean Ceramic Society
• /
• v.25 no.3
• /
• pp.225-230
• /
• 1988

The strength and thermal shock resistance of $Al_2O_3-ZrO_2$ composites have been studied. The tetragonal $ZrO_2$ powder containing 1 mol.% $Y_2O_3$ and monoclinic $ZrO_2$ powder were prepared by coprecipitation method and subsequently mixed with $Al_2O_3$ powder and granulated by sieving. Duplex composites were prepared by dry mixing matrix agglomerate with 15 to 30 vol.% of dispersion agglomerate, followed by pressing and sintering at 1$600^{\circ}C$ for1 hr. These $Al_2O_3-ZrO_2$ 2 composites having heterogeneous structure showed improved thermal shock behaviors because of the microcracking and pores in dispersed granules, and compressive stresses around dispersed granules resulting from $ZrO_2$ transformation.

• Applied Chemistry for Engineering
• /
• v.21 no.3
• /
• pp.333-336
• /
• 2010

Fe/$Al_2O_3$ granules with various compositions were prepared by combining sol-gel with oil drop method for Fishcer-Tropsh reaction to produce light olefin from synthesis gas. The granules was characterized and employed as a catalyst in the reaction. The surface area of granules was decreased with increasing Fe concentration. Especially, granule with 1.5 of Al/Fe ratios showed the highest CO conversion. However, the olefin selectivity was hardly affected by Al/Fe ratio. K concentration of granule gave a significant effect on catalytic performance. Initial CO conversion and olefin selectivity were increased with K concentration. However, the catalyst with higher K concentration was deactivated rapidly.

• Journal of Hydrogen and New Energy
• /
• v.19 no.6
• /
• pp.545-551
• /
• 2008

Fe/$Al_2O_3$ composite granules were prepared by combining sol-gel/oil drop method. The shape of granules were mainly determined by composition and concentration of aluminum precursor. The composite granule with the lowest aluminum concentration was synthesized with 0.75M boehmite solution. The prepared granules were tested as a catalyst in the plug-flow reactor for Fischer-Tropsch synthesis. Before the reaction, catalysts were activated by hydrogen reduction and synthesis gas treatment. The activation conditions and aluminum concentration have affected catalytic performance significantly.

• Journal of the Korean Ceramic Society
• /
• v.29 no.4
• /
• pp.283-292
• /
• 1992

Duplex composites such as Y-TZP/Y-TZP-20 wt.% Al2O3 and Y-TZP/Y-TZP- 40 wt.% Al2O3 were made by mixing the sieve-shaked granules followed by isostatic pressing and sintering at 150$0^{\circ}C$ for 1 hour. So Y-TZP became matrix region and Y-TZP-20 wt.% Al2O3 or Y-TZP-40 wt.% Al2O3 became dispersed regions. In these composites, propagating cracks due to thermal shock always run into the dispersed region because these regions act as compressive zone due to low thermal expansion than matrix region. So duplexes having dispersed regions of Y-TZP-40 wt.% Al2O3 showed higher retained strength after thermal shock than matrix only composites because crack propagations were stopped more or less in the dispersed region. But when crack propagations were much more easy than matrix like Y-TZP-20 wt.% Al2O3 region, retained strength was decreased than the matrix only composites despite of the low initial strength.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.8 no.2
• /
• pp.356-364
• /
• 1998

The dependence of green and sintered densities of Zirconia-Toughened Alumina ($ZTA:\;Al_2O_3/\;15\;vol{%}\;ZrO_2$) on the properties of spray-dried granules was studied thoroughly to establish the optimum compaction condition leading to high reproducibility in the light of sintered density. The sphericity, mean size, degree of hollow occurrence and moisture content of spray-dried granules were largely different in between the granule containing binder and the ones with no binder. The effect of these differences in the characteristic of granules on the compaction behavior was examined in terms of the compaction pressure from 80 MPa to 120 MPa 10 MPa increment and the compaction method, i.e., uniaxial and cold isostatic pressing. This work confirmed that the reproducibility of sintered density caused by the variation of granule property could be improved by the optimization of compaction process. The variation of sintered density was controlled within 1 % deviation by compacting the granules under a relatively low pressure of 80 MPa in an uniaxial forming and subsequent cold isostatic pressing at high pressure of 500 MPa.

• Proceedings of the Korea Association of Crystal Growth Conference
• /
• 1997.06a
• /
• pp.13-17
• /
• 1997

The densification of $Al_2$O$_3$/15v/o ZrO$_2$ (Zirconia Toughened Alumina: ZTA) to the 99% of theoretical density was attempted by controlling the processing parameters affecting the each processing step i.e., milling, spray-drying, forming and pressureless sintering. The ZTA processed under the identical conditions showed a large variation in the green and sintered densities, and the mechanical properties. The deviation of 4-point bending strength was more than 100MPa for the ZTA with ~99% of theoretical density. Moreover, the relative green and sintered densities were deviated greatly from the average value. This low reproducibility could be caused by the variation of spray-dried granule properties. Thus, the effect of yield strength and morphology of spray-dried ZTA granule on the green and sintered densities and the mechanical properties needs to be studied in detail. The objective of this work is to fine out the optimum condition of compaction pressure and compaction method depending on the properties of spray-dried granules.

• Journal of Magnetics
• /
• v.3 no.4
• /
• pp.127-133
• /
• 1998

I have overviewed the change in GMR on annealing, in conjunction with the change in microstructure. The Co46Al19O35 granular thin films were annealed at 30$0^{\circ}C$ for various annealing time to change the microstructure. The magnitude of GMR decreases considerably with increasing annealing time, although the size of Co granules estimated from TEM observation show a small change. Parameter fits of magnetization curves and magnetoresistance curves to the Langevin function suggest that large clusters consisting of several small Co granules, which are coupled ferromagnetically, are related with the decrease of GMR on annealing. The temperature dependence of electrical resistivity ($\rho$) shows the relationship of log $\rho$ versus $T^{-1/2}$ for the sample annealed for 10 min., 1 hr. and 6 hrs. However, the sample annealed for 38 hrs. shows the relationship of log $\rho$ versus$ T^{-1/4},$ which represents a significant change in the transport mechanism.

• Journal of the Korean Ceramic Society
• /
• v.38 no.5
• /
• pp.479-484
• /
• 2001

고순도 알루미나 분말에 소결조제로서 MgO를 0ppm 및 500ppm 첨가하여 열분무건조기를 사용하여 준비한 과립을 80$0^{\circ}C$에서 하소를 함으로써 얻어진 과립으로 제작한 소결체의 MgO 첨가량에 따른 미세구조와 꺾임강도에 미치는 영향을 고찰하였다. 또한 시편두께를 50$mu extrm{m}$의 박편으로 가공하여 투광법으로 내부구조도 관찰하였다. MgO를 500ppm 첨가하여 제작한 과립을 180 MPa의 냉간정수압성형성 후 1$600^{\circ}C$에서 소결한 소결체는 상대밀도가 100%에 도달하였고 균일한 결정립성장의 치밀한 미세구조를 나타내었다. MgO를 500ppm 첨가한 시편의 4점 꺾임강도 또한 각 소결온도에서 MgO를 9ppm 첨가한 시편보다 23%-32%정도 높은 강도를 나타내었으며, 특히 소결온도 1$600^{\circ}C$에서는 꺾임강도가 501MPa 그리고 weibull 계수가 20의 고강도이면서 신뢰성이 높은 알루미나 소결체가 얻어졌다. 본 연구에서는 weibull 계수의 값이 높은 시편일수록 내부구조의 결함크기가 작고 이 작은 결함이 시편내부에 균일하게 분포되어 있음을 확인할 수 있었다.