• Journal of Microbiology and Biotechnology
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• 제28권4호
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• pp.534-541
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• 2018

Kimchi (a traditional Korean fermented vegetable) was prepared with a starter, Lactobacillus zymae GU240 producing ${\gamma}$-aminobutyric acid (GABA), and one precursor of GABA (glutamic acid, glutamic acid monosodium salt (MSG), or kelp extract). L. zymae GU240, an isolate from kimchi, can grow at 7% NaCl and low temperature. Five different kimchi samples were fermented for 20 weeks at $-1^{\circ}C$. Kimchi with starter alone could not produce GABA. The GABA content was highest in kimchi with co-inoculation of the starter and MSG (1% (w/w)). Kimchi co-inoculated with the starter and kelp extract powder (3% (w/w)) had the second highest GABA content. Addition of glutamic acid powder (1% (w/w)) caused a reduction in the pH level of kimchi and growth inhibition of lactic acid bacteria and yeasts. Kimchi samples with MSG or kelp extract showed improvement of sensory evaluation scores. The results demonstrate the possibility to produce kimchi with improved functionality and taste by using L. zymae GU240 as a starter along with a suitable precursor such as MSG or kelp extract.

• 한국분말재료학회지
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• 제25권1호
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• pp.54-59
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• 2018

Sb-doped $SnO_2$ (ATO) transparent conducting films are fabricated using horizontal ultrasonic spray pyrolysis deposition (HUSPD) to form uniform and compact film structures with homogeneously supplied precursor solution. To optimize the molar concentration and transparent conducting performance of the ATO films using HUSPD, we use precursor solutions of 0.15, 0.20, 0.25, and 0.30 M. As the molar concentration increases, the resultant ATO films exhibit more compact surface structures because of the larger crystallite sizes and higher ATO crystallinity because of the greater thickness from the accelerated growth of ATO. Thus, the ATO films prepared at 0.25 M have the best transparent conducting performance ($12.60{\pm}0.21{\Omega}/{\square}$ sheet resistance and 80.83% optical transmittance) and the highest figure-of-merit value ($9.44{\pm}0.17{\times}10^{-3}{\Omega}^{-1}$). The improvement in transparent conducting performance is attributed to the enhanced carrier concentration by the improved ATO crystallinity and Hall mobility with the compact surface structure and preferred (211) orientation, ascribed to the accelerated growth of ATO at the optimized molar concentration. Therefore, ATO films fabricated using HUSPD are transparent conducting film candidates for optoelectronic devices.

• 한국분말재료학회지
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• 제15권2호
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• pp.125-135
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• 2008

[ $TiO_2$ ] nanotubes for photocatalytic application have been synthesized by hydrothermal method. $TiO_2$ nanotubes are formed by washing process after reaction in alkalic solution. Nanotubes with different morphology have been fabricated by changing NaOH concentration, temperature and time. $TiO_2$ nanoparticles were treated inside NaOH aqueous solution in a Teflon vessel at $110^{\circ}C$ for 20 h, after which they were washed with HCl aqueous solution and deionized water. Nanotube with the most perfect morphology was formed from 0.1 N HCl washing treatment. $TiO_2$ nanotube was also obtained when the precursor was washed with other washing solutions such as $NH_4OH$, NaCl, $K_2SO_4$, and $Na_2SO_3$. Therefore, it was suggested that $Na^+$ ion combined inside the precursor compound slowly comes out from the structure, leaving nanosheet morphology of $TiO_2$ compounds, which in turn become the nanotube in the presence of hydroxyl ion. To stabilize the sheet morphology, the different type of washing treatment solution might be considered such as amine class compounds.

• 한국분말재료학회지
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• 제29권3호
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• pp.207-212
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• 2022

Nanosized rutile titanium dioxide (TiO₂) is used in inorganic pigments and cosmetics because of its high whiteness and duality. The high quality of the white pigments depends on their surface coating technique via the solgel process. SiO₂ coatings are required to improve the dispersibility, UV-blocking, and whiteness of TiO₂. Tetraethyl orthosilicate (TEOS) is an important coating precursor owing to its ability to control various thicknesses and densities. In addition, we use Na₂SiO₃ (sodium silicate) as a precursor because of its low cost. Compared to TEOS, which controls the pH using a basic catalyst, Na₂SiO₃ controls the pH using an acid catalyst, giving a uniform coating. The coating thickness of TiO₂ is controlled using a surface modifier, cetrimonium bromide, which is used in various applications. The shape and thickness of the nanosized coating layer on TiO₂ are analyzed using transmission electron microscopy, and the SiO₂ nanoparticle behavior in terms of the before-and-after size distribution is measured using a particle size analyzer. The color measurements of the SiO₂ pigment are performed using UV-visible spectroscopy.

• 한국결정성장학회지
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• 제6권2호
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• pp.121-128
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• 1996

Floating zone법으로 $LiNbO_3$ 단결정올 육성하는데 있어서 원료분말 합성과 원료봉 소결 과정의 최척의 조건을 설험적으로 조사하였다. 원료분말 합성사 낮은 고상반응 온도(700, $800^{\circ}C$)에서는 미량의 $Li_2CO_3$와 $Nb_2O_5$가 미반응상태로 남아있고, 고상반응 온도가 높을 때 ($1000^{\circ}C$)에는 입자성장이 일어나 후속공정인 원료봉 소결에 악영향을 미침이 확인되었다. $950^{\circ}C$에서 12시간 고상반응시킨 원료분말이 $LiNbO_3$의 결정상을 가지면서 미세한 결정립 크기와 균일한 크기분포를 보여 $950^{\circ}C$, 12시간이 최적의 원료분말 합성조건이었다. 원료봉 소결시 소 결온도가 높아질수록, 또 소결시간이 늘어날수록 치밀도가 증가하고 업자성장 양상이 급격히 증가함을 알 수 었었다. $1100^{\circ}C$에서 2시간 동안 소결한 원료봉이 치밀하고, 작은 결정립 크기 와 균얼한 크기분포를 나타내어 floating zone법에 의한 $LiNbO_3$ 단결정성장에 가장 적합한 최적 의 소결 조건은 $1100^{\circ}C$, 2시간엄이 확인되었다.

• 한국분말재료학회지
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• 제17권4호
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• pp.263-269
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• 2010

Hexagonal barium ferrite ($BaFe_{12}O_{19}$) nano-particles have been successfully fabricated by spraypylorysis process. $BaFe_{12}O_{19}$ precursor solutions were synthesized by self-assembly method. Diethyleneamine (DEA) surfactant was used to fabricate the micelle structure of Ba-DEA complex under various DEA concentrations. $BaFe_{12}O_{19}$ powders were synthesized with addition of Fe ions to Ba-DEA complex and then fabricated $BaFe_{12}O_{19}$ powders by spray-pyrolysis process at the temperature range of $800{\sim}1000^{\circ}C$. The molar ratio of Ba/DEA and heat-treatment temperatures significantly affected the magnetic properties and morphology of $BaFe_{12}O_{19}$ powders. $BaFe_{12}O_{19}$ powders synthesized with Ba/DEA molar ratio of 1 and heat-treated at $900^{\circ}C$ showed the coercive forces (iHc) of 4.2 kOe with average crystal size of about 100 nm.

• Composites Research
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• 제26권3호
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• pp.170-174
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• 2013

상온 상압 플라즈마 표면처리된 목분을 폴리프로필렌(polypropylene)과 혼합하였을 때 두 재료의 계면에 미치는 영향을 연구하였다. 목분과 폴리프로필렌을 압출기를 통해 기계적으로 혼합한 후 사출기를 이용하여 목분함유량 50 wt% 목분/폴리프로필렌(Wood Plastic Composite, WPC) 복합재를 제조하였다. 플라즈마 표면처리 공정에 가장 적합한 Monomer(모노머)를 찾기 위해 Oxygen, Benzene, CH-4, Acrylic-acid, Hexafluoroethane, Trifluorotolune, Hexamethyl-disiloxane(HMDSO) 등 7가지의 모노머에 대해 Contact angle(접촉각)을 측정하여 표면에너지를 계산하였다. 그 결과 HMDSO가 가장 높은 표면에너지를 나타내어 플라즈마 공정의 모노머로 적용하였다. 소수성인 폴리프로필렌과 친수성인 목분을 플라즈마 표면처리를 통하여 목분의 표면을 개질하였고 두 재료의 계면 결합력을 향상시킬 수 있었다. 기계적 물성평가 결과는 인장강도의 경우 최대 7.59%, 굴곡강도의 경우 최대 12.43%가 증가하였다. SEM(Scanning Electron Microscope)을 이용하여 파단면을 관찰하였고 플라즈마 표면처리의 효과를 확인하였다.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2001년도 하계학술대회 논문집
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• pp.1080-1083
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• 2001

Ultrafine NiO/YSZ composite powders were prepared by using a glycine nitrate process for anode material of solid oxide fuel cells. The specific surface areas of synthesized NiO/YSZ composite powders were examined with controlling pH of a precursor solution and the content of glycine. The characteristics of synthesized composite powders were examined with X-ray diffractometer, a BET method with N$_2$absorption, scanning and transmission electron microscopy. The strongly acid precursor solution increased the specific surface area of the synthesized composite powders. This is suggested to be caused by the increased binding of metal ions and glycine under a strong acid solution of pH=0.5 that lets glycine consist of mainly the amine group of NH$_3$$\^$+/. After sintering and reducing treatment of NiO/YSZ composite powders synthesized by GNP, the Ni/YSZ pellet showed ideal micro-structure very fine Ni parties of 3-5${\mu}$m were distributed uniformly and fine pores around Ni metal particles were formed, thes, leading to an increase of the triple phase boundary among gas Ni and YSZ.

• Carbon letters
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• 제4권4호
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• pp.168-174
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• 2003

Silver nitrate ($AgNO_3$) powder was mixed into a reformed pitch precursor. Then, the silver-containing pitch was melt spun to form round and "C" shape fibers. A wire mesh was inserted prior to the nozzle to improve the spinnability of the silvercontaining precursor pitch. Silver particles in the carbon fibers (CFs) were detected by XRD and TEM. These tests showed that silver particles were uniformly distributed and the total amount of silver remained constant during stabilization and carbonization. Next, the silver-containing CFs were activated by steam diluted in nitrogen gas. Silver particles accelerated the activation rate, but the specific surface areas of the silver-containing ACFs were similar to those of non-silver containing ACFs at the same burn-off levels. The specific surface area of the C-shaped activated carbon fibers was larger than that of the round activated carbon fibers. The likely reason is that the surface area of a C-shaped CF is about two times larger than that of a round CF when equivalent cross-sectional areas are compared. A small amount of silver particles in the periphery of the CFs was removed during the activation, but the remainder of silver was stayed within the ACFs.

• Bulletin of the Korean Chemical Society
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• 제35권10호
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• pp.2917-2921
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• 2014

Cerium-activated yttrium aluminate ($Y_3Al_5O_{12}:Ce^{3+}$) exhibiting a garnet structure has been widely utilized in the production of light emitting diodes (LEDs) as a yellow emitting phosphor. The commercialized yttrium aluminum garnet (YAG) phosphor is typically synthesized by a solid-state reaction, which produces irregular shape particles with a size of several tens of micrometers by using the top-down method. To control the shape and size of particles, which had been the primary disadvantage of top-down synthetic methods, we synthesized YAG:Ce nanoparticles with a diameter of 500 nm using a coprecipitation method under the atmospheric pressure without the use of template or special equipment. The precursor particles were formed by refluxing an aqueous solution of the nitrate salts of Y, Al, and Ce, urea, and polyvinylpyrrolidone (55 K) at $100^{\circ}C$ for 12 h. YAG:Ce nanoparticles were formed by the calcination of precursor particles at $1100^{\circ}C$ for 10 h under atmospheric conditions. The phase identification, microstructure, and photoluminescent properties of the products were evaluated by X-ray powder diffraction, scanning electron microscopy, absorption spectrum and photoluminescence analyses.