• Journal of the Korean Crystal Growth and Crystal Technology
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• v.24 no.3
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• pp.127-132
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• 2014

$Y_2O_3$-BN ceramic composites were fabricated from the slurries of yttria powder with average particle size of 3~10 ${\mu}m$. The slurry was fabricated by mixing PVA binder, NaOH for Ph control, PEG, BN powder and $Y_2O_3$ powder. The mixed $Y_2O_3$ powders were obtained by spray drying process from the slurry. The $Y_2O_3$-BN composite specimen was shaped in size of ${\O}14mm$ and then sintered at $1550^{\circ}C$ and $1600^{\circ}C$, respectively. The characteristics, microstructure, purities, densities, bulk resistance, thermal expansion, hardness and plasma resistance of the $Y_2O_3$-BN composites were investigated with the function of BN contents and sintering temperature.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.23 no.4
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• pp.173-179
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• 2013

Even though a rough diamond shape is irregular and rugged, it is easy to be processed to make gem, shaped facets (table, crown, pavilion and girdle) were precisely treated because they influence on the evaluation of diamond grading. Those specifications suitable for the standard round brilliant cut diamond polishing were investigated and in 95 % statistical confidence interval, standard deviation, mean and acceptable tolerance were examined. According to these variables (size, angle, depth, and thickness) distribution, the frequency analysis of ratings and proportions were compared with each other. The correlation between each variables and the evidence of influence represented in proportion were determined by the regression analysis applying LSM (Least Square Method). In this research, it was recognized that table sizes of the diamond jewels and pavilion depth (in %) influence the rating decision and in particular, the depth of pavilion acting as the main factor of proportions, also plays an important role in optical phenomena.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.18 no.2
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• pp.57-61
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• 2008

Non-nucleus Abalone half pearls were cultured by a new technique and their structural characteristics were analyzed using an electron microscopy. This technique was found to grow the pearls depending on the shape of the internal organ of an abalone because this technique induces the pearl layers without adding any nucleus on the specified damage region of a shell. The obtained pearls exhibit natural shapes with a specific luster. The SEM analysis shows that the pearl layers are about $0.34{\mu}m$ with an uniform thickness and the surface of the shell is characterized by the pyramid-shaped bulge with a regular arrangement, which is a typical feature of single-shell. These characteristics of the pearls are thought to develop in the highly-valued Korean gems.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.29 no.1
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• pp.6-11
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• 2019

Methylammonium lead halide ($MAPbX_3$, X = I, Br) thin films, used as the light absorber of perovskite solar cells, were prepared using the dual feed ultrasonic spray method. Going through a deposition at a substrate temperature of below $60^{\circ}C$ and then a final heat treatment at $75^{\circ}C$ for 5 minutes using dual feed ultrasonic spray method, $MAPbI_3$ single phase could be formed. Whereas undergoing a deposition at temperatures above $80^{\circ}C$, the spheroidal grains could be changed into rod-shaped fractal structures due to the decomposition of the perovskite phase. Furthermore, using the same method at a higher heat treatment temperature of $100^{\circ}C$, $MAPbI_{3-x}Br_x$ thin films could also be formed from $MAPbI_3$ and $MAPbIBr_2$ solution.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.30 no.6
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• pp.220-225
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• 2020

Gallium oxide nano-powder, the key starting material for IGZO target, is fabricated by gas phase synthesis using a new apparatus consist of reaction, transportation, and collection parts. As a result of gallium metal evaporation above 1150℃, Ga2O3 nano-powders, are successfully synthesized. The SEM images of the synthesized powders displace the spherical shaped powders without severe agglomeration. X-ray diffraction and PSA analysis show that the higher temperature at the reaction part results in the better crystallinity and larger powder size of the synthesized Ga2O3. To see the applicability to IGZO target, Ga2O3 nano-powders synthesized at 1250℃ are mixed with indium oxide and zinc oxide (In2O3 : Ga2O3 : ZnO = 1 : 1 : 1), and then sintered at 1400~1500℃. The highest sintered density of 5.83 g/㎤ (= 91 % of relative density) is achieved when sintered at 1450℃, showing better sinterability compared to the commercially available Ga2O3 powder, which has 5.61 g/㎤ of sintered density at the same condition.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.33 no.6
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• pp.268-275
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• 2023

This paper delves into the crucial realm of support structures in metal additive manufacturing (AM) processes and their direct impact on the stiffness of printed components. With the continuous evolution of AM technologies, optimizing support structures has become imperative to enhance the overall quality and performance of manufactured metal parts. Therefore, in this study, tensile specimens were manufactured using various representative support design variables such as support type, spacing, and penetration depth, and the differences in displacement-load curve were analyzed though tensile test. Using additively manufactured support shaped tensile specimen, the paper presents a comprehensive examination of the effect of support parameters on their stiffness. The findings contribute to advancing the understanding how to design supports to suppress thermal deformation of metal parts during AM process, thereby paving the way for enhanced design freedom and functional performance in the ever-expanding field of AM.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.28 no.3
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• pp.99-105
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• 2018

In order to avoid un-uniform crystallization on the surface of a quartz glass crucible that is known to affect the production yield of the single crystal silicon, Ba (barium) was selected as a crystallization promotor and the inner surface of the crucible was coated using Ba (barium hydroxide octahydrate)-solution by the spray pyrolysis method. For un-coated crucible, it was found that the crystallization of its surface started at $1350^{\circ}C$, and at $1450^{\circ}C$ the surface was uniformly crystallized with ${\beta}$-cristobalite phase. It was found that the crucible coated with Ba began to be crystallized from $1000^{\circ}C$ and was uniformly crystallized on the crucible surface at $1300^{\circ}C$. In this case, ${\alpha}$-cristobalite and needle-shaped $BaSi_2O_5$ phase were created and disappeared as a crystal phase, and the ${\beta}$-cristobalite phase was eventually evenly distributed over the Ba-coated crucible surface.

• Journal of the Korean Ceramic Society
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• v.39 no.4
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• pp.327-335
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• 2002

Experiments were conducted to investigate the synthesis characteristics of Precipitated Calcium Carbonate(for short PCC) in Ca(OH)$_2-CO_2-H_2O$ system by the continuous drop method of Ca(OH)$_2$ slurry into the solution containing $CO_2$(aq). When the flow rate of $CO_2$(g) increases and the concentration of Ca(OH)$_2$ slurry become low, the absorption rate of $CO_2$(g) become faster than the dissolution rate of Ca(OH)$_2$. Consequently, the growth of the calcite crystal plane is facilitated resulting in synthesis of $1.0{\mu}m$ of rhombohedral calcite. On the other hand, when the flow rate of $CO_2$(g) decreases and the concentration of Ca(OH)$_2-CO_2-H_2O$ slurry become high, new nuclei is created along with the crystal growth resulting in synthesis of $0.1{\mu}m$ of prismatic calcite. Maintaining 1.0wt% of Ca(OH)$_2-CO_2-H_2O$ slurry, 120 drops/min of drop rate and $25^{circ}C$ of temperature, the shape of PCC shows colloidal and spherical agglomerate at 100 mL/min of the flow rate of $CO_2$(g); the mixture of rhombohedral and plate-shaped calcite, at 200∼500 mL/min. Therefore, as the flow rate of $CO_2$(g) increases, the shape of PCC changes from colloidal and rhombohedral calcite to plate-shaped calcite. Maintaining 500 mL/min of the flow rate of $CO_2$(g), 120 drops/min of the drop rate of Ca(OH)$_2$ slurry, and $25^{circ}C$ of temperature, the shape of PCC shows the plate-shaped calcite at 1.0∼3.0 wt% of Ca(OH)$_2$ slurry; the hexagonal plate-shape calcite of the thickness of $0.1{\mu}m$ and the width of $1.0{\mu}m$, at 4.0 wt%.

• Journal of the Korean Electrochemical Society
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• v.5 no.3
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• pp.143-152
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• 2002

The growth of Polypyrrole film has been investigated during electropolymerization in an aqueous solution on bare and SAM modified gold electrodes by in-situ EQCM and ex-situ AFM. According to the result of cyclic voltammetry measurements, in the case of a bare gold electrode, the electrochemical deposition of polypyrrole were dependent on the limiting oxidative potential, but not on scan numbers. When the limiting potential higher than 0.8 V was applied on the electrode, the amount of polypyrrole deposited on a gold electrode was rapidly increased and the abnormal mass change attributed to the rearrangement of polypyrrole films was observed as the scan number increased. The polypyrrole film Prepared on electrodes modified with 1-dodecanethiol SAM or thiophene SAM grew 3-dimensionally with the rearrangement of film. However, in the case of BPUS SAM, 2-dimensional layer-by-layer growth of film was observed without the rearrangement of film. AFM images showed films with chain-shaped and/ or donut-shaped polymers when grown rapidly and a wrinkled film at the steady state condition.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.12 no.2
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• pp.68-72
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• 2002

The $\beta$-$FeSi_2$ and $\alpha$-$FeSi_2$ single crystals were synthesized by chemical vapour transport (CVT) using iodine as a transporting agent from the commercially available $FeSi_2$ powder. The $FeSi_2$ powder together with iodine were sealed in an evacuated quartz ampoule and the ampoule then being placed in two-zone electrical furnace for growing crystal. The CVT of $FeSi_2$ with iodine yielded $\beta$-$FeSi_2$ and $\alpha$-FeSi$_2$ single crystals at deposition temperature of 750 and $950^{\circ}C$ respectively. The source temperature was $1050^{\circ}C$ in both cases. The crystals of the $\alpha$-FeSi$_2$ phase were typically plate shaped with dimensions of about $10\times 10 \textrm{mm}^2$, whereas the crystals of orthorhombic $\beta$-$FeSi_2$ phase grew predominantly in the fonts of thin needle of about 10 mm in length. The composition of$\alpha$-FeSicrystal determined by electron probe microanalysis (EPMA) resulted in Si-rich $FeSi_{2.58}$ . 57. Furthermore, the CVT $\beta$-$FeSi_2$ crystal was found to be transformed to the high temperature $\alpha$-$FeSi_2$phase above $930^{\circ}C$.