• Journal of the Korean Ceramic Society
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• v.52 no.3
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• pp.173-179
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• 2015

We report the facile synthesis of graphene-$CdLa_2S_4$ composite through a facile solvothermal method at low temperature. The as-prepared products were characterized by X-ray diffraction (XRD) and by Scanning electron microscopy (SEM) with energy dispersive X-ray (EDX) analysis and BET analysis, revealing the uniform covering of the graphene nanosheet with $CdLa_2S_4$ nanocrystals. The as-prepared samples show a higher efficiency for the photocatalytic degradation of typical MB dye compared with P25 and $CdLa_2S_4$ bulk nanoparticles. The enhancement of visible-light-responsive photocatalytic properties by decolorization of Rh.B dye may be attributed to the following causes. Firstly, graphene nanosheet is capable of accepting, transporting and storing electrons, and thus retarding or hindering the recombination of the electrons with the holes remaining on the excited $CdLa_2S_4$ nanoparticles. Secondly, graphene nanosheet can increase the adsorption of pollutants. The final cause is that their extended light absorption range. This work not only offers a simple way to synthesize graphene-based composites via a one-step process at low temperature but also a path to obtain efficient functional materials for environmental purification and other applications.

• Journal of Environmental Science International
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• v.14 no.12
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• pp.1093-1102
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• 2005

Effects of abscisic acid(ABA) and temperature on the anthocyanin accumulation and phenylalanine ammonia Iyase(PAL) activity were investigated in seedlings of Arabidopsis thaliana. In time course study, exogenous application of ABA $(50-1000\;{\mu}M)$ led to a noticeable increase in anthocyanin pigments which persisted over the following 5 days. Anthocyanins increased in concert with the chlorophyll loss. The activity of PAL, a key enzyme in the phenylpropanoid pathway, increased on exposure to ABA and reached maximum on the 4th day, This result shows that anthocyanin synthesis and PAL activity have a close physiological relationships. In the effects of temperatures ($10^{\circ}C,\;17^{\circ}C,\;25^{\circ}C$and $30^{\circ}C$) on anthocyanin accumulation and PAL activity in seedlings, a moderate-low temperatures ($17^{\circ}C$) enhanced both anthocyanin content and PAL activity, whereas elevated temperatures ($30^{\circ}C$) showed low levels of anthocyanin and PAL activity, suggesting a correlation between temperature-induced anthocyanin synthesis and the accumulation of PAL mRNA. Simultaneous application of ABA with temperatures Induced higher anthocyanin synthesis and PAL activity in seedlings than ABA or temperature stress alone. Moderate-low temperature with ABA exposure elicited the maximal induction of anthocyanin synthesis and PAL activity. Therefore, ABA treatment significantly increased thermotolerance in .A. thalinan seedlings. Ethephon and ABA showed similar mode of action in physiological effects on anthocyanin accumulation and PAL activity. Our data support that anthocyanins may be protective in preventing damage caused by environmental stresses and play an important role in the acquisition of freezing tolerance.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.11a
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• pp.395-395
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• 2008

Water-assisted synthesis of carbon nanotubes (CNTs) has been intensively studied in recent years, reporting that water vapor enhances the activity and lifetime of metal catalyst for the CNT growth. While most of these studies has been focused on the supergrowth of CNTs at high temperature, rarely has the similar approach been made for the CNT synthesis at low temperature. Since the metal catalyst are much less active at lower temperature, we expect that the addition of water vapor may increase the activity of catalyst more largely at lower temperature. We synthesized multi-walled CNTs at temperature as low as $360^{\circ}C$ by introducing water vapor during growth. The water addition caused CNTs to grow ~3 times faster. Moreover, the water-assisted growth prolonged the termination of CNT growth, implying the enhancement of catalyst lifetime. In general, a thinner catalyst layer is likely to produce smaller-diameter, longer CNTs. In a similar manner, the water vapor had a greater effect on the growth of CNTs for a smaller thickness of catalyst in this study. To figure out the role of process gases, CNTs were grown in the first stage and then exposed to each of process gases in the second stage. It was shown that water vapor and hydrogen did not etch CNTs while acetylene led to the additional growth of CNTs even faster in the second stage. As-grown CNTs were characterized by scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), atomic force microscopy (AFM), and Raman spectroscopy.

• Tribology and Lubricants
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• v.37 no.2
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• pp.62-70
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• 2021

The problem with intermetallics coating using the heat of molten casting is that the heat generated during combustion synthesis dissolves the coating and the substrate metal. This study investigates whether pre-annealing before synthesis can control the reaction heat, with the aim of Ni₃Al coating on the casting surface. Therefore, the effects of the annealing temperature and time on the combustion synthesis behavior of the powder compact of Ni-25at%Al after annealing were investigated. As results, the reaction heat when synthesized decreased as the annealing temperature was high and the annealing time was longer. This was attributed to the fact that Al was diffused to Ni particles during low temperature annealing and intermediate Ni-Al compounds were formed during high temperature annealing. After combustion synthesis, however, it was found that their microstructures were almost identical except for the amount of intermediate intermetallics. Furthermore, an annealing temperature above 450℃, at which intermediate compounds begin to form, is needed to prevent the dissolving problem during synthesizing. The intermetallics synthesized after annealing at higher temperature and prolonger annealing time showed a good wear resistance. This might be because much intermediate intermetallics of high hardness were remained in the microstructure.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.27 no.12
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• pp.852-856
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• 2014

$BaTiO_3$ nano powder can be synthesized by hydrate salt method at $120^{\circ}C$ in air. Decreasing the thickness of thick film, the nano dielectric particle is needed in electronic ceramics. However, the synthesis of $BaTiO_3$ nano particle at low temperature in air and their mechanism were not reported enough. And ultrasonic treatment can be tried because of low temperature process in air. Therefore, in this study, the $BaTiO_3$ nano powder was synthesised with the synthesis time and ultrasonic treatment at $120^{\circ}C$ in air. In the synthesis process, the effects of process were evaluated. From the experimental observation, the synthesis mechanism was proposed. The homogeneous $BaTiO_3$ particle was synthesised by KOH salt solution at $120^{\circ}C$ for 1hour. It was conformed that the ultrasonic treatment effected on the increase of synthesis rate. After cutting the salt powder using FIB, $BaTiO_3$ nano particles observed homogeneously in the cross-section of the salt particle.

• Bulletin of the Korean Chemical Society
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• v.32 no.1
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• pp.141-144
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• 2011

We report the synthesis of $SrTiO_3$, $BaTiO_3$ and $Ba_xSr_{1-x}TiO_3$ (BST) nanoparticles (NPs) in various compositions (x = 0.25, 0.5 and 0.75) by an inorganic sol-gel method under a basic condition. Highly crystalline nanoparticles were formed at the reaction temperature of 25 - $100^{\circ}C$ from a stabilized titanium alkoxide in tetramethylammonium hydroxide (TMAH) and barium or strontium acetate in aqueous solution. Morphology and particle structure of the synthesized BST NPs were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and transmission electron microscopy (TEM). The BST nanoparticles in various compositions were monodispersed without mutual aggregation, and their average sizes were in the range of 70 - 80 nm. Furthermore, they showed highly crystallized perovskite phase over the whole composition range from $SrTiO_3$ to $BaTiO_3$. We also proposed a mechanism for the low-temperature formation of BST NPs.

• Archives of Pharmacal Research
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• v.26 no.10
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• pp.840-845
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• 2003

Temperature change is one of the major environmental factors that influence the human skin. However, the relationship between temperature and melanogenesis has received little attention. In the present study, we investigated the effects of temperature change on melanogenesis in a mouse melanocyte cell line (Mel-Ab), and primary cultured human melanocytes. We found that Mel-Ab cells cultured at low temperatures (31 and 34$^{\circ}C$) produce less melanin than cells at 37$^{\circ}C$. These results were confirmed by experiments upon human melanocytes, demonstrating that the hypopigmenting effect of low temperatures is not cell type dependent. The observed melanin production was found to be accompanied by tyrosinase activity at each temperature, indicating that tyrosinase activity is regulated by temperature. We further examined whether the incubation period at low temperatures plays an important role in the regulation of melanogenesis. Short exposures to 27$^{\circ}C$ for 1 h or 3 h did not affect tyrosinase activity or melanin synthesis, whereas long exposures to 31$^{\circ}C$ for 2 days or 6 days significantly reduced tyrosinase activity and melanin synthesis in a duration-dependent manner. Our results suggest that exposure to low temperature and the duration of this exposure are important regulators of melanogenesis.

• The Korean Journal of Ceramics
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• v.2 no.4
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• pp.221-225
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• 1996

In diamond synthesis by metal film growth method under high pressure and high temperature, the nucleation and growth of diamond was observed dependent on the carbon source variation from graphite powder to the heat treated powders of lamp black carbon. At the low driving force condition near equilibrium pressure and temperature line, nucleation of diamond did not occur but growth of seed diamond appeared in the synthesis from lamp black carbon while both nucleation and growth of diamond took place in the synthesis from graphite. Growth morphology change of diamond occurred from cubo-octahedron to octahedron in the synthesis from graphite but very irregular growth of seed diamond occurred in the synthesis from lamp block carbon. Lamp black carbon transformed to recrystallized graphite first and very nucleation of diamond was observed on the recrystallized graphite surface. Growth morphology of diamond on the recrystallized graphite was clear cubo-octahedron even at higher pressure departure condition from equilibrium pressure and temperature line.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.248-248
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• 2012

Synthesis graphene on Cu substrate by plasma-enhanced chemical vapor deposition (PE-CVD) is investigated and its quality's affection factors are discussed in this work. Compared with the graphene synthesized at high temperature in chemical vapor deposition (CVD), the low-temperature graphene film by PE-CVD has relatively low quality with many defects. However, the advantage of low-temperature is also obvious that low melting point materials will be available to synthesize graphene as substrate. In this study, the temperature will be kept constant in $400^{\circ}C$ and the graphene was grown in plasma environment with changing the plasma power, the flow rate of precursors, and the distance between plasma generator coil and substrates. Then, we investigate the effect of temperature and the influence of process variables to graphene film's quality and characterize the film properties with Raman spectroscopy and sheet resistance and optical emission spectroscopy.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.421-421
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• 2012

Graphene has drawn enormous attention owing to its outstanding properties, such as high charge mobility, excellent transparence and mechanical property. Synthesis of Graphene by chemical vapor deposition (CVD) is an attractive way to produce large-scale Graphene on various substrates. However the fatal limitation of CVD process is high temperature requirement(around $1,000^{\circ}C$), at which many substrates such as Al substrate cannot endure. Therefore, we propose plasma enhanced CVD (PECVD) and decrease the temperature to $400^{\circ}C$. Fig. 1 shows the typical structure of RF-PECVD instrument. The quality of Graphene is affected by several variables. Such as plasma power, distance between substrate and electronic coil, flow rate of source gas and growth time. In this study, we investigate the influence of these factors on Graphene synthesis in vacuum condition. And the results were checked by Raman spectra and conductivity measurement.