• Bulletin of the Korean Chemical Society
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• 제33권2호
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• pp.403-408
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• 2012

In this study, the homogenous Pd nanoparticles (Pd NPs) were first prepared with bayberry tannin (BT) as the stabilizers. Subsequently, the obtained bayberry tannin-stabilized Pd nanoparticles (BT-Pd) were immobilized onto ${\gamma}-Al_2O_3$ to prepare heterogeneous ${\gamma}-Al_2O_3$-BT-Pd catalysts. Fourier Transformation Infrared Spectrum (FTIR) and X-ray Photoelectron Spectroscopy (XPS) analyses confirmed that the Pd NPs were well stabilized by the phenolic hydroxyl groups of BT. Transmission Electron Microscopy (TEM) observation indicated that the diameter of the Pd NPs can be effectively controlled in the range of 4.2-16.0 nm by varying the amount of BT. It is found that the ${\gamma}-Al_2O_3$-BT-Pd catalysts exhibit highly activity for various olefin hydrogenations. For example, the initial TOF (turnover frequency) of the ${\gamma}-Al_2O_3$-BT-Pd in the allyl alcohol hydrogenation is as high as $12804 mol{\cdot}mol^{-1}{\cdot}h^{-1}$. Furthermore, the ${\gamma}-Al_2O_3$-BT-Pd can be reused 5 times without significant loss of activity, exhibiting a superior reusability as compared with conventionally prepared ${\gamma}-Al_2O_3$-Pd catalysts.

• 대한기계학회논문집B
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• 제36권5호
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• pp.509-515
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• 2012

본 논문은 수소를 연료로 하는 확산화염을 이용하여 알루미나 나노입자를 합성할 때, 합성되는 알루미나 나노입자의 특성에 미치는 화염온도의 영향을 조사하였다. 합성된 나노입자의 특성을 전자현미경 이미지, 결정구조 분석, 비표면적과 기공의 크기 분석, 화염온도 측정 등의 여러 특성분석 방법으로 조사하였다. 사용된 화염의 중심축 최고온도는 산화제의 산소농도가 19, 21, 30, 47%인 각각의 실험조건에서 1507.8K, 1593.8K, 1753.1K, 1998.7K으로 측정되었다. SEM 이미지 분석 및 BET 비표면적 측정을 통해서는 47% 산소농도인 경우에는 50 nm 수준의 독립적인 구형입자가 생성되었음을 확인할 수 있었으며, 19%와 21%의 경우에는 응집된 상태의 20-30 nm 수준의 입자를 볼 수 있었다. XRD 결과에서는 감마(${\gamma}$)-알루미나가 주를 이루는 것으로 판단되었다. 이상의 결과를 바탕으로 촉매 담체로 사용하기 위한 알루미나 나노입자를 연소합성 하기 위한 가장 적절한 조건으로 실험했던 네 경우 중에서는 산화제의 산소농도가 21%인 두 번째 경우를 선택할 수 있었다.

• Structural Engineering and Mechanics
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• 제85권1호
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• pp.29-53
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• 2023

High-strength shielding concrete against gamma radiation is a priority for many medical and industrial facilities. This paper aimed to investigate the gamma-ray shielding properties of high-strength hematite concrete mixed with silica fume (SF) with nanoparticles of lead dioxide (PbO₂), tungsten oxide (WO₃), and bismuth oxide (Bi₂O₃). The effect of mixing steel fibres with the aforementioned binders was also investigated. The reference mixture was prepared for high-strength concrete (HSCC) containing 100% hematite coarse and fine aggregate. Thirteen mixtures containing 5% SF and nanoparticles of PbO₂, WO₃, and Bi₂O₃ (2%, 5%, and 7% of the cement mass, respectively) were prepared. Steel fibres were added at a volume ratio of 0.28% of the volume of concrete with 5% of nanoparticles. The slump test was conducted to workability of fresh concrete Unit weight water permeability, compressive strength, splitting tensile strength, flexural strength, and modulus of elasticity tests were conducted to assess concrete's engineering properties at 28 days. Gamma-ray radiation of 137Cs emits photons with an energy of 662 keV, and that of 60Co emits two photons with energies of 1173 and 1332 keV were applied on concrete specimens to assess radiation shielding properties. Nanoparticles partially replacing cement reduced slump in workability of fresh concrete. The compressive strength of mixtures, including nanoparticles was shown to be greater, achieving 94.5 MPa for the mixture consisting of 7.5 PbO2. In contrast, the mixture (5PbO₂-F) containing steel fibres achieved the highest values for splitting tensile, flexural strength, and modulus of elasticity (11.71, 15.97, and 42,840 MPa, respectively). High-strength shielded concrete (7.5PbO2) showed the best radiation protection. It also showed the minimum concrete thickness required to prevent the transmission of radiation.

• 한국재료학회지
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• 제22권4호
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• pp.195-201
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• 2012

$Ce^{3+}$-doped yttrium aluminum gallium garnet (YAGG:$Ce^{3+}$), which is a green-emitting phosphor, was synthesized by solid state reaction using ${\alpha}$-phase or ${\gamma}$-phase of nano-sized $Al_2O_3$ as the Al source. The processing conditions and the chemical composition of phosphor for the maximum emission intensity were optimized on the basis of emission intensity under vacuum UV excitation. The optimum heating temperature for phosphor preparation was $1550^{\circ}C$. Photoluminescence properties of the synthesized phosphor were investigated in detail. From the excitation and emission spectra, it was confirmed that the YAGG:$Ce^{3+}$ phosphors effectively absorb the vacuum UV of 120-200 nm and emit green light positioned around 530 nm. The crystalline phase of the alumina nanoparticles affected the particle size and the luminescence property of the synthesized phosphors. Nano-sized ${\gamma}-Al_2O_3$ was more effective for the achievement of higher emission intensity than was nano-sized ${\alpha}-Al_2O_3$. This discrepancy is considered to be because the diffusion of $Al^{3+}$ into $Y_2O_3$ lattice is dependent on the crystalline phase of $Al_2O_3$, which affects the phase transformation of YAGG:$Ce^{3+}$ phosphors. The optimum chemical composition, having the maximum emission intensity, was $(Y_{2.98}Ce_{0.02})(Al_{2.8}Ga_{1.8})O_{11.4}$ prepared with ${\gamma}-Al_2O_3$. On the other hand, the decay time of the YAGG:$Ce^{3+}$ phosphors, irrespective of the crystalline phase of the nano-sized alumina source, was below 1 ms due to the allowed $5d{\rightarrow}4f$ transition of the $Ce^{3+}$ activator.

• 공업화학
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• 제30권2호
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• pp.151-154
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• 2019

코디어라이트 허니컴 표면에 알루미나 워시코트 지지체를 형성시키고 비교적 단순한 건식 코팅 공정으로 산화철 촉매를 코팅함으로써 실제 환경에 효과적으로 적용이 가능한 모노리스 구조 촉매를 제조하였다. 허니컴 통로 벽 구석으로 형성된 워시코트 알루미나 미세 기공으로 균일하게 코팅된 산화철 촉매를 확인하였으며, 일산화탄소 산화 반응에 적용하기 위하여 산화철 촉매의 열처리 효과를 검증하였다. $350^{\circ}C$ 부근에서 열처리한 산화철 촉매가 가장 우수한 촉매 성능을 발휘하였고, $200^{\circ}C$ 이상의 온도 영역에서 100% 전환율을 나타내었다.

• Korean Chemical Engineering Research
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• 제61권2호
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• pp.226-233
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• 2023

To create an environmentally sustainable fuel with a low sulfur concentration, requires alternative sulfur removal methods. During the course of this study, a high surface gamma alumina-supported ZnO nanocatalyst with a ZnO/-Al₂O₃ ratio of 12% was developed and tested for its ability to improve the activity of the oxidative desulfurization (ODS) process for the desulfurization of kerosene fuel. Scanning electron microscopy (SEM) and Brunauer-Emmett-Teller (BET) were used to characterize the produced nanocatalyst. In a digital batch baffled reactor (20~80 min), the effectiveness of the synthesized nanocatalyst was tested at different initial concentrations of dibenzothiophene (DBT) of 300~600 ppm, oxidation temperatures (25~70 ℃), and oxidation periods (0.5, 1, and 2 hours). The baffles included in the digital baffled batch reactor resist the swirling of the reaction mixture, thus facilitating mixing. The ODS procedure yielded the maximum DBT conversion (95.5%) at 70 ℃ with an 80-minute reaction time and an initial DBT level of 600 ppm. The most precise values of kinetic variables were subsequently determined using a mathematical modelling procedure for the ODS procedure. The average absolute error of the simulation findings was less than 5%, demonstrating a good degree of agreement with the experimental results acquired from all runs. The optimization of the operating conditions revealed that 99.1% of the DBT can be removed in 140 minutes.

• 공업화학
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• 제28권3호
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• pp.351-354
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• 2017

역미셀법을 이용하여 열적 안정성이 우수한 감마-알루미나의 합성 공정을 최적화하기 위하여 실험계획법을 사용하였다. 먼저 합성공정에 주 요소인 계면활성제, 물 및 오일의 비에 대한 최적의 실험조건을 설계하기 위하여 혼합물 실험법을 이용하여 12가지 실험조건을 도출하였다. 설계된 조건에서 역미셀법을 이용하여 합성한 입자를 $900^{\circ}C$에서 소성한 결과 입자의 크기에 차이는 있었지만 모두 감마-알루미나 결정구조를 가졌다. 도출된 실험결과를 이용하여 계산된 2차 회귀모델의 결정계수는 93.68%이었으며, P- 값이 0.002로서 유의하다고 할 수 있다. 다양한 입자크기를 가지는 감마-알루미나의 합성조건을 모든 범위에서 대하여 표면도와 등고선도를 이용하여 제시하였다. 그 결과 Surfactant/Water/Oil의 질량비가 0.3450/0.0729/0.5821인 조건에서 합성할 때 약 2.8 nm의 가장 작은 입자가 합성되는 것으로 계산되었다.

• Nuclear Engineering and Technology
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• 제55권5호
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• pp.1519-1526
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• 2023

For the first time Aluminium-BariumeZinc oxide nanocomposite (ZABONC) was synthesized by solution combustion method where calcination was carried out at low temperatures (600℃) to study the electromagnetic (EM) (X/γ) radiation shielding properties. Further for characterization purpose standard techniques like PXRD, SEM, UV-VISIBLE, FTIR were used to find phase purity, functional groups, surface morphology, and to do structural analysis and energy band gap determination. The PXRD pattern shows (hkl) planes corresponding to spinel cubic phase of ZnAl₂O4, cubic Ba(NO₃)₂, α and γ phase of Al₂O₃ which clearly confirms the formation of complex nano composite. From SEM histogram mean size of nano particles was calculated and is in the order of 17 nm. Wood and Tauc's relation direct energy band gap calculation gives energy gap of 2.9 eV. In addition, EM (X/γ) shielding properties were measured and compared with the theoretical ones using standard procedures (NaI (Tl) detector and multi channel analyzer MCA). For energy above 356 keV the measured shielding parameters agree well with the theory, while below this value slight deviation is observed, due to the influence of atomic/crystallite size of the ZABONC. Hence synthesized ZABONC can be used as a shielding material in EM (X/γ) radiation shielding.

• Bulletin of the Korean Chemical Society
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• 제25권5호
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• pp.687-693
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• 2004

Composite membranes with a titania layer were prepared by soaking-rolling method with the titania sol of nanoparticles formed in the sol-gel process and investigated regarding the vapor permeation of various organic mixtures. The support modification was conducted by pressing $SiO_2$ xerogel of 500 nm in particle size under 10 MPa on the surface of a porous stainless steel (SUS) substrate and designed the multi-layered structure by coating the intermediate layer of ${\gamma}-Al_2O_3$. Microstructure of titania membrane was affected by heat-treatment and synthesis conditions of precursor sol, and titania formed at calcination temperature of 300$^{\circ}C$ with sol of [$H^+$]/[TIP]=0.3 possessed surface area of 210 $m^2$/g, average pore size of 1.25 nm. The titania composite membrane showed high $H_2/N_2$ selectivity and water/ethanol selectivity as 25-30 and 50-100, respectively. As a result of vapor permeation for water-alcohol and alcohol-alcohol mixture, titania composite membrane showed water-permselective and molecular-sieve permeation behavior. However, water/methanol selectivity of the membrane was very low because of chemical affinity of permeants for the membrane by similar physicochemical properties of water and methanol.

• Korean Chemical Engineering Research
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• 제49권5호
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• pp.664-668
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• 2011

500 mL 교반탱크반응기 내에서 $AlCl_3$ 증기를 $H_2O$ 증기에 의해 부분 가수분해시켜 30~200 nm 크기의 $AlO_xCl_y(OH)_z$로 표시되는 구형의 알루미나 전구체 입자를 제조하였다. 반응시간, 교반속도, 반응온도가 생성된 입자의 형상, 크기 등에 미치는 영향을 조사하였다. 반응시간을 20, 60, 300 s로 변화시킨 결과 생성 입자의 형상 및 크기에 별다른 차이가 없었으며, 교반속도를 0, 300, 800 rpm으로 변화시킨 결과 0 rpm에서 입자의 크기가 최대값을 보였고, 반응온도를 180, 190, 200, $240^{\circ}C$로 변화시킨 결과 $190^{\circ}C$에서 제조된 입자의 크기가 가장 작게 나타났다. 가수분해 생성물 입자를 $10^{\circ}C$/min의 속도로 $1,200^{\circ}C$까지 가열하고 6 시간동안 하소시켜 45 nm 크기의 ${\alpha}$ 알루미나 입자를 얻었다. 하소과정에서 인접입자 사이의 소결에 의해 입자 형상이 구형에서 벌레모양으로 변환되었다. 하소온도를 $1,400^{\circ}C$로, 승온속도를 $50^{\circ}C$/min 로 증가시키고, 유지시간을 0.5 시간으로 감소시켜 급속 하소시킴으로써 인접입자의 소결을 상당히 감소시킬 수 있었다. $AlCl_3$의 가수분해 과정에서 소량의 $SiCl_4$ 또는 TMCTS(2,4,6,8-tetramethylcylosiloxane) 첨가에 의해 인접입자의 소결 방지 효과가 나타났으나, ${\alpha}$ 결정 이외에 ${\gamma}$ 결정, mullite 결정 등이 함께 생성되었다. 하소과정에서 $AlF_3$를 첨가한 결과 육각형 디스크 형상의 ${\alpha}$ 알루미나 입자가 생성되었다.