• Proceedings of the Korea Association of Crystal Growth Conference
• /
• 1996.06b
• /
• pp.285-309
• /
• 1996

Non oxide ceramics such as nitrides of transition metals have shown significant potential for future economic impact, in diverse applications in ceramic, aerospace and electronic industries, as refractory products, abrasives and cutting tools, aircraft components, and semi-conductor substrates amid others. Combustion synthesis has become an attractive alternative to the conventional furnace technology to produce these materials cheaply, faster and at a higher level of purity. However he process os highly exothermic and manifests complex dynamics due to its strongly non-linear nature. In order to develop an understanding of this process and to study the effect of operational parameters on the final outcome, numerical modeling is necessary, which would generated essential knowledge to help scale-up the process. the model is based on a system of parabolic-hyperbolic partial differential equations representing the heat, mass and momentum conservation relations. The model also takes into account structural change due to sintering and volumetric expansion, and their effect on the transport properties of the system. The solutions of these equations exhibit steep moving spatial gradients in the form of reaction fronts, propagating in space with variable velocity, which gives rise to varying time scales. To cope with the possibility of extremely abrupt changes in the values of the solution over very short distances, adaptive mesh techniques can be applied to resolve the high activity regions by ordering grid points in appropriate places. To avoid a control volume formulation of the solution of partial differential equations, a simple orthogonal, adaptive-mesh technique is employed. This involves separate adaptation in the x and y directions. Through simple analysis and numerical examples, the adaptive mesh is shown to give significant increase in accuracy in the computations.

• Bulletin of the Korean Chemical Society
• /
• v.34 no.2
• /
• pp.622-628
• /
• 2013

Nanocrystalline spinel lithium manganese oxide ($LiMn_2O_4$) powders with narrow-size-distribution, pure-phase particles, and high crystallinity with an average crystallite size of about 70 nm were synthesized at $600^{\circ}C$ for 6 h in air by freeze drying method. Spinel $LiMn_2O_4$ is also prepared by sol-gel using citric acid as a chelating agent. The influence of different parameters such as pH conditions, solvent, molar ratio of citric acid to total metal ions, calcination temperature, starting material on the structure, morphology and purity of this oxide was investigated. The results of sol-gel method show that pure $LiMn_2O_4$ with average crystallite size of about 130 nm can be produced from nitrate salts as starting materials at $800^{\circ}C$ for 6 h in air. The optimum pH and molar ratio of chelating agent to total metal ions are $4{\leq}pH{\leq}6$ and 1.0, respectively. A possible mechanism on the formation of the nanocrystallines synthesized by sol-gel was also discussed. At the end a comparison of the differences between two methods was made on the basis of x-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and thermogravimetric analysis (TGA) tests.

• Journal of Fashion Business
• /
• v.19 no.5
• /
• pp.128-138
• /
• 2015

The purpose of this study is to explore the characteristics and recent trends of Korean herbal medicine cosmetics brand logos and to shed light on the identities of herbal medicine cosmetics in Korea. Ultimately this study aims to seek ways to develop strategic global brands distinguished from other brands, and providing the basic data for such development. In order to investigate the characteristics of brand logos, the researcher of this study chose 11 Korean Herbal Medicine Cosmetics Brands marketed today and collected information related to the brands from their websites. The visual characteristics of the logos currently used by Korean herbal medicine cosmetics can be summarized as follows. Most brand logos include marks consisting of Chinese letters written in calligraphy styles to represent the brand information of'Korean herbal medicine.' As for colors, most brands use mostly black and gold to present luxurious images, or convey strong impressions through stark contrast between black, red and white, hoping to distinguish themselves from other cosmetic products. An analysis of the linguistic characteristics of herbal medicine cosmetics in South Korea revealed that most brands use associative and freestanding brand names which suggest that the user's appearance will improve by using the products they represent. Using such names that convey oriental purity and mysterious meanings, trying to capture the deepest beauty with the best quality, the brands construct brand images that are luxurious and high-class. Most of the brands currently used by Korean herbal medicine cosmetics employ components that emphasize the functional aspect of Korean herbal medicine cosmetics. To secure the status of world-class brands, however, it is imperative to conduct research on brand logos capable of establishing identities distinguished from others.

• Korean Journal of Materials Research
• /
• v.25 no.8
• /
• pp.386-390
• /
• 2015

Fe-base superalloy powders with $Y_2O_3$ dispersion were prepared by high energy ball milling, followed by spark plasma sintering for consolidation. High-purity elemental powders with different Fe powder sizes of 24 and 50 mm were used for the preparation of $Fe-20Cr-4.5Al-0.5Ti-O.5Y_2O_3$ powder mixtures (wt%). The milling process of the powders was carried out in a horizontal rotary ball mill using a stainless steel vial and balls. The milling times of 1 to 5 h by constant operation (350 rpm, ball-to-powder ratio of 30:1 in weight) or cycle operation (1300 rpm for 4 min and 900 rpm for 1 min, 15:1) were applied. Microstructural observation revealed that the crystalline size of Fe decreased with an increase in milling time by cyclic operation and was about 15 nm after 3 h, forming a FeCr alloy phase. The cyclic operation had an advantage over constant milling in that a smaller-agglomerated structure was obtained. The milled powders were sintered at $1100^{\circ}C$ for 30 min in vacuum. With an increase in milling time, the sintered specimen showed a more homogeneous microstructure. In addition, a homogenous distribution of Y-compound particles in the grain boundary was confirmed by EDX analysis.

• Journal of the Korean Ceramic Society
• /
• v.51 no.6
• /
• pp.544-548
• /
• 2014

Aluminum nitride was synthesized using a carbothermal method from mesoporous alumina having a high surface area (> $1,000m^2/g$) as an aluminum source and CNTs (carbon nano tubes) as a carbon source. In this case the mesoporous alumina was used as the starting material instead of ${\alpha}-Al_2O_3$ with the expectation that the mesopores in mesoporous alumina act as channels for N2 gas and elimination of CO generated as by-product. It is also expected that the synthetic temperature should be lower compared to the use of ${\alpha}-Al_2O_3$ as a starting material due to its high surface area. The crystallinity of the produced aluminum nitride was studied by XRD and FT-IR, and the microstructure was investigated by FE-SEM. Also the purity of the aluminum nitride was analyzed through N/O determinator and ICP analysis.

• KSBB Journal
• /
• v.10 no.3
• /
• pp.271-282
• /
• 1995

The authentic hGH converted from met-hGH by immobilized ApM was purified by successive chromatographic processes based on the differences in isoelectric points, hydrophobicities and charges. The final recovery yield was about 14.1% and the specific activity of the purified hGH was 2.75IU per mg when assayed by enzyme immunoassay. The purified hGH was verified to be authentic hGH through the analysis of amino acid composition, amino-terminal amino acid sequence, carboxy-terminal amino acid and tryptic peptide map. The purity of purified hGH was higher than that of commercial hGH when assessed by SDS-PAGE, PAGE, IEF and HSGF. In weight-gain assay and tibia test with hypophysectomized rats, the hGH produced in this study showed the same growth effect as the commercial hGH.

• Analytical Science and Technology
• /
• v.29 no.4
• /
• pp.194-201
• /
• 2016

The stability comparison tests on purified bee venom (PBV) and bee venom melittin (BVM) in different conditions of temperature, solvent, and concentration were studied. High purity BVM (98.2 %) was separated from PBV by prep-HPLC (column, C₄) and used to stability tests in aqueous phase. The stability of the PBV has been increased in the saline solution, while BVM was reduced. In distilled water, the stability of PBV has been reduced, while BVM showed an increasing result. As a result, the appropriate conditions for maintaining the long term stability of BVM were found to be the low temperature (4 ℃), distilled water, and concentration (1.0 mg/mL).

• Resources Recycling
• /
• v.26 no.1
• /
• pp.16-21
• /
• 2017

This paper relates to the synthesis of a source powder for SiC crystal growth. ${\beta}-SiC$ powders are synthesized at high temperatures (>$1400^{\circ}C$) by a reaction between silicon powder and carbon powder. The reaction is carried out in a graphite crucible operating in a vacuum ambient (or Ar gas) over a period of time sufficient to cause the Si+C mixture to react and form poly-crystalline SiC powder. End-product characterizations are pursued with X-ray diffraction analysis, SEM/EDS, particle size analyzer and ICP-OES. The purity of the end-product was analyzed with the Korean Standard KS L 1612.

• The Transactions of The Korean Institute of Electrical Engineers
• /
• v.67 no.6
• /
• pp.789-793
• /
• 2018

All transparent metal oxide photoelectric device based on $V_2O_5$ was fabricated with structure of $V_2O_5/ZnO/ITO$ by magnetron sputtering system. $V_2O_5$ was deposited by reactive sputtering system with 4 inch vanadium target (purity 99.99%). In order to achieve p-n junction, p-type $V_2O_5$ was deposited onto the n-type ZnO layer. The ITO (indium tin oxide) was applied as the electron transporting layer for effective collection of the photo-induced electrons. Electrical and optical properties were analyzed. The Mott-Schottky analysis was applied to investigate the energy band diagram through the metal oxide layers. The $V_2O_5/ZnO/ITO$ photoelectric device has a rectifying ratio of 99.25 and photoresponse ratios of 1.6, 4.88 and 2.68 under different wavelength light illumination of 455 nm, 560 nm and 740 nm. Superior optical properties were realized with the high transmittance of average 70 % for visible light range. Transparent $V_2O_5$ layer absorbs the short wavelength light efficiently while passing the visible light. This research may provide a route for all-transparent photoelectric devices based on the adoption of the emerging p-type $V_2O_5$ metal oxide layer.

• Resources Recycling
• /
• v.3 no.1
• /
• pp.9-16
• /
• 1994

Fine cobalt metal powders was produced from domestic Stellite scrap by decomposing it with molten sodium hydroxide. Complete decomposition of the scrap could be obtained with the weigth ratio of sodium hydroxide to Stellite being about 2 at the temperature ranges of $750~800^{\circ}C$ for an hour. The cobalt-bearing compound was identified as $Co_2O_3{\dot}H_2O$ by X-ray analysis and D.T.-T.G.a.. The compound was then digested in HCI to form cobalt chloride, and after iron removal by adjusting the pH of the solution, cobaltous or cobaltic hydroxide was precipitated at the pH of about 13 or 4, respectively. The precipitates were reduced by hydrogen in the temperatures of $400~500^{\circ}C$ to fine cobalt powders of high purity with the size of 1.0 to $1.5\mu\textrm{m}$. The recovery of cobalt from Stellite scrap was about 75~86% by weight.