• Journal of the Korean Ceramic Society
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• v.29 no.6
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• pp.463-470
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• 1992

Corundum single crystals were grown in cryolite flux with the composition of Na3AlF6:Al2O3=80:20 wt%. This mixture was melted at 115$0^{\circ}C$, followed by slow cooling at a rate of 2$^{\circ}C$/hr to 96$0^{\circ}C$. And by adding of La2O3 to the flux, the change of crystal forms were observed. Crystal forms of corundum grown in cryolite flux had the habits of hexagonal plate which consist of well developed {0001} face and small {101} face. As La2O3 was added and its content was increased, {223} and {110} faces were developed, and crystal habits of equidimensional forms changed into hexagonal prism form. In a charge of 8 mole% B2O3, Al2O3:La2O3=15:1, transparent corundum single crystals of equent form were grown. As the content of B2O3 was increased, twineed crystals which have twin law of 2-fold parallel to [0001], and composition plane of (110) were grown.

• Korean Journal of Crystallography
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• v.4 no.1
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• pp.11-17
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• 1993

Corundum single crystals were grown by the Czochralski technique. Relationships between crystal quality and crystal growth factors such as pulling rate, rotation rate and temperature of the melt were investigated. Optimum pulling and rotation rate for high quality corundum single crystal growth were 4.0mm/hr, 30rpm respectively. Pore was a main defect in corundum crystal and also discussed how to remove this defect by melt temperature control. Growth direction of as grown crystals was identified with(0001). And this direction had largest growth rate. Room temperature absorption spectra were measured and discussed for Cr3+ion doped and non-doped corundum crystals.

• Proceedings of the Korean Magnestics Society Conference
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• 2004.12a
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• pp.217-218
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• 2004

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.7 no.1
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• pp.47-58
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• 1997

In this study single crystalline corundum ($\alpha$-$Al_2O_3$) powders were prepared from gibbsite using hydrothermal growing processes. Addition of a mineralizer and the characteristics of solid substances were investigated to find their effects on the size distribution and crystalllnity of products. Experimental results showed that as the concentration of potassium hydroxide (KOH), a mineralizer, the particle size of corundum powders became larger at lower reaction temperatures. However, the size of corundum powders became smaller as the concentration of gibbsite increased in the feedstock. The hydrothermal synthetic conditions are also strongly dependent on the properties of hydrothermal solutions. Corundum powders which have the weight mean particle size of 1~10 $\mu\textrm{m}$ with shapes of hexagonal were prepared in this experiment.

• Korean Journal of Materials Research
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• v.32 no.2
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• pp.85-93
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• 2022

Porous mullite-corundum ceramics were prepared using organic foam impregnation method with alumina and silica as raw materials. The influence of alkaline treatment and surfactant modification on polyurethane foam were studied. Effects of sintering process and material composition on porous mullite-corundum ceramics were investigated. The results show that the hang-pulp quantity of polyurethane foam increases with alkaline treatment. After treatment with 3 wt% SDS solution, the hang-pulp quantity of polyurethane foam further improved. Open porosity of sample decreased with elevation of sintering temperature and holding time, and compressive strength of sample showed a trend opposite to the change of porosity. The open porosity of the sample was enhanced by the increase of m(Al₂O₃/SiO₂); the compressive strength decreased with increase of m(Al₂O₃/SiO₂). However, when m(Al₂O₃/SiO₂) was 2.5, the compressive strength of the sample reached 6.23 MPa, and the open porosity of the sample was 80.7 %.

• Journal of the Mineralogical Society of Korea
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• v.18 no.4 s.46
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• pp.313-323
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• 2005

XRD, XRF, EPMA, FT-IR, and SEM-CL studies were carried out in order to characterize gemological features of corundum from Tanzania. Fluorescence reaction of the Tanzanian corundum to short and long wave ultraviolet rays was weakly detected. Inclusions in Tanzanian corundum are divided into five types, Type I is fluid-rich inclusion, Type II is gas-rich inclusion, Type III is liquid $CO_{2}$ inclusion, Type IV is solid-rich inclusion, and Type V is a mixture of fluid and solid inclusion and daughter minerals. SEM-CL images show twin structure with growth texture, microphenocryst of spinel solid inclusions, massive and growth texture. Ruby and sapphire from Tanzania are distinctly distinguished by concentrations of Fe and Cr, and plotted in the particular field at $Al_{2}O_{3}/100-Cr_{2}O_{3}-Fe_{2}O_{3}$ diagram. According to FT-IR analysis, all corundum specimens from Tanzania showed the similar patterns, and absorption peaks of $455.09\~459.23\;cm^{-1},\;603.15\~611.71\;cm^{-1},\;1509.00\~1655.05\;cm^{-1}\;and\;3436.41\~3468.87\;cm^{-1}$. These distinctive characteristics mentioned above can be used to identify the locality and source of corundum stones from Tanzania.

• Bulletin of the Korean Chemical Society
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• v.20 no.10
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• pp.1205-1208
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• 1999

27Al NMR chemical shielding, quadrupolar coupling, and dipolar coupling interactions for corundum (α-Al2O3) are determined from the single-crystal 27 Al NMR spectra according to the rotation about three orthogonal axis. 27 Al NMR parameters obtained in this work with high accuracy are as follows: δiso = 7.4(4) ppm, QCC = 2.30(4) MHz, h = 0.08(3), and R = 2.0(3) kHz. This work appears to be the first NMR measurement of an aluminum-aluminum dipolar coupling interaction in α-Al2O3 crystals.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.6 no.2
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• pp.129-140
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• 1996

In this study, we have prepared corundum ($\alpha$-Al_{2}O_{3}$) single crystals from aluminum hydroxides by hydrothermal growing process and have investigated the reaction conditions. The hydrothermal conditions were mainly affected by reaction temperature, seed crystal and reaction time. Especially, seed crystal has strong effects on the particle size and crystallity of products. By adding seed crystal in Japanese gibbsite solution as the nutrient, hydrothermal reaction was performed for 2 hours at the reaction temperature of $460^{\circ}C$, to produce corundum powders which had weight mean particle diameter of $11\;\mu\textrm{m}$ with hexagonal crystal, Without adding seed crystal in Russian gibbstite solution, corundum powders that have weight mean particle diameter of $6\;\mu\textrm{m}$ with hexagonal crystals were also formed after 2 hours operation at the reaction temperature of $420^{\circ}C$.

• Journal of the Korea Furniture Society
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• v.21 no.2
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• pp.126-132
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• 2010

High wear resistances are obtained with an additional coating of the surface of the decor film in the same operation of impregnating with low viscosity melamine resin by liquid overlay system. The cellulosic fibers have a good adhesion to the corundum particles and keep them sufficiently homogeneous in the blend with the resin. The amount of these fibers in nearly as big as it is in a common overlay in relation to the resin. Therefore these fibers keep the resin inside during the press process and consequently very the surface of the decor print of the film. That means that the corundum particles are equally dissipated throughout the entire layer over the decor. The change of the color of the print is nearly not visible as the particles are almost equally dissipated. Looking to the flooring purposes of liquid overlay one can see that by the lesser exposure of the corundum particles on the very surface, there is no longer an abrasive surface but a feeling like a normal melamine surface.

• Economic and Environmental Geology
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• v.23 no.1
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• pp.11-23
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• 1990

Pyrophyllite, kaolinite, and alunite deposits distributing in Southwestern parts of Cheonnam are classified into three types of minerals assemblages by the results of X-ray diffraction analysis etc. The first mineral assemblages contains pyrophyllite, kaolinite, dickite, quartz, diaspore and/or corundum, the second one contains alunite inseads of corundum, and the third one contains alunite without pyrophyllite and diaspore. It is can be considered that the depoSits which consist mainly of pyrophyllite are formed higher temperature than the other deposits. Judging form the chemical analyses the chemical compositions of hydrothermal solutions acting to the deposits seem to be relatively simple. But the hydrothermal solutions which generated Dogcheon, Jugjcon, Ogmaesan, and Seongsan mine contain rather somewhat higher $K_2O$. The values of the Trace Elements and REE analysis of the host rocks of deposits suggest that the host rocks are these deposits are the last products of magmatic differentiation.