• Journal of the Korean Crystal Growth and Crystal Technology
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• v.3 no.2
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• pp.117-124
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• 1993

It was found that the basic principle of continuous crystal growth method was following as; the powder supplied from the feeding system is molten in the graphite crucible under the ambient gas. After forming the molten zone in the lower part of the crucible, the seed crystal is deeped into the melt and pulled down with the rotation so that the melt crystallized from the seed. When the lowering rate, rotation rate, feeding rate and temperature are correct, the single crystal can grow. The critical melt level, the feeding rate, the growth rate, the change of the shape of molten zone by the graphite susceptor and crucible, the position of work coil, the balance between the gravitational force of melt and the centrifugal force originated from the rotation of seed which are the variables of the crystal growth and the sintering phenomenon of melt surface were researched.

• Bulletin of the Korean Chemical Society
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• v.32 no.2
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• pp.725-727
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• 2011

• 제어로봇시스템학회:학술대회논문집
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• 2003.10a
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• pp.1196-1200
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• 2003

The degree of supersaturation is an important measure for the operation of crystallization processes, because it is directly related to the control of crystal size distribution and shape. A conventional technique utilizing solution composition and temperature has a variety of problems caused from the measurement error and the handling of analyzing samples. A monitoring system of the supersaturation using a quartz crystal sensor is proposed here, and its performance is examined applying different manipulations of coolant temperature. The experimental outcome and photographic examination indicate that the measurements of resonant frequency and resistance of the sensor can be used for the prediction of the formation and growth of solid crystal from the crystallization process. The monitoring system eliminates the intrinsic error source of the conventional system to give the improved measurement and on-line application availability.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.12
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• pp.1667-1675
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• 2001

Numerical simulations are carried out for the liquid encapsulant Czochralski(LEC) by imposing a magnetic field. The use of a magnetic field to the crystal growth is to suppress melt convection and to improve the homogeneity of the crystal. In the present numerical investigation, we focus on the range of 0-0.3Tesla strength for the axial and cusped magnetic field and the effect of the magnetic field on the melt-crystal interface, flow field and temperature distribution which are the major factors to determine the quality of the single crystal are of particular interest. For both axial and cusped magnetic field, increase of the magnetic field strength causes a more convex interface to the crystal. In general, the flow is weakened by the application of magnetic field so that the shape of the melt-crystal interface and the transport phenomena are affected by the change of the flow and temperature field.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.5 no.1
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• pp.44-49
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• 1995

Abstract The surface of 6H - SiC bulk crystal grown by sublimation process was investigated by optical microscope observation. Since, in the 6H crystal growing, the crystal had the habitual step growth attitude such that the lateral growth rate along the random a - axis orientation was higher than that along the c - axis of the growth direction, then many steps were developed. There were, also, many micropipes on the surface in the form of as-like large voids. However, they were differenciated with pores and cross- sectional shape of them were close to the circle. In this study, many micropipes, planar defects and the growth steps appeared on the grown crystal surface were investigated.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.1 no.1
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• pp.59-70
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• 1991

ZnO fine powder was prepared by the batch precipitation process using $ZnCl_2$ and hexamethylenetetramine solution as a mother solution. When the concentrations of $ZnCl_2$solution were $0.1mol/\ell$ and 0.05mol/-, the particles of rod shape were obtained when the conentration of $ZnCl_2$solution was $0.01mol/\ell$, the particle of plate shape was obtained. When the hexamethylenetetramine as a precipitants was used, pH was raised slow during a few minute be-cause of slow hydrolysis rate of hexamethylenetetramine. For rapid raising of pH during initial reac-tion time, $NH_4$OH was added as nucleant. When $NH_4$OH as a nucleant was added, obtained particle was shape of granular and the mean particle size was $0.41\mu\textrm{m}$. After calcination at $500^{\circ}C$ during 1hour, all of remained organic phase was removed but the shape of particles was not changed. But pa-rticles were slightly shrunk in comparision with before calcined particles.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.12 no.4
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• pp.172-177
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• 2002

The CuZnAl alloys have some advantages against other shape memory alloys, such as the widely variable transformation temperature, the low cost and easy fabrication. The alloys have been produced mostly by metallurgical methods. Thereby a tendency to large grain sizes is observed, which causes brittle properties of the materials. In order to avoid these deficiencies a special powder metallurgical process, SPS(spark plasma sintering), is applied in the present investigation. The starting materials were the pure (99.9 %) Cu, Zn and Al element powders with different particle size. The relatively fine grained and homogeneous Cu-24.78Zn-9.11Al (at.%) and Cu-13.22Zn-17.24Al (at.%) shape memory alloys were obtained using the powders with size of 75-150 $\mu$m. The average grain size is about 70 $\mu$m and the phases at room temperature are the austenitic and martensitic phase respectively.

• Journal of the Korean Ceramic Society
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• v.25 no.1
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• pp.78-82
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• 1988

Good quality LiNbO3 single crystals which can be applied to SAW devices, were grown by Czochralski method. It was observed that the gas-bubbles were concentrated in ring shape at the outer part of grown crystals, and this anomaly was illustrated by modeling the mechanism of gas-bubble entrapment according to the melt flow pattern in the crucible. And this mechanism was also encertained by observation of solid-liquid interface shape of grown crystals. The optimal condition for good quality crystals was known that the solid-liquid interface shape was slightly concave.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.8 no.3
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• pp.383-387
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• 1998

The vacuum-Bridgman equipment for large size diameter (4 inch more over) crystal growth was organized simply and the $CaF_2$ single crystal which was grown in the conditions of growth rate of 2mm/hr, freezing temperature gradient of $12^{\circ}C$/cm, have analyzed to keep excellent properties. Using Mo thermal reflector of umbrella shape, it could be eliminated the formation of polycrystalline. The preferential growth direction was (111) and the calculated lattice parameter was $5.460 \AA$ by XRD peaks. The secondary phases, also, was not formed by means of powder-XRD analysis. The value of EPD is $1.4{\times}10^4 \textrm{cm}^{-2}$ and the optical quality, which is the transmittance is 91% up in UV region, is suitable for optical components of UV applications.

• Journal of Environmental Science International
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• v.17 no.9
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• pp.981-992
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• 2008

This study examined how to produce new methods of copper (II) sulfate crystallization by using a small-scale chemistry tool such as small-scale reaction surface and petri dish. The making of copper(II) sulfate is included in the 5th grade elementary science textbooks. Various copper(II) compounds were reacted with a 2 M sulfuric acid solution. The result of this study is as follows: Seven small amounts of copper(II) compounds were reacted with a few drops of 2 M sulfuric acid solution at room temperature to make a copper(II) sulfate crystal of triclinic shape. Using the petri dish method, a copper(II) sulfate crystal could be identified within one hour of reacting copper(II) hydroxide, copper(II) carbonate, copper(II) nitrate, copper(II) perchlorate, cupric(II) formate from a few drops of 2 M sulfuric acid solution at room temperature. When using the lap top method for copper(II) perchlorate, cupric formate, a proper crystal could be identified within one hour as well. SSC methods were used for the first time to make a copper sulfate crystal via chemical reaction. We can make a copper(II) sulfate crystal using a simple method which is easier, safer and saves time in class. And since a small quantity of chemicals are being used in SSC chemical methods, waste is greatly reduced. This lessens the amount of environmental problems caused by the experiment. This can be helpful in preserving nature. In addition the cost of chemical and laboratory equipment is greatly reduced because it uses material that we find in our daily lives. There will be continued study of small-scale methods such as improvement of new programs, study and training of teachers, and securing SSC tools. I would like to suggest such as SSC methods are applicable in elementary School Science. I would like it to become a wide spread program.