• Journal of the Korean Ceramic Society
• /
• v.23 no.5
• /
• pp.86-92
• /
• 1986

As there is a growing trend to make high quality steel improving production efficiency and utilizing slag as resources the technologies of hot metal pretreatment have been progressed to meet these demands. Although mill scale $Na_2CO_3$ and CaO used as fluxes proved to be excellent agents then can severely corrode refractories such as chamotte and high alumina for torpedo or open ladle car. Thus it was considered necessary to develop new refractories which can endure suchy conditions. Desulfurization fluxes vastly used in POSCO are $CaCO_3$ and CaO Recent trials have been made by testing phenol resin bonded $Al_2O_3-SiC-C$ bricks in torpedo ladle car for hot metal pretreatment. The results showed that the life of this brick became about 1.2 times longer than that of foreign products. And the crushing strength M.O.R corrosion resistance and oxidation resistance were tested.

• Journal of Powder Materials
• /
• v.13 no.6 s.59
• /
• pp.455-461
• /
• 2006

High temperature dielectric constants of the various ceramic materials have been measured using cavity perturbation method. The measurements were applied to refractory, traditional and fine ceramic powder compacts from room temperature to $1200^{\circ}C$. Calibration constant in the equation suggested by Hutcheon et al., was determined from the dielectric constants of reference specimen (teflon and alumina) at room temperature. From these results, informations on the refectory materials were obtained for the microwave kiln design and understanding of the microwave heating effects of ceramics have been improved.

• Journal of the Korean Ceramic Society
• /
• v.17 no.2
• /
• pp.96-100
• /
• 1980

The castable refractory, CaO.$2Al_2O_3$ is a useful alumina cement for iron, steel and cement for iron, steel and cement industries, however it is difficult to produce CaO.$2Al_2O_3$because of its high melting point(180$0^{\circ}C$) and narrow firing range. In this study, the coprecipitation method was used to produce CaO.$2Al_2O_3$ for lower temperature firing . This method involved the titration of mixed solution of calicum and aluminate which extracted from domestic kaolin with $NH4_OH$ solution under blowing $CO_2$ gas into the solution. The coprecipitate and its clacined products were analyzed by X-ray diffraction and DTA. The calcined products fired between 400 and 90$0^{\circ}C$ were amorphous, but at 100$0^{\circ}C$ the coprecipitate was converted into one compound, CaO$2Al_2O_3$. From those experimental results, it was found that we could synthesizze CaO.$2Al_2O_3$ at about 100$0^{\circ}C$ which is lower than conventional firing temperature by around 80$0^{\circ}C$. The refractoriness of this alumina cement was SK 34 and the compressive strength ( 1 day) was about 250kg/$\textrm{cm}^2$.

• Journal of Korea Foundry Society
• /
• v.31 no.5
• /
• pp.267-273
• /
• 2011

Erosion and thermal shock resistance of several refractory materials have been investigated, which are expected to be used as nozzles in a planar flow casting equipment for amorphous alloys. The test was conducted on five materials; graphite, boron nitride, fused silica, alumina and zirconia. Test specimens were preheated and dipped into the melt of carbon steel and amorphous alloys. Some test specimens were rotated to develop high erosion and to shorten the test periods. Fused silica and boron nitride specimens showed the excellent erosion and thermal shock resistance irrespective of the kind of melt and melting atmosphere.

• Journal of the Korean Ceramic Society
• /
• v.38 no.11
• /
• pp.987-992
• /
• 2001

A refractory grade low-cost silicon nitride powder was chemically analyzed, purified, and gas pressure sintered with the sintering additives. As-received powder contained a significant amount of free-Si, 0.72 wt% of Fe, 0.5 wt% of al and 0.31 wt% of Ca. Oxygen and carbon contents of the powder were 3.3 wt% and 0.4 wt%, respectively, and it consisted of 96% of $\beta$-phase and 4% of $\alpha$-phase. After lowering the Fe content and nitriding treatment, the powder was sintered with 6 wt% yttria and 2 wt% alumina for 1 h between 1823 K and 2123 K in order to examine the sintering behavior. Fully dense samples were obtained by sintering at 2123k for 2h. For comparison, a commercially available high-grade powder was also sintered at the same time. The low-cost powder showed much slower densification rate than the high-grade powder. Fully dense sample prepared from the low-cost powder contained a number of coarse grains with a low aspect ratio, and its hardness, fracture toughness, flexural strength and thermal shock resistance were not as good as those of the sample prepared with the high-grade powder.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.23 no.3
• /
• pp.129-134
• /
• 2013

Sapphire wafers are used as an important substrate for the production of blue LED (light emitting diode) and the LED's performance largely depends on the quality of the sapphire single crystals. There are several crystal growth methods for sapphire crystals and Kyropoulos method is an efficient way to grow large diameter and high-quality sapphire single crystals with low dislocation density. During Kyropoulos growth, the convection of molten melt is largely influenced by the hot zone geometry such as crucible shape, heater and refractory arrangements. In this study, CFD (computational fluid dynamics) simulations were performed according to the bottom/side ratios (per unit of the crucible surface area) of heaters. And, based on the results of analysis, the molten alumina flows and remelting phenomena were analyzed.

• Economic and Environmental Geology
• /
• v.15 no.2
• /
• pp.89-102
• /
• 1982

Several mines in Jeonnam produce the ores of having high SK number of refractoriness. Among those for 5 mines, this paper deals with the relationahip between SK number and mineral composition of the ore, and with the genesis of the deposits. 1. Byok-Song and Chon-Un Mine: Mineral compositions of the ores are chiastolite, chloritoid(monoclinic), kaolinite, sericite, diaspore, corundum, and quartz. The ores having SK number of 36 or 37, consist chiefly of chiastolite and diaspore and a little amount of kaolinite, sericite, corundum, chloritoid, and quartz. The ores having SK number of 33 or 34 consist of chloritoid, sericite, kaolinite, chiastolite, and diaspore. With increasing the amount of chloritoid and sericite, and decreasing the amount of diaspore and chiastolite, the SK number of the ores decreases. The deposit, originally high alumina-bearing shale of Chon-Un San formation, seems to be formed by contact metamorphism(forming of chiastolite), regional metamorphism(forming of monoclinic chloritoid), and hydrothermal replacement(forming of large crystal of diaspore veinlets). 2. Song-Sauk Mine: Mineral compositions of the ores are chiefly pyrophyllite and quartz and a little amount of kaolinite, dickite, diaspore, and pyrite. Many spherical inclusions containing in pyrophyllite deposits, consist chiefly of diaspore and kaolinite, The inclusions have the high SK number of 38. Amount of spherical inclusions is about 5 % to the whole pyrophyllite ores. The SK number of other pyrophyllite ore is less than 32. Quartz and pyrite are chief minerals lowering the SK number of the ore. The deposits have been formed by hydrothermal processes by replacing the siliceous tuff of Mesozoic age. Spherical inclusions consisting of diaspore and kaolinite, show the selective replacement of hydrothermal solutions to the materials of feldspar in tuff. 3. Seung-San Mine: Mineral compositions of the ores are chiefly kaolinite, dickite, diaspore, and quartz. But some part of the mine consists of alunite deposits. The ores having SK number of 35 or higher consist chiefly of kaolinite and diaspore and a little amount of quartz. With increasing the amount of quartz and decresing the amount of diaspore, the SK number of the ore decreases. The deposits have been formed by hydrothermal processes by replacing the siliceous tuff and quartz porphyry. 4. Wan-Do Mine: Mineral compositions of the ores are chiefly pyrophyllite and quartz. But some ore contains a little amount of diaspore, kaolinite, pyrite, and chloritoid. The ores having high SK number of 36 consist chiefly of diaspore and pyrophyllite. Pyrophyllite ore has a SK number of 32 or lower. Amount of quartz and pyrite decreases the SK number of ores in this mine. Rhyolite was replaced by the action of hydrothermal solutions forming the pyrophyllite deposits.