• Nuclear Engineering and Technology
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• 제27권2호
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• pp.216-225
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• 1995

TBP 유기상으로 부터 질산용액으로 U(VI)의 물질 이동과 그 질산용액에서 U(VI)의 U(IV)으로 전해 환원과정을 갖는 두 상으로 구성된 계에서 U(IV)을 전해적인 방법으로 생산하기 위해 필요한 기본설계 자료로서의 운전조건 및 전극면적 계산을 위한 계의 수치해석이 수행되었다. 효과적인 U(IV)의 생산수율을 위해서는 적절한 물질전달 면적을 유지시키는 것이 전극면적을 증가시키는 것보다 중요하였으며, 전극면적과 운전시 간은 최종 수용액의 U(IV) 조성에 큰 영향을 주는 것을 알 수 있었다 또한 여러 계의 조건에서 최종 용액의 U(IV) 생산 조건을 만족시키기 위한 최적 전극면적이 계산되었다. 수용상의 최적 질산 농도는 U(IV) 생산만을 위해서는 약 0.37M이나, 용액중의 U(IV)의 가수분해를 방지하기 위해 최소한 0.5M을 유지해야 함을 알 수 있었다.

• 대한화학회지
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• 제30권5호
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• pp.475-482
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• 1986

$Ni^{2+}$와 D-penicillamine사이의 착물형성반응에 대한 반응속도 및 평형에 관한 수용액중에서 실시하였다. 속도론적 실험은 압력-급변법을 사용하여 pH8~9범위에서 실시하였다. D-Penicillamine은 질소와 유황원자를 주게로 하여 pH＞9.2조건에서 $Ni^{2+}$이온에 배위하나 pH값 8.25∼9.07범위에서 총괄 안정도 상수값이 급격히 감소하며 비해리된 mercapto기가 결합에 참여하지 않는 것으로 밝혀졌다. 또한 이 착물 형성반응에 있어 율속단계는 $Ni^{2+}$이온의 내부 배위권으로 부터 물분자가 유리되는 과정임이 밝혀졌다.

• Bulletin of the Korean Chemical Society
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• 제23권1호
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• pp.35-40
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• 2002

Photoreaction of guest organic anions in layered organic-inorganic hybrid materials was investigated. The layered hybrids were synthesized by an anion-exchange reaction of $[LiAl_2(OH)_6]Cl{\cdot}yH_2O$ layered double hydroxide with aqueous (Z,Z)- and (E,E)-muconates under inert atmospheric condition, to give new organicinorganic hybrids of $[LiAl_2(OH)_6]_2[(Z,Z)-C_6H_4O_4]{\cdot}zH_2O$ and $[LiAl_2(OH)_6]_2[(E,E)-C_6H_4O_4]{\cdot}H_2O$, respectively. The basal spacings calculated by XRPD of intercalates indicate that muconate anions have almost vertical arrangements against the host $[LiAl_2(OH)_6]^+$ lattices in the interlayer of organic-inorganic hybrid materials. When UV light was irradiated on the suspension of $[LiAl_2(OH)_6]_2[(Z,Z)-C_6H_4O_4]{\cdot}zH_2O$, the (Z,Z)-muconate anions of the gallery space of hybrids were polymerized in the aqueous media while it was isomerized into more stable (E,E)-muconate in the methanollic suspension in the presence of catalytic amount of molecular iodine. All the products were characterized using elemental analysis, TGA, XRPD, FT-IR, $^1H$ NMR and $^{13}C$ CP-MAS NMR.

• Bulletin of the Korean Chemical Society
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• 제33권8호
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• pp.2546-2552
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• 2012

A novel biguanide-functionalized $Fe_3O_4/SiO_2$ magnetite nanoparticle with a core-shell structure was developed for utilization as a heterogeneous organosuperbase in chemical transformations. The structural, surface, and magnetic characteristics of the nanosized catalyst were investigated by various techniques such as transmission electron microscopy (TEM), powder X-ray diffraction (XRD), vibrating sample magnetometry (VSM), elemental analyzer (EA), thermogravimetric analysis (TGA), $N_2$ adsorption-desorption (BET and BJH) and FT-IR. The biguanide-functionalized $Fe_3O_4/SiO_2$ nanoparticles showed a superpara-magnetic property with a saturation magnetization value of 46.7 emu/g, indicating great potential for application in magnetically separation technologies. In application point of view, the prepared catalyst was found to act as an efficient recoverable nanocatalyst in nitroaldol and domino Knoevenagel condensation/Michael addition/cyclization reactions in aqueous media under mild condition. Additionally, the catalyst was reused six times without significant degradation in catalytic activity and performance.

• 설비공학논문집
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• 제9권2호
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• pp.144-152
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• 1997

Film absorption involves simultaneous heat and mass transfer in the vapor-liquid system. In the present work, the absorption process of water vapor by an aqueous soluton of LiBr flowing inside of the vertical tube was investigated. The continuity, momentum, energy and diffusion equations for the solution film and vapor were formulated in integral forms and solved numerically. The model could predict the film thickness, the pressure gradient, and the heat and mass transfer rate. Particularly the effects of vapor flow conditions on the absorption process were investigated in terms of the vapor Reynolds number. As the vapor Reynolds number increased, the shear stress at the vapor-solution interface also increased. Consequently solution film became thinner at higher vapor flowrate under the co-currentflow condition. Thinner film was capable of higher heat transfer to the wall and leaded to higher absorption rate of the water vapor into the solution film.

• Advances in nano research
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• 제9권1호
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• pp.59-67
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• 2020

Filter cake formation during rotary drilling operation is an unavoidable scenario, hence there is need for constant improvement in the approaches used in monitoring the cake thickness growth in order to prevent drill-string sticking. This study proposes an improved model that predicts the growth of mud cake thickness overtime with the consideration of the addition of nanoparticles in the formulated drilling fluid system. Ferric oxide, titanium dioxide and copper oxide nanoparticles were used in varying amounts (2 g, 4 g and 6 g), and filtration data were obtained from the HPHT filtration test. The filter cakes formed were further analyzed with scanning electron microscope to obtain the morphological characteristics. The data obtained was used to validate the new filtrate loss model. This model specifically presents the concept of time variation in filter cake formation as against the previous works of constant and definite time. Regression coefficient which is a statistical measure was used to validate the new model and the predicted results were compared with the API model. The new model showed R² values of 99.9%, and the predictions from the proposed filtration model can be said to be more closely related to the experimental data than that predicted from the API model from the SSE and RMSE results.

• KSBB Journal
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• 제17권3호
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• pp.314-316
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• 2002

염소계 소독제인 TICA (Trichloro isocyanuric acid)와 calcium hypochlorite에 의한 대장균의 사멸특성을 비교하기 위하여, 접촉시간과 소독제의 농도를 달리 하여 소독력을 측정하였다. 소독제의 농도는 4∼16 ppm으로 하고 접촉시간은 30sec, 1, 2, 4, 8 min으로 하여 각각 측정하였다. TICA 12 ppm에서 4초만에 90%의 대장균이 사멸하였다. 하지만 calcium hypochlorite 12 ppm에서는 390초 동안 접촉시켜야 같은 사멸효과를 얻을 수 있었다. 또한 햇빛에 의한 소독력의 감소를 측정한 결과 TICA는 햇빛에 6시간동안 노출되어도 소독력이 유지되었으나, calcium hypochlorite는 햇빛에 1시간만 노출되어도 소독력이 급격히 감소하기 시작하여 4시간만에 소독력을 완전히 상실하였다. 본 실험조건 하에서는 TICA가 calcium hypo-chlorite보다 대장균에 대한 사멸률 및 소독지속력이 모두 우수하게 측정되었으며, 또한 본 연구결과로부터 동일한 소독 효과를 얻기 위한 소독제별 최적조건을 비교 제시하였다.

• Journal of Welding and Joining
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• 제21권4호
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• pp.39-45
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• 2003

Nano-TiO$_2$ photocatalytic coatings were deposited on the stainless steel 304(50$\times$70$\times$3mm) by the APS(Atmospheric Plasma Spraying). Photocatlytic reaction was tested in MB(methylene blue) aqueous solution. For applying nano-TiO$_2$ powders by thermal spray, the starting nano-TiO$_2$ powder with 100% anatase crystalline was agglomerated by spray drying. Plasma second gas(H$_2$) flow rate and spraying distance were used as principal process parameters which are known to control heat enthalpy(heat input). The relationship between process parameters and the characteristics of microstructure such as the anatase phase fraction and grain size of the TiO$_2$ coatings were investigated. The photo-decomposition efficiency of TiO$_2$ coatings was evaluated by the kinetics of MB aqueous solution decomposition. It was found that the TiO$_2$ coating with a lower heat input condition had a higher anatase fraction, smaller anatase grain size and a better photo-decomposition efficiency.

• Journal of the Korean Wood Science and Technology
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• 제48권2호
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• pp.231-244
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• 2020

As a way of finding value-added materials from waste medium density fiberboard (MDF), this study characterized cellulose nanocrystals (CNCs) isolated by ammonium persulfate (APS) oxidation using recycled MDF fibers. Chemical composition of the recycled MDF fibers was done to quantify α-cellulose, hemicellulose, lignin, nitrogen, ash and extractives. The APS oxidation was performed at 60 ℃ for 16 h, followed by ultrasonication, which resulted in a CNC yield of 11%. Transmission electron microscope images showed that rod-like CNCs had an average length and diameter of 167±47 nm and 8.24±2.28 nm, respectively, which gave an aspect ratio of about 20. The conductometric titration of aqueous CNCs suspension resulted in a carboxyl content of 0.24 mmol/g and the degree of oxidation was 0.04. Attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy clearly showed the presence of carboxyl group on the CNCs prepared by the APS oxidation. The change of pH of the aqueous CNC suspension from 4 to 7 converted the carboxyl group to sodium carboxylate group. These results showed that the APS oxidation was facile and CNCs had a one-step preparation method, and thus suggested an optimization of the oxidation condition in future.

• Environmental Engineering Research
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• 제10권4호
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• pp.174-180
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• 2005

Nano-sized iron was synthesized using borohydride reduction of $Fe^{3+}$ in aqueous solution. A wide range of synthesis conditions including varying concentrations of reagents, reagent feeding rate, and solution pH was applied in an aqueous system under anaerobic condition. The reactivity of nano-sized iron from each synthesis was evaluated by reacting the iron with TCE in batch systems. Evidence obtained from this study suggest the reactivity of iron is strongly dependent on the synthesis solution pH. The iron reactivity increased as solution pH decreased. More rapid TCE reduction was observed for iron samples synthesized from higher initial $Fe^{3+}$ concentration, which resulted in lower solution pH during the synthesis reaction. Faster feeding of $BH_4^-$ solution to the $Fe^{3+}$ solution resulted in lower synthesis solution pH and the resultant iron samples gave higher TCE reduction rate. Lowering the pH of the solution after completion of the synthesis reaction significantly increased reactivity of iron. It is presumed that the increase in the reactivity of iron synthesized at lower pH is due to less precipitation of iron (hydr)oxides or less surface passivation of iron.