• Title/Summary/Keyword: Particle Size Reduction

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Effect of Heat-Treatment on the Crystallization of B Powder and Critical Current Density Property of MgB2 Superconductor (보론 분말의 결정화에 대한 열처리 영향과 MgB2 초전도체의 임계전류밀도 특성)

  • You, Byung Youn;Kim, Chan-Joong;Park, Soon-Dong;Jun, Byung-Hyuk
    • Korean Journal of Materials Research
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    • v.24 no.9
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    • pp.465-468
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    • 2014
  • The crystallization effects of boron (B) powder on the phase, full width at half maximum (FWHM) values, and critical properties were investigated for in-situ reacted $MgB_2$ bulk superconductors. The semi-crystalline B powder was heat-treated at different temperatures of 1000, 1300 and $1500^{\circ}C$ for 5 hours in an Ar atmosphere. Then, using as-received and heat-treated B powders, the $MgB_2$ samples were prepared at $600^{\circ}C$ for 40 hours in an Ar atmosphere. As the heat-treatment temperature of the B powder increased, both the particle size of the B powder and crystalline phase increased. In the case of $MgB_2$ samples using B powders heat-treated at above $1300^{\circ}C$, unreacted magnesium (Mg) and B remained due to the improved crystallinity of the B powder. As the heat-treatment temperature of B powder increased, the critical current density of $MgB_2$ decreased continuously due to the reduction of grain boundary density and superconducting volume caused by unreacted Mg and B.

Investigation of Nanometals (Ni and Sn) in Platinum-Based Ternary Electrocatalysts for Ethanol Electro-oxidation in Membraneless Fuel Cells

  • Ponmani, K.;Kiruthika, S.;Muthukumaran, B.
    • Journal of Electrochemical Science and Technology
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    • v.6 no.3
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    • pp.95-105
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    • 2015
  • In the present work, Carbon supported Pt100, Pt80Sn20, Pt80Ni20 and Pt80Sn10Ni10 electrocatalysts with different atomic ratios were prepared by ethylene glycol-reduction method to study the electro-oxidation of ethanol in membraneless fuel cell. The electrocatalysts were characterized in terms of structure, morphology and composition by using XRD, TEM and EDX techniques. Transmission electron microscopy measurements revealed a decrease in the mean particle size of the catalysts for the ternary compositions. The electrocatalytic activities of Pt100/C, Pt80Sn20/C, Pt80Ni20/C and Pt80Sn10Ni10/C catalysts for ethanol oxidation in an acid medium were investigated by cyclic voltammetry (CV) and chronoamperometry (CA). The electrochemical results showed that addition of Ni to Pt/C and Pt-Sn/C catalysts significantly shifted the onset of ethanol and CO oxidations toward lower potentials. The single membraneless ethanol fuel cell performances of the Pt80Sn10Ni10/C, Pt80Sn20/C and Pt80Ni20/C anode catalysts were evaluated at room temperature. Among the catalysts investigated, the power density obtained for Pt80Sn10Ni10/C (37.77 mW/cm2 ) catalyst was higher than that of Pt80Sn20/C (22.89 mW/cm2 ) and Pt80Ni20/C (16.77 mW/ cm2 ), using 1.0 M ethanol + 0.5 M H2SO4 as anode feed and 0.1 M sodium percarbonate + 0.5 M H2SO4 as cathode feed.

Combustion Characteristics and Activation Energy From Thermogravimetric Analysis of Bituminous and Anthracite Coal (TGA에 의한 유.무연탄의 연소특성과 활성화에너지 비교)

  • 김성철;최병선;이현동;홍성선
    • Journal of Energy Engineering
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    • v.5 no.2
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    • pp.170-175
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    • 1996
  • This study is to determined the activation energy from TGA experimental data for the bituminous and anthracite coals of three kinds which are being used in the domestic coal-fired power plants. TGA experimental data indicate that the weight loss temperature of bituminous coal is 200$^{\circ}C$ higher than that of anthracite coal. Activation energy of bituminous coal is in the range of 14∼20 Kcal/mole compared with 37∼55 Kcal/mole of anthracite coal. A reduction of particle size of coals results in the decrease of activation energy and activation energy has a good correlation with the weight loss percent of coal in the TGA experiment. Addition of CaCO$_3$ on anthracite coal caused to decrease the activation energy of 1∼23 Kcal/mole while activation energy of bituminous coal do not change significantly.

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Effects of Different Precursors on the Surface Mn Species Over $MnO_x/TiO_2$ for Low-temperature SCR of NOx with $NH_3$

  • Kim, Jang-Hoon;Yoon, Sang-Hyun;Lee, Hee-Soo
    • Proceedings of the Materials Research Society of Korea Conference
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    • 2011.10a
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    • pp.29.1-29.1
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    • 2011
  • The selective catalytic reduction (SCR) of $MnO_x$ with $NH_3$ is an effective method for the removal of $MnO_x$ from stationary system. The typical catalyst for this method is $V_2O_5-WO_3(MoO_3)/TiO_2$, caused by the high activity and stability. However, This catalyst is active within $300{\sim}400^{\circ}C$ and occurs the pore plugging from the deposition of ammonium sulfate salts on the catalysts surface. It needs to locate the SCR unit after the desulfurizer and electrostatic precipitator without reheating of the flue gas as well as deposition of dust on the catalyst. The manganese oxides supported on titania catalysts have attracted interest because of its high SCR activity at low temperature. The catalytic activity of $MnO_x/TiO_2$ SCR catalyst with different manganese precursors have investigated for low-temperature SCR in terms of structural, morphological, and physico-chemical analyses. The $MnO_x/TiO_2$ were prepared from three different precursors such as manganese nitrate, manganese acetate (II), and manganese acetate (III) by the sol-gel method and then it calcinated at $500^{\circ}C$ for 2 hr. The structural analysis was carried out to identify the phase transition and the change intensity of catalytic activity by various manganese precursors was analyzed by FT-IR and Raman spectroscopy. These different precursors also led to various surface Mn concentrations indicated by SEM. The Mn acetate (III) tends to be more suppressive the crystalline phase (rutile), and it has not only smaller particle size, but also better distributed than the others. It was confirmed that the catalytic activity of MA (III)-$MnO_x/TiO_2$ was the highest among them.

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Nano-sized Drug Carriers and Key Factors for Lymphatic Delivery

  • Choi, Ji-Hoon;Lee, Yong-Bok
    • Journal of Pharmaceutical Investigation
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    • v.40 no.spc
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    • pp.75-82
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    • 2010
  • Specific diseases like cancer and acquired immune deficiency syndrome (AIDS) occur at various organs including lymphatics and spread through lymphatic system. Thus, if therapeutic agents for such diseases are more distributed or targeted to lymphatic system, we can obtain several advantages like reduction of systemic side effect and increase of efficacy. For these reasons, much interest has been focused on the nature of lymphatics and a lot of studies for lymphatic delivery of drugs have been carried out. Because lymphatics consist of single layer endothelium and have high permeability compared with blood capillaries, especially, the studies using nano-sized carriers have been performed. Polymeric nano-particle, liposome, and lipid-based vehicle have been adopted for lymphatic delivery as carriers. According to the administration route and the kind of carrier, the extent of lymphatic delivery efficiency of nano-sized carriers has been changed and influenced by several factors such as size, charge, hydrophobicity and surface feature of carrier. In this review, we summarized the key factors which affect lymphatic uptake and the major features of carriers for achieving the lymphatic delivery. Lymphatic delivery of drug using nano-sized carriers has many fold improved ability of lymphatic delivery compared with that of conventional dosage forms, but it has not shown whole lymph selectivity yet. Even though nano-sized carriers still have the potential and worth to study as lymphatic drug delivery technology as before, full understanding of delivery mechanism and influencing factors, and setting of pharmacokinetic model are required for more ideal lymphatic delivery of drug.

Hydrogen Production from Ethanol Steam Reforming over SnO2-K2O/Zeolite Y Catalyst

  • Lee, Jun-Sung;Kim, Ji-Eun;Kang, Mi-Sook
    • Bulletin of the Korean Chemical Society
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    • v.32 no.6
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    • pp.1912-1920
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    • 2011
  • The $SnO_2$ with a particle size of about 300 nm instead of Ni is used in this study to overcome rapid catalytic deactivation by the formation of a $NiAl_2O_4$ spinal structure on the conventional Ni/${\gamma}$-$Al_2O_3$ catalyst and simultaneously impregnated the catalyst with potassium (K). The $SnO_2-K_2O$ impregnated Zeolite Y catalyst ($SnO_2-K_2O$/ZY) exhibited significantly higher ethanol reforming reactivity that that achieved with $SnO_2$ 100 and $SnO_2$ 30 wt %/ZY catalysts. The main products from ethanol steam reforming (ESR) over the $SnO_2$-$K_2O$/ZY catalyst were $H_2$, $CO_2$, and $CH_4$, with no evidence of any CO molecule formation. The $H_2$ production and ethanol conversion were maximized at 89% and 100%, respectively, over $SnO_2$ 30 wt %-$K_2O$ 3.0 wt %/ZY at 600 $^{\circ}C$ for 1 h at a $CH_3CH_2OH:H_2O$ ratio of 1:1 and a gas hourly space velocity (GHSV) of 12,700 $h^{-1}$. No catalytic deactivation occurred for up to 73 h. This result is attributable to the easier and weaker of reduction of Sn components and acidities over $SnO_2-K_2O$/ZY catalyst, respectively, than those of Ni/${\gamma}$-$Al_2O_3$ catalysts.

Behavior of Graphite and Formation of Intermetallic Compound Layer in Hot Dip Aluminizing of Cast Iron (주철 - 알루미늄 합금의 Hot Dip Aluminizing시 흑연 및 금속간화합물 층의 형성 거동)

  • Han, Kwang-Sic;Kang, Yong-Joo;Kang, Mun-Seok;Kang, Sung-Min;Kim, Jin-Su;Son, Kwang-Suk;Kim, Dong-Gyu
    • Journal of Korea Foundry Society
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    • v.31 no.2
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    • pp.66-70
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    • 2011
  • Hot dip aluminizing (HDA) is widely used in industry for improving corrosion resistance of material. The formation of intermetallic compound layers during the contact between dissimilar materials at high temperature is common phenomenon. Generally, intermetallic compound layers of $Fe_2Al_5$ and $FeAl_3$ are formed at the Al alloy and Fe substrate interface. In case of cast iron, high contact angle of graphite existed in the matrix inhibits the formation of intermetallic compound layer, which carry with it the disadvantage of a reduced reaction area and mechanical properties. In present work, the process for the removal of graphite existed on the surface of specimen has been investigated. And also HDA was proceeded at $800^{\circ}C$ for 3 minutes in aluminum alloy melt. The efficiency of graphite removal was increased with the reduction of particle size in sanding process. Graphite appears to be present both in the region of melting followed by re-solidification and in the intermetallic compound layer, which could be attributed to the fact that the surface of cast iron is melted down by the formation of low melting point phase with the diffusion of Al and Si to the cast iron. Intermetallic compound layer consisted of $Fe(Al,Si)_3$ and $Fe_2Al_5Si$, the layer formed at cast iron side contained lower amount of Si.

Gas Sensing Characteristics and Preparation of SnO2 Nano Powders (SnO2 나노 분말의 합성 및 가스 감응 특성)

  • Lee, Ji-Young;Yu, Yoon-Sic;Yu, Il
    • Journal of the Korean Institute of Electrical and Electronic Material Engineers
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    • v.24 no.7
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    • pp.589-593
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    • 2011
  • [ $SnO_2$ ]nano powders were prepared by solution reduction method using tin chloride($SnCl_2{\cdot}2H_2O$), hydrazine($N_2H_4$) and NaOH. The $SnO_2$ thick films for gas sensors were fabricated by screen printing method on alumina substrates and annealed at $300^{\circ}C$ in air, respectively. XRD patterns of the $SnO_2$ nano powders showed the tetragonal structure with (110) dominant orientation. The particle size of $SnO_2$ nano powders at the ratio of $SnCl_2:N_2H_4$+NaOH= 1:6 was about 60 nm. The sensing characteristics were investigated by measuring the electrical resistance of each sensor in a test box. Sensitivity of $SnO_2$ gas sensor to 5 ppm $CH_4$gas and 5 ppm $CH_3CH_2CH_3$ gas was investigated for various $SnCl_2:N_2H_4$+NaOH proportion. The highest sensitivity to $CH_4$ gas and $CH_3CH_2CH_3$ gas of $SnO_2$ sensors was observed at the $SnCl_2:N_2H_4$+NaOH= 1:8 and $SnCl_2:N_2H_4$+NaOH= 1:6, respectively. Response and recovery times of $SnO_2$ gas sensors prepared by $SnCl_2:N_2H_4$+NaOH= 1:6 was about 40 s and 30 s, respectively.

Basic Study on the in-situ Biogenic Methane Generation from Low Grade Coal Bed (저품위 석탄의 원지반에서의 생물학적 메탄가스 생산에 관한 기초연구)

  • Wang, Fei;Jeon, Ji-Young;Lim, Hak-Sang;Yoon, Seok-Pyo
    • Journal of the Korea Organic Resources Recycling Association
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    • v.23 no.4
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    • pp.11-20
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    • 2015
  • In the present work, a basic study on the in-situ biogenic methane generation from low grade coal bed was conducted. Lignite from Indonesia was used as a sample feedstock. A series of BMP (Biochemical Methane Potential) tests were carried out under the different experimental conditions. Although nutrients and anaerobic digester sludge were added to the coal, the produced amount of methane was limited. Both temperature control and particle size reduction showed little effect on the increase of methane potential. When rice straw was added to lignite as an external carbon source, methane yield of 94.4~110.4 mL/g VS was obtained after 60 days of BMP test. The calorific value of lignite after BMP test decreased (4.5~12.1 %) as increasing the content of rice straw (12.5~50 wt % of lignite), implying that anaerobic digestion of rice straw led to partial degradation of lignite. Therefore, rice straw could be used as an external carbon source for the start-up of in-situ biogas generation from low grade coal bed.

Electrical Properties of Supercapacitor Based on Dispersion Controlled Graphene Oxide According to the Change of Solution State by Washing Process (Washing을 통한 상분리 변화에 따른 그래핀 산화물의 분산도 조절 및 슈퍼커패시터의 특성에 관한 연구)

  • Sul, Ji-Hwan;You, In-kyu;Kang, Seok Hun;Kim, Bit-Na;Kim, In Gyoo
    • Journal of the Korean Institute of Electrical and Electronic Material Engineers
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    • v.31 no.2
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    • pp.102-106
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    • 2018
  • Recently, there has been an increasing interest in the use of graphene as electrode materials for supercapacitors. In this regard, graphene oxide (GO) films were prepared using GO slurry obtained by dispersing GO powder in deionized (DI) water. The degree of dispersion of GO powder in DI water depends on the concentration of GO slurry, pH, impurity content, GO particle size, types of functional groups contained in GO, and manufacturing method of GO powder. In this study, the dispersivity of the GO powder was improved by adjusting the pH using only DI water (without additives), and a uniform GO film was obtained. The GO film was reduced by exposure to xenon intense pulsed light for a few milliseconds, and the reduced GO film was used as electrodes of a supercapacitor. The supercapacitor was characterized using cyclic voltammetry (CV), charge-discharge cycle, and electrochemical impedance spectroscopy measurements, and the specific capacitance of the supercapacitor was found to be ~140 F/g from the CV data.