• 한국세라믹학회지
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• 제41권4호
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• pp.340-343
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• 2004

SrA1$_2$O$_4$를 착체중합법으로 합성하는 과정에 있어서 결정의 성장 거동을 연구하였다. 전구체를 900∼100$0^{\circ}C$의 온도범위에서 0∼10시간동안 열처리하였으며, XRD와 TEM을 이용하여 분석하였다 Scherrer's equation을 이용하여 결정자의 크기를 측정하였으며, 그 변화양상을 관찰하였다. 결정자의 크기는 초기 급격한 증가이후 시간의 제곱근에 따라 증가하였으며, 900, 980,그리고 100$0^{\circ}C$의 온도에서 10시간 열처리 이후에 32, 45, 그리고 59nm로 성장하였다. 결정성장속도는 열처리 온도가 증가함에 따라 4.5, 9.4, 그리고 18.6nm/h$^{1}$2/이였다.

• 한국수소및신에너지학회논문집
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• 제32권3호
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• pp.156-162
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• 2021

Mg hydride has a relatively high hydrogen storage amount of 7.6wt%, and inexpensive due to abundant resources, but has high reaction temperature and long reaction time because of treble oxidation reactivity and upper activation energy. Their range of applications could be further extended if their hydrogenation kinetics and degradation behavior could be improved. Therefore, the effect of CaO has improved the hydrogenation kinetics and slowed down the degradation. This study focused on investigating whether to improve the hydrogenation kinetics by synthesizing Mg₂NiH_x-5wt% CaO composites. The Mg₂NiH_x-5wt% CaO composites have been synthesized by hydrogen induced mechanical alloying. The synthesized composites were characterized by performing X-ray diffraction, Scanning Electron Microscopy, Brunauer-Emmett-Teller, Thermogravimetric, and Sivert's type automatic pressure-composition-temperature analysis. Hydriding kinetics were performed using an automatic PCT measurement system and evaluated over the temperature range of 423 K, 523 K, and 623 K. As a result of calculating the hydrogen adsorption amount through the hydrogenation kinetics curve, it was calculated as about 0.42wt%, 0.91wt%, and 1.15wt%, the highest at 623 K and the lowest at 423 K.

• 공업화학
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• 제32권6호
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• pp.690-694
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• 2021

본 연구에서는 글루코스를 전구체로 사용하여 수열합성방법을 통해 구형탄소입자(carbon sphere, CS)를 제조하였다. 200 nm, 500 nm, 1,200 nm 크기의 중공형 TiO₂ (H-TiO₂)는 CS/TiO₂ core-shell 구조를 졸-겔 법과 열처리 방법으로 합성하였다. FE-SEM, HR-TEM, XRD 분석을 통하여 H-TiO₂의 물리적 특성을 측정하였다. H-TiO₂/polyacrylate (PA) 복합체의 UV-Vis-NIR 분석을 통해 색상변화와 일사반사율을 얻었으며, 실험실에서 제작한 차열온도 측정기를 통해 차열온도를 측정하였다. H-TiO₂/PA 복합체는 열전도도가 낮은 건조공기로 채워진 중공구조에 의한 우수한 차열 특성과 근적외선 반사율을 보였다. H-TiO₂/PA 복합체에서 중공구의 크기가 증가함에 따라 열차단 특성이 증가하였다. 1,200 nm 중공 크기의 H-TiO₂를 혼합한 PA 필름에서 측정된 차열온도가 투명 유리판의 차열온도보다 26 ℃ 감소하였다.

• 대한화학회지
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• 제32권6호
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• pp.528-535
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• 1988

이성분 혼합용매 속에서 $[Mo_2O_3(Ox)_2(OxH)_2(NCS)_2]$의 산소고리화 반응에 대한 속도론적 연구는 분광광도법으로 수행되었다. 이 때 온도는 $20^{\circ}C$ 에서 $40^{\circ}C$, 압력은 1bar에서 1500 bar로 변화시켰다. 관찰된 속도 상수는 수소이온 농도의 증가에 따라 증가하고 티오시안이온 농도의 증가에 따라서는 감소한다. 공용매의 유전상수가 증가할수록 더욱 안정한 중간체가 형성된다. 관찰된 속도상수는 $k_{obs}^{-1} = k^{-1} (1 + K^{-1}[H_2O]^{-1})로 주어진다. 모든 활성화파라미터는 양의 값이다. [Mo_2O_3(Ox)_2(OxH)_2(NCS)_2]$의 산소고리화 반응은 Id 메카니즘에 의해 진행된다.

• 대한기계학회논문집B
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• 제23권5호
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• pp.621-627
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• 1999

This paper presents Raman scattering of liquid water to obtain the characteristics with variation of temperature. Very clear Stokes-Raman signals were observed, which shows H-O vibration stretching and H-O-H vibration bending. The obtained spectrum were processed by FFT filter to extract the noise and base. The spectral shape of the H-O stretching provided a various sensitive signature which allowed temperature to be determined by a curve-fitting technique. Those are Maximum Intensity, Maximum Wave Length, FWHM(Full Width at Half Maximum), PMCR(Polymer Monomer Concentration Ratio) and TSIR(Temperature Sensitive Intensity Ratio). TSIR method shows the highest accuracy of $0.1^{\circ}C$ in mean error and $0.32^{\circ}C$ In maximum error.

• Journal of the Korean Wood Science and Technology
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• 제26권3호
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• pp.26-32
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• 1998

The chemical composition of differentiating xylem of Populus deltoides M. were investigated and compared with those from sapwood. The cell wall polysaccharides were extracted sequentially from a differentiating xylem and sugar composition was analyzed with G.L.C, H.P.L.C and gel chromatograpy. The pectin substance and hemicellulose are rich in the cell wall of differentiating xylem. The $H_2O$ extract polysaccharides from differentiating xylem were composed with xylose-glucose residues which seem to be xyloglucan and a pectin. The arabinogalactan and the mannan were extracted with $Na_2CO_3$ solution and also the xylan was extracted with KOH solution. Sugar composition of each fractions in gel filteration of purified $H_2O$ polysaccharide suggests that the xyloglucan can be extracted with $H_2O$ from differentiating xylem.

• 천문학회보
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• 제38권2호
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• pp.32-32
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• 2013

The Korean VLBI Network (KVN) as a world-first multi-frequency VLBI system is operated at four bands of 22, 43, 86, and 129 GHz simultaneously. The performances of both single dish and VLBI network were already confirmed through single dish researches and VLBI evaluation test observations. The VLBI common use of the KVN at 22/43 GHz bands has been started from this autumn. The combined network of KVN and Japanese VERA (KaVA) will start the common use from the first half of next year. Here we present several observational results in the fields of star forming regions, late-type stars, and active galactic nuclei using the KVN and KaVA. The fringes of 44 GHz $CH_3OH$ (Class I) masers were detected from 26 sources for the first time using the KVN and imaging observations are under performing. Simultaneous observations of SiO and $H_2O$ masers toward about 1000 evolved stars showed the different maser properties between SiO and $H_2O$ masers according to the evolutionary stages of AGB and post-AGB stars. The catalog of correlated flux densities were established from a 43 GHz (Q-band) survey of 637 extragalactic sources. At 22 GHz (K-band), flux density measurement and fringe survey for new sources were performed toward a large number of sources. In addition, the large program of KVN and/or KaVA under planning is introduced.

• Bulletin of the Korean Chemical Society
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• 제32권6호
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• pp.1851-1858
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• 2011

Details of the double-bond isomerization of 1-hexene over H-ZSM-5 were clarified using density functional theory. It is found that the reaction proceeds by a mechanism which involves the Br${\o}$nsted acid part of the zeolite solely. According to this mechanism, 1-hexene is first physically adsorbed on the acidic site, and then, the acidic proton transfers to one carbon atom of the double bond, while the other carbon atom of the double bond bonds with the Br${\o}$nsted host oxygen, yielding a stable alkoxy intermediate. Thereafter, the Br${\o}$nsted host oxygen abstracts a hydrogen atom from the $C_6H_{13}$ fragment and the C-O bond is broken, restoring the acidic site and yielding trans-2-hexene. The calculated activation barrier is 12.65 kcal/mol, which is in good agreement with the experimental value. These results well explain the energetic aspects during the course of double-bond isomerization and extend the understanding of the nature of the zeolite active sites.

• 펄프종이기술
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• 제35권1호
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• pp.27-32
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• 2003

To understand the chemical structure of sewer sludge in comparison with commercial compost and charcoal used as a soil improver, it was carried out to analyse their ash contents and metal ions, and to elucidate the chemical structure of their residuals after a sequential treatment of alcohol-benzene(1:2) extraction in Soxhlet, 3% HCl reflux and 79% H₂SO₄ hydrolysis, using CHNS analyzer and solid C-13 NMR spectrometer. The results obtained were as follows: 1. Ash content of sludge was about 46% that is higher than those of compost (17%) and charcoal (4%). 2. The residual of sludge after a sequential treatment of HCl and H₂SO₄ hydrolyses had high ash content about 23%, too. 3. The sludge seems to be suitable to the soil improver because the content of heavy metal ions in sludge was near the compost and below the organic fertilizer standard. 4. Elemental composition of sludge residual after HCl-H₂SO₄ hydrolyes was C/sub 56/H/sub 91/O/sub 12/N₂S = (C/sub 6/H/sub 10/O/sub 5/)/sub 7/(C/sub 6/H₄)/sub 7/C₂H/sub 43/O₂N₂S, similar to C/sub 103/H/sub 122/O/sub 33/N/sub 6/S = (C/sub 6/H/sub 10/O/sub 5/)/sub 6/(C/sub 6/H₄)/sub 10/C/sub 7/H/sub 22/O₃N/sub 6/S of compost. 5. The sludge residual had proved to have both considerable aliphatic and aromatic groups, but the compost residual to have mainly aliphatic groups and the charcoal to have mainly aromatic groups, through the peak analysis of solid C-13 NMR charts. 6. So, the sewer sludge is proved to have a considerable amount of aromaticity like in woody biomass containing lignin.

• 한국물환경학회지
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• 제32권1호
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• pp.46-51
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• 2016

In this study, we synthesized a combination of graphene oxide (GO) and titanium dioxide (TiO₂) and confirm that GO can be used for CO₂ photoreduction. TiO₂ exhibited highly efficient combination with other conventional electric charges generated by these paration phenomenon for suppression of hole-electron recombination. This improved the efficiency of CO₂ photoreduction. The synthetic form of GO-TiO₂ used in this study was agraphene sheet surrounded by TiO₂ powder. Efficiency and stability were enhanced by combination of GO and TiO₂. In a CO₂ photoreduction experiment, the highest CO conversion rate was 0.652 μmol/g·h in GO10-TiO₂ (2.3-fold that of pure TiO₂) and the highest CH₄ production rate was 0.037 μmol/g·h in GO0.1-TiO₂ (2.4-fold that of pure TiO₂). GO enhances photocatalytic efficiency by functioning as a support and absorbent, and enabling charge separation. With increasing GO concentration, the CH₄ level decreases to~45% due to decreased transfer of electrons. In this study, TiO₂ together with GO yielded a different result than the normal doping effect and selective CO₂ photoreduction.