• Journal of the Korean Ceramic Society
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• v.40 no.7
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• pp.632-636
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• 2003

To prepare the alumina cement free vibrated alumina castable, $\rho$-alumina is employed as a binder material, and nano-sized clay is added to enhance the curing strength and give thixotropic behavior. The rheological behavior of matrix of castable is controlled by investigating the influences of ultrafines, $\rho$-alumina, and nano-sized clay on the viscosity of matrix. The microsilica and ultrafine alumina were added 3 wt% and 4 wt%, respectively to the matrix, which showed that the viscosities tends to be lowest values. The rheological property of the matrix is well established by adding $\rho$-alumina as 8 wt% and clay as 4 wt%. The thixotropic behavior of the $\rho$-alumina bonded castable was appeared by introducing nano-sized clay into the matrix and adjusting the pH near to the PZC of the clay suspension.

• Proceedings of the Korean Ceranic Society Conference
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• 2003.10a
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• pp.141.1-141
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• 2003

• Journal of the Korean Ceramic Society
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• v.40 no.10
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• pp.1015-1020
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• 2003

The Corrosion behavior of the matrix of the $\rho$-alumina bonded alumina vibrated castable was, on the basis of Jabsen's theory, elucidated by use of the Kingery's reaction mechanism. Corrosion of the matrix during induction period was controlled by the molecular diffusion. The temperature dependence of activation process is well established by the Arrhenius plots. The difference of Ca concentration between slag and interface is 23.2%, which causes a driving force of the materials transfer. The extent of the corrosion of the matrix is more deeper than that of the sintered mullite, but the corrosion mechanism can be well employed as the reaction mechanism proposed by the Kingery. The life time of the castable may be well estimated by the corrosion mechanism of Kingery.

• Journal of the Korean Ceramic Society
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• v.40 no.8
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• pp.791-797
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• 2003

The special binding mechanism developed provides higher density, lower porosity and higher strengths compared with conventional castables. $\rho$-alumina was employed as a binder materials and nano-sized clay colloidal was added to enhance the drying strength preparing for the alumina vibrated castable. Lower water requirement for casting results in a denser product. The mechanical properties with dimensional stability and corrosion resistance behaviors have been improved by controlling the matrix compositions of the castable. The modulus of rupture and compressive strength after heat treatment at 150$0^{\circ}C$ are 92.34 kgf/$\textrm{cm}^2$ and 370 kgf/$\textrm{cm}^2$ respectively. The activation energy of mullite formation is 11.47 kcal/mol.

• Proceedings of the Materials Research Society of Korea Conference
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• 2003.03a
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• pp.196-196
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• 2003

• Proceedings of the Korean Ceranic Society Conference
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• 2002.10a
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• pp.155.2-155
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• 2002

• Journal of the Korean Ceramic Society
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• v.43 no.12 s.295
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• pp.859-864
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• 2006

For the pressure compaction process of the ceramic powder, the green density is very different with both the ceramic body shape and the processing conditions. The density difference cause non-uniform shrinkages and deformations, and make cracks in the sintered ceramics. In this paper, Material properties of the alumina powder mixed with binder and the friction coefficient between the powder and the tool set were determined through the simple compaction experiments: Also the powder flow characteristics were simulated and the green density was analyzed during the powder compaction process with Finite Element Method (FEM). The results show that the density distributions of the green body were improved at the optimized processing condition and both the possibility of the farming crack generation and rho deformation of the sintered Alumina body were reduced.

• Bulletin of the Korean Chemical Society
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• v.23 no.6
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• pp.803-807
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• 2002

The conversion of dimethyl ether(DME) has been carried out over $\gamma-alumina$, silica-alumina, and modified $\gamma-aluminal$ catalysts. Especially, the water effect has been investigated on purpose to develop a suitable catalyst for one-step synthesis of DME from $CO_2$ hydrgenation, The $\gamma-Al_2O_3$ modified with 1 wt% silica is more active and less deactivated by water than unmodified one. $CO_2has$ no effect on catalytic dehydration of methanol to DME.

• Journal of the Korean Ceramic Society
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• v.39 no.3
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• pp.272-277
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• 2002

Aluminum nitride (AlN) powders and whiskers were synthesized by a modified carbothermal reduction and nitridation where a ($NH_4)[Al(ethylenediaminetetraacetate)]{\cdot}2H_2O$ complex is used as precursor. The AlN powders were obtained by calcining the complex without mixing any carbon source under a flow of nitrogen in the temperature range 1200∼1500$^{\circ}$C and then burning out the residual carbon. The nitridation process was investigated by $^{27}Al$ magic-angle spinning (MAS) unclear magnetic resonance, infrared spectroscopy and X-ray diffraction. The complex is pyrolyzed, converted to ${\rho}$- and ${\gamma}$- alumina and then nitridated to AlN without ${\gamma}-{\alpha}$ alumina transition. The morphology of ${\gamma}$-alumina, when it was converted to AlN, was retained, strongly indicating that ${\gamma}$-alumina is converted to AlN through solid-state $AlO_xN_y$, not through gaseous intermediates such as aluminum and aluminaum suboxides. AlN whiskers were obtained, when a (0001) sapphire was used as a catalyst.

• Journal of the Korean institute of surface engineering
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• v.32 no.1
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• pp.3-9
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• 1999

Pt thin film of about 7000$\AA$ thickness was deposited on the alumina substrate using DC Magnetron Sputter and the characteristics of the film for temperature sensor were investigated. When film of about 7000$\AA$ thickness was deposited at working gas pressure of $2.0{\times}10^{-3}$torr, sputtering power of 50W, substrate temperature of $350^{\circ}C$(Ts), sheet resistance(Rs), resistivity($\rho$) and temperature coefficient of resistivity(TCR) of the film were respectively 0.39$\Omega$/$\square$, 27.60$\mu\Omega$-cm and $3350 ppm/^{\circ}C$. When the film was annealed at $1000^{\circ}C$ for 240min in hydrogen ambient, Rs, $\rho$ and TCR were respectively 0.236$\Omega$/$\square$, 15.18$\mu\Omega$-cm and 3716 ppm/$3716 ppm/^{\circ}C$. When working gas of 15sccm oxygen and 100sccm Argon were used, Rs, $\rho$ and TCR were respectively 0.335$\Omega$/$\square$, 22.45$\mu\Omega$-cm and $3427 ppm/^{\circ}C$. When the film was annealed at $1000^{\circ}C$ for 240min, Rs, $\rho$and TCR were respectively 0.224/$\Omega$$\square$, 14$\mu\Omega$-cm and $3760 ppm/^{\circ}C$ and the characteristics of the film were much improved.