• Title/Summary/Keyword: Solid state reaction

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Electrochemical Properties of Spinel LiMn2O4 Prepared Through Different Synthesis Routes (스피넬형 양극활물질 LiMn2O4의 합성방법에 따른 전기화학적 특성 비교)

  • Lee, Ki-Soo;Bang, Hyun-Joo;Sun, Yang-Kook
    • Journal of the Korean Electrochemical Society
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    • v.10 no.1
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    • pp.48-51
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    • 2007
  • In order to investigate the effects of particle size and specific surface area(BET area) of spinel powder, $LiMn_2O_4$ were synthesized using metal oxide precursor by co-precipitation method(CoP) and solid state reaction (SSR) .X-ray diffraction(XRD) patterns revealed that the both prepared powder has a well developed spinel structure with Fd3m space group. The $LiMn_2O_4$ prepared by co-precipitation showed spherical morphology with narrow size distribution. However, the $LiMn_2O_4$ prepared by solid state reaction showed relatively smaller particles with irregular shape. The measured BET areas of the powers are $0.8m^2g^{-1}$ (CoP) and $3.6m^2g^{-1}$(SSR). The electrochemical performance of the Prepared $LiMn_2O_4$ powders was evaluated using coin type cells(CR2032) at elevated temperature ($55^{\circ}C$). The $LiMn_2O_4$ prepared by co-precipitation showed the better cycling performance(82.3%capacity retention at $50^{th}$ cycle) than that of the $LiMn_2O_4$(68.3%) prepared by solid state reaction at elevated temperature.

In-situ Fourier Transform Infrared Spectroscopic Study during Thermolysis of Trimethylaluminum and its Adduct (Trimethylaluminum (TMA), $NH_3$ 및 TMA :$NH_3$Adduct의 열분해 반응에 대한 in-situ FTIR 분광학적 연구)

  • Hyang Sook Kim;Seong Han Kim;Jin Soo Hwang;Joong Gill Choi;Paul Joe Chong
    • Journal of the Korean Chemical Society
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    • v.37 no.12
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    • pp.995-1002
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    • 1993
  • The thermal decomposition of trimethylaluminum (TMA) with ammonia has been investigated by in-situ Fourier transform infrared spectroscopy. The spectroscopic reaction cell, which permits heating interna lly up to 1100$^{\circ}C$, consists of stainless-steel hexagonal-port chamber containing two NaCl windows installed in parallel. In this work, the stoichiometric reaction between TMA and $NH_3$ is found to be completed immediately after mixing. FTIR spectra observed in the range of temperature 25∼1100$^{\circ}C$ show that TMA and TMA : $NH_3$ adduct decompose into methane as a predominant product around 500$^{\circ}C$. The assignments of the IR bands due to the gaseous TMA, $NH_3$ and TMA : $NH_3$ adduct are attempted on the basis of the published data. Furthermore, the decomposition of TMA can be described as a first-order reaction. Kinetic data about the decompositon of TMA and TMA : $NH_3$adduct will also be discussed.

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Radical Addition Reaction of Phosphorous based Flame Retardant with End Groups of PET (1) - Reaction of Bisphenol A bis(diphenyl phosphate) - (PET 말단에 대한 인계난연제의 라디칼계 부가반응 (1) - 비스페놀에이비스다이페닐포스페이트의 반응 -)

  • Kim, Min-Kwan;Ghim, Han-Do
    • Textile Coloration and Finishing
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    • v.24 no.1
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    • pp.33-38
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    • 2012
  • In this study, to increase flame retardation of poly(ethylene terephthalate) (PET) in burning, bisphenol A bis(diphenyl phosphate) (BDP), a well known flame retardant containing phosphorous, was reacted on end groups of PET by radical pathway. End-capping mechanism of PET with BDP was suggested and confirmed by spectroscopic and thermal analysis. From 400 MHz $^{31}P$ solid state FT-NMR spectrum of end-capped PET (PET-BDP), phosphorus spectra peak in BDP was found at ca. -20 ppm. Furthermore, P-C bond stretching vibration peaks were found ca. $600cm^{-1}$ in FT-IR spectrums of PET-BDP. These results showed that BDP can be chemically added on end groups of PET by our method. Thermal characteristics of pure PET (pPET) and PET-BDP were measured and evaluated by TGA analysis. There was not significant changes in thermal characteristics of PET-BDP compared to that of pPET.

Interaction of Gas-phase Atomic Hydrogen with Chemisorbed Oxygen Atoms on a Silicon Surface

  • Lee, Sang-Kwon;Ree, Jong-Baik;Kim, Yoo-Hang;Shin, Hyung-Kyu
    • Bulletin of the Korean Chemical Society
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    • v.32 no.5
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    • pp.1527-1533
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    • 2011
  • The reaction of gas-phase atomic hydrogen with oxygen atoms chemisorbed on a silicon surface is studied by use of the classical trajectory approach. We have calculated the probability of the OH formation and energy deposit of the reaction exothermicity in the newly formed OH in the gas-surface reaction H(g) + O(ad)/Si${\rightarrow}$ OH(g) + Si. All reactive events occur in a single impact collision on a subpicosecond scale, following the Eley-Rideal mechanism. These events occur in a localized region around the adatom site on the surface. The reaction probability is dependent upon the gas temperature and shows the maximum near 1000 K, but it is essentially independent of the surface temperature. The reaction probability is also independent upon the initial excitation of the O-Si vibration. The reaction energy available for the product state is carried away by the desorbing OH in its translational and vibrational motions. When the initial excitation of the O-Si vibration increases, translational and vibrational energies of OH rise accordingly, while the energy shared by rotational motion varies only slightly. Flow of energy between the reaction zone and the solid has been incorporated in trajectory calculations, but the amount of energy propagated into the solid is only a few percent of the available energy released in the OH formation.

Preparation of Ultrafine Barium Titanate Powder by Slurry Spray Pyrolysis (슬러리 분무열분해에 의한 초미립 티탄산 바륨 분말 제조)

  • Lee, Jong-Ho;Hur, Kang-Heon;Lee, Jung-Soo
    • Journal of the Korean Ceramic Society
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    • v.46 no.2
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    • pp.137-145
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    • 2009
  • A remarkable improvement of the productivity in barium titanate by slurry spray pyrolysis process was realized by supplying solid source slurry into the rector. The produced barium titanate powders showed uniform powder properties, and reproducibility with higher tetragonality in the range of 80$\sim$200 nm, case by case. The secondary calcination experiments of the as-prepared powders by spray pyrolysis revealed that the powders as-prepared over 700$^{\circ}C$ showed perfectly different behavior with the lower temperature's ones and the solid state reaction’s case. The result was discussed in terms of the reaction mechanism based on the activation energy analysis.

Oxygen Evolution Reaction at Electrodes of Single Phase Ruthenium Oxides with Perovskite and Pyrochlore Structures$^{**}$

  • 최은옥;권영욱;모선일
    • Bulletin of the Korean Chemical Society
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    • v.18 no.9
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    • pp.972-976
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    • 1997
  • Single phase ruthenium oxides with perovskite (ATi1-xRuxO3 (A=Ca, Sr)) and pyrochlore structure (Bi2Ru2O7, Pb2Ru2O6.5) have been prepared reproducibly by solid state reaction methods and their electrocatalytic activities for oxygen evolution have been examined by Tafel plots. Tafel slopes vary from a low value of 42 mV/decade up to 222 mV/decade at room temperature. The high exchange current densities and high Tafel slopes compared with those obtained from the RuO2 DSA electrode at the crystalline single phase metal oxide electrodes suggest that they are better electrocatalysts at low overpotentials. A favorable change in the Tafel slope for the oxygen evolution reaction occurs as the ruthenium content increases. Substitution of Ti for Ru in the perovskite solid solutions enhanced their chemical stability by losing marginal electrochemical activity.

Reaction-Bonded Al2O3 Ceramics Using Oxidation of Al Alloy Powder

  • Lee, Hyun-Kwuon
    • Korean Journal of Materials Research
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    • v.24 no.5
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    • pp.236-242
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    • 2014
  • Fabrication of reaction-bonded $Al_2O_3$ (RBAO) ceramics using Al-Zn-Mg alloy powder was studied in order to improve traditional RBAO ceramic processing using Al powder. The influence on reaction-bonding and microstructure, as well as on physical and mechanical properties, of the particulate characteristics of the $Al_2O_3$-Al alloy powder mixtures after milling, was revealed. Variation of the particulate characteristics of this $Al_2O_3$-Al alloy powder mixture with milling time was reported previously. To start, the $Al_2O_3$-Al alloy powder mixture was milled, reaction-bonded, post-sintered, and characterized. During reaction-bonding of the $Al_2O_3$-Al alloy powder mixture compacts, oxidation of the Al alloy took place in two stages, that is, there was solid- and liquid-state oxidation of the Al alloy. The solid-state oxidation exhibited strong dependence on the density of surface defects on the Al-alloy particles formed during milling. Higher milling efficiency resulted in less participation of the Al alloy in reaction-bonding. This was because of its consumption by chemical reactions during milling, and subsequent powder handling, and could be rather harmful in the case of over-milling. In contrast to very little dependence of oxidation of the Al alloy on its particle size after milling, the relative density, microstructure, and flexural strength were strongly dependent on particle size after milling (i.e., on milling efficiency). The relative density and 4-point flexural strength of the RBAO ceramics in this study were ~98% and ~365 MPa, respectively, after post-sintering at $1,600^{\circ}C$.

A Review on the Wet Chemical Synthesis of Sulfide Solid Electrolytes for All-Solid-State Li Batteries (전고체전지용 황화물 고체전해질 습식 합성기술 동향)

  • Ha, Yoon-Cheol
    • Journal of the Korean Electrochemical Society
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    • v.25 no.3
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    • pp.95-104
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    • 2022
  • The development of non-flammable all-solid-state batteries (ASSLBs) has become a hot topic due to the known drawbacks of commercial lithium-ion batteries. As the possibility of applying sulfide solid electrolytes (SSEs) for electric vehicle batteries increases, efforts for the low-cost mass-production are actively underway. Until now, most studies have used high-energy mechanical milling, which is easy to control composition and impurities and can reduce the process time. Through this, various SSEs that exceed the Li+ conductivity of liquid electrolytes have been reported, and expectations for the realization of ASSLBs are growing. However, the high-energy mechanical milling method has disadvantages in obtaining the same physical properties when mass-produced, and in controlling the particle size or shape, so that physical properties deteriorate during the full process. On the other hand, wet chemical synthesis technology, which has advantages in mass production and low price, is still in the initial exploration stage. In this technology, SSEs are mainly manufactured through producing a particle-type, solution-type, or mixed-type precursor, but a clear understanding of the reaction mechanism hasn't been made yet. In this review, wet chemical synthesis technologies for SSEs are summarized regarding the reaction mechanism between the raw materials in the solvent.

Synthesis and Characterisation of Mixed Conducting Perovskite Type Oxide and Its Electrochemical Application to Electrode Material for Solid Oxide Fuel Cell

  • Kim, Yu-Mi;Pyun, Su-Il;Lee, Gyoung-Ja;Kim, Ju-Sik
    • Journal of the Korean Electrochemical Society
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    • v.10 no.2
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    • pp.116-125
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    • 2007
  • This article is concerned with synthesis, characterisation and electrochemical application of the mixed conducting perovskite type oxide to electrode materials for solid oxide fuel cell. First, this review provides a comprehensive survey of the various synthetic methods such as solid state reaction, Pechini, glycine nitrate process and sol-gel methods for the preparation of perovskite type oxide powders. Subsequently, the electrical and microstructural properties of the mixed conducting oxides were discussed in detail. Finally, as electrochemical applications of the mixed conducting perovskite type oxides to electrode materials for solid oxide fuel cell, fundamentals of theoretical ac-impedance model for porous mixed conducting electrodes were introduced. Furthermore, the ac-impedance behaviour of porous and dense mixed conducting electrodes prepared by various synthetic methods was discussed.

Analysis for Steady-State and Transient Combustion Characteristic of Solid Propellant Rocket Engine (고체 추진제 로켓엔진의 정상 및 비정상 연소특성 해석)

  • 김후중;김용모;윤명원
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • 2003.05a
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    • pp.233-239
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    • 2003
  • The present study has numerically investigated the combustion processes in the solid propellant rocket engine. The two step global reaction model for condensed phase and five step global reaction mechanism for gas phase are adopted to predict the detailed flame structure near double-base solid propellant surface. The turbulence-chemistry interaction is represented by the PaSR(Partially Stirred Reactor) model. To reduce the uncertainties for convective heat transfer near solid fuel surface having strong blowing effect, the Low Reynolds number k-$\varepsilon$ turbulent model is employed. Based on numerical results, the detailed discussion has been made for the turbulent combustion processes and transient behavior of pressure and temperature fields in the solid propellant rocket engine.

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