• Journal of the Korean Crystal Growth and Crystal Technology
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• v.33 no.1
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• pp.22-30
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• 2023

Currently, almost all product development in the jewelry industry utilizes 3D CAD and 3D printing. In this situation, 3D CAD modeling and 3D printing ability units in colleges, Tomorrow Learning Card Education, and Course Evaluation-type jewelry design related education are conducted with developed curriculum based on the standards for training standards, training hours, training equipment, and practice materials presented by NCS. Accordingly, this study analyzes 3D CAD modeling and 3D printing training facilities, training hours, training equipment, etc into three categories of NCS precious metal processing and jewelry design, and studies the development of educational systems such as 3D CAD/3D printing curriculum and various environments that meet these standards. Education using this 3D CAD/3D printing education system will enable us to continuously supply professional talent with practical skills not only in the jewelry industry but also in the entire 3D CAD/3D printing manufacturing industry, which is called as one of the pillars of the 4th Industry. The quality of employment of trainees receiving education and the long-term retention rate after employed can also have a positive effect. In addition, excellent educational performance will help improve the recruitment rate of new students in jewelry jobs or manufacturing-related departments, which are difficult to recruit new students in recent years.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.33 no.3
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• pp.97-103
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• 2023

Barrier films for transparent packaging materials with excellent moisture barrier properties are prepared, utilizing a nanoclay dispersion coating layer formed after a pretreatment process of plasma activation surface treatment process under vacuum at room temperature. Attention is paid on optimizing the coupling additive through the appropriate crosslinking process and optimal dispersion process of the coating process to enhance adhesion. Analysis of the functional coating thin film shows that the water vapor transmission rate is less than 10 g/m²/24 hrs (ASTM F-1249) and the oxygen transmission rate is less than 30 cc/m²/24 hrs (ASTM D3985). It is shown that water barrier properties of coating thin film prepared in this study are greater than conventional untreated films by 10 times or more. The thickness of the transparent gas barrier film is within 0.1 mm, and the transparent gas barrier complex is implemented in two layers. In the study of PET thin film interface characteristics, FT-IR experimental analysis shows the reaction activity was optimized at RDS 1.125 %.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.34 no.4
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• pp.131-138
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• 2024

In this study, the microstructure and plasma resistance characteristics of 35Bi₂O₃-15Al₂O₃-50SiO₂ (BiAl SiO) and 35Bi₂O₃-7.5Al₂O₃-50SiO₂-7.5AlF₃ (BiAlSiOF) glass layers coated on sintered alumina substrates were investigated according to the sintering conditions. The coated layers were formed using the bar coating method and then sintered at a temperature in the range of 700~900℃, which corresponds to the temperature before and after the hemisphere forming temperature, after a debinding process. The plasma resistance of the two coated glasses was approximately 2~3 times higher than that of the quartz glass, and in particular, the BiAlSiOF glass film with F added showed higher plasma resistance than BiAlSiO. It is thought to be due to the effect of suppressing the reaction with fluorine gas by adding fluorine to the glass. When the sintering time was increased at 700℃ and 800℃, the plasma resistance of both glasses improved, but when the sintering temperature was increased to 900℃, the plasma resistance decreased again (i.e., the etching rate increased). This phenomenon is thought to be related to the crystallization behavior of both glasses. The change in plasma resistance depending on the sintering conditions is thought to be related to the appearance of Al and Bi-rich phases.

• Journal of the Korean Ceramic Society
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• v.37 no.1
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• pp.50-56
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• 2000

Precursor gels with the composition of xZrO2·(100-x)SiO2 systems (x=10, 20 and 30 mol%) were prepared by the sol-gel method. Kinetic parameters, such as activation energy, Avrami's exponent, n, and dimensionality crystal growth value, m, have been simultaneously calculated from the DTA data using Kissinger and Matusita equations. The crystallite size dependence of tetragonal to monoclinic transformation of ZrO2 was investigated using XRD, in relation to the fracture toughness. The crystallization of tetragonal ZrO2 occurred through 3-dimensional diffusiion controlled growth(n=m=2) and the activation energy for crystallization was calculated using Kissinger and Matusita equations, as about 310∼325±10kJ/mol. The growth of t-ZrO2, in proportion to the cube of radius, increased with increasing heating temperature and hteat-treatment time. It was suggested that the diffusion of Zr4+ ions by Ostwald ripening was rate-limiting process for thegrowth of t-ZrO2 crystallite size. The fracture toughness of xZrO2·(100-x)SiO2 systems glass ceramics increased with increasing crystallite size of t-ZrO2. The fracture toughness of 30ZrO2·70SiO2 system glass ceramics heated at 1,100℃ for 5h was 4.84 MPam1/2 at a critical crystaliite size of 40 nm.

• Korean Journal of Materials Research
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• v.15 no.11
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• pp.741-744
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• 2005

Atomic layer deposition (ALD) is a very promising deposition technique for ZnO thin films. However, there have been very few reports on ZnO grown by ALD. Effects of substrate temperature in both ALD and post annealing on the microstructure and PL properties of ZnO thin films were investigated using X-ray diffraction, photoluminescence, and scanning electron microscopy. The temperature window of ALD is found to be between $130-180^{\circ}C$. The growth rate of ZnO thin film increases as the substrate temperature increases in the temperature range except the temperature window. The crystal quality depends most strongly on the substrate temperature among all the growth parameters of ALD. The crystallinity of the film is improved by increasing the growth thine per ALD cycle or doing post-annealing treatment. The grain size of the film tends to increase and the grain shape tends to change from a worm-like longish shape to a round one as the annealing temperature increases from $600^{\circ}C\;to\;1,000^{\circ}C$.

• Journal of the Korean Ceramic Society
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• v.48 no.4
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• pp.263-268
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• 2011

ZnO hexagonal rods grown in aqueous solution can be changed into a tubular shape by two-step aging in the course of the growing process. In the first step, hexagonal ZnO rods is grown by aging at $90^{\circ}C$ under a highly supersaturated aqueous solution giving rise to a fast precipitation rate. Meanwhile, during the second step aging at $60^{\circ}C$ in the same aqueous solution, the hexagonal polar face (001) having higher surface energy than (010) side planes dissolves to minimize surface energy. Hence the flat (001) face changes to a craterlike face and the hexagonal rod length of ZnO decreases at an initial-stage of this step aging. The formation of the (101) wedge-type faces is ascribed to the resultant of competitive reactions between the dissolution of polar face minimizing the surface energy which is a dominant reaction at the initial stage and the precipitation reaction dissipating supersaturation. At a later stage of the second-step the reaction rates of these two processes in the aqueous solution become similar and the overall reaction is terminated.

• Macromolecular Research
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• v.15 no.7
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• pp.662-670
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• 2007

The crystallization behavior and fine structure of poly(ethylene terephthalate) (PET)/A-zeolite nanocomposites were assessed via differential scanning calorimetry (DSC) and time-resolved small-angle X-ray scattering (TR-SAXS). The Avrami exponent increased from 3.5 to approximately 4.5 with increasing A-zeolite contents, thereby indicating a change in crystal growth formation. The rate constant, k, evidenced an increasing trend with increases in A-zeolite contents. The SAXS data revealed morphological changes occurring during isothermal crystallization. As the zeolite content increased, the long period and amorphous region size also increased. It has been suggested that, since PET molecules passed through the zeolite pores, some of them are rejected into the amorphous region, thereby resulting in increased amorphous region size and increased long period, respectively. In addition, as PET chains piercing into A-zeolite pores cannot precipitate perfect crystal folding, imperfect crystals begin to melt at an earlier temperature, as was revealed by the SAXS profiles obtained during heating. However, the spherulite size was reduced with increasing nanofiller content, because impingement between adjacent spherulites in the nanocomposite occurs earlier than that of homo PET, due to the increase in nucleating sites.

• Journal of the Semiconductor & Display Technology
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• v.9 no.4
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• pp.7-12
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• 2010

Field-emission characteristics of carbon nanotubes(CNTs), which were grown on conical-type tungsten micro-tips by using an electrophoretic deposition(EPD) method, were examined. The EPD method proved to be convenient to manipulate and arrange CNTs from well dispersed suspensions onto such tip-type substrates. The growth rate of CNTs was proportional to the applied d.c. bias voltage and the process time. It was observed from the Raman study that the EPDproduced CNTs showed better crystal qualities with the Raman intensity ratio( $I_D$/$I_G$) of 0.41-0.42 than the CVD-produced CNTs and their crystal qualities could be further improved by thermal annealing. The electron emitters based on the EPDCNTs showed excellent field emission properties, such as the threshold voltage for electron emission of about 620 V and the maximum emission current of about 345 ${\mu}A$. In addition, the EPD-CNTs exhibited the stable long-term(up to 40 h) emission capability and the emission stability was enhanced by thermal annealing.

• Bulletin of the Korean Chemical Society
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• v.5 no.2
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• pp.73-78
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• 1984

Superplastic alloys generally exhibit a three-stage sigmoidal variation of stress (f) with strain rate (s), the stages being named region 1, 2 and 3 according to the increasing order of stress or strain rate. In the recent years, two different types of papers have been published on the plastic deformation of Zn-22% Al eutectoid in region Ⅰ differing in strain-rate sensitivity m (= dln f/dln s). In this paper, the data of the two groups have been analysed by applying Kim and Ree's theory of superplastic deformation. (1) We obtained the parametric values of $X_{gj}/{\alpha}_{gj}\;and\;{\beta)_{gj}$ (g: grain boundary, j = 1,2 indicating flow units) appearing in Kim and Ree's theory [Eq. (2a)]. (2) It was found that the value of $X_{g^2}/{\alpha}_{g^2}$ is small for the group data with small m, i.e., ${\alpha}_{g^2}$, which is proportional to the size of flow unit g2, is large whereas ${\alpha}_{g^2}$ is small for the groups data with large m, i.e., the size of the flow unit g2 is small. In other words, the two types of behavior occur by the size difference in the flow units. (3) From the ${\beta}_{gj}$ value, which is proportional to the relaxation time of flow unit gj, the ${\Delta}H_{gj}^{\neq}$ for the flow process was calculated, and found that ${\Delta}H_{g^2}^{\neq}$ is large for the group data with small m whereas it is small for the group data with large m. (4) The flow-unit growth was studied, but it was concluded that this effect is not so important for differentiating the two groups. (5) The difference in ${\alpha}_{g^2}$ and in the growth rate of flow units is caused by minute impurities, crystal faults, etc., introduced in the sample preparation.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.18 no.6
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• pp.237-241
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• 2008

Hot-press sintering of AlN ceramics were carried out with $Y_2O_3$ as sintering additive at a sintering temperature $1,750{\sim}1,850^{\circ}C$. The effect of $Y_2O_3$ addition and sintering time on sintering behavior and thermal conductivity of AlN ceramics was investigated. $Y_2O_3$ added AlN showed noticeably higher denazification rate than pure AlN. The thermal conductivity of AlN specimens was promoted by the addition of $Y_2O_3$ in spite of the formation of YAG secondary phase in AlN grain boundaries and grain boundary triple junction because $Y_2O_3$ addition could reduced the oxygen contents in AlN lattice which is primary factor of thermal conductivity. Typically, the thermal conductivity of 5 wt% $Y_2O_3$ added specimen was dramatically improved by the increase of sintering time because the elimination of YAG secondary phases from the grain boundary due to the evaporation, as well as the grain-growth of AlN grains.