• Title, Summary, Keyword: Non-stoichiometric

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A Study on Nitridation and Oxidation Reaction of Titanium Powder (금속티타늄분말의 질화반응과 산화반응에 관한 연구)

  • Lee, Young-Ki;Sohn, Yong-Un;Cho, Young-Soo;Kim, Yong Seog;Kim, Suk-Yoon
    • Journal of the Korean Society for Heat Treatment
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    • v.8 no.2
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    • pp.137-148
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    • 1995
  • The nitridation kinetics of titanium powder were studied by isothermal and non-isothermal (dynamic) methods in high purity nitrogen under I atm pressure. For the comparison with nitridation, the oxidation kinetics of titanium powder were also studied in dry oxygen at I atm pressure. An automatic recording electrobalance was used to measure the weight gain as a function of time and temperature. For the reaction with nitrogen, the nitride was formed at over $700^{\circ}C$. The reaction with nitrogen followed the parabolic rate law, and the activation energy was calculated to be 31 kcal/mol in the isothermal method (above $900^{\circ}C$). The non-stoichiometric TiNx has been synthesized by the nitridation at a proper temperature and time, followed by the homogenizing treatment above $1100^{\circ}C$. In comparison with the stoichiometric $TiN_{1.0}$ and the non-stoichiometric TiNx ($TiN_{0.5}$ and $TiN_{0.65}$), the hot oxidation characteristics of the former is superior to that of the latter. However, both non-stoichiometric nitrides make little difference in the hot oxidation characteristics.

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Non-stoichiometric AlOx Films Prepared by Chemical Vapor Deposition Using Dimethylaluminum Isopropoxide as Single Precursor and Their Non-volatile Memory Characteristics

  • Lee, Sun-Sook;Lee, Eun-Seok;Kim, Seok-Hwan;Lee, Byung-Kook;Jeong, Seok-Jong;Hwang, Jin-Ha;Kim, Chang-Gyoun;Chung, Taek-Mo;An, Ki-Seok
    • Bulletin of the Korean Chemical Society
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    • v.33 no.7
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    • pp.2207-2212
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    • 2012
  • Dimethylaluminum isopropoxide (DMAI, $(CH_3)_2AlO^iPr$) as a single precursor, which contains one aluminum and one oxygen atom, has been adopted to deposit non-stoichiometric aluminum oxide ($AlO_x$) films by low pressure metal organic chemical vapor deposition without an additional oxygen source. The atomic concentration of Al and O in the deposited $AlO_x$ film was measured to be Al:O = ~1:1.1 and any serious interfacial oxide layer between the film and Si substrate was not observed. Gaseous by-products monitored by quadruple mass spectrometry show that ${\beta}$-hydrogen elimination mechanism is mainly contributed to the $AlO_x$ CVD process of DMAI precursor. The current-voltage characteristics of the $AlO_x$ film in Au/$AlO_x$/Ir metalinsulator-metal (MIM) capacitor structure show high ON/OFF ratio larger than ${\sim}10^6$ with SET and RESET voltages of 2.7 and 0.8 V, respectively. Impedance spectra indicate that the switching and memory phenomena are based on the bulk-based origins, presumably the formation and rupture of filaments.

Kinetics of Methyl Green Fading in the Presence of TX-100, DTAB and SDS

  • Samiey, Babak;Dalvand, Zeinab
    • Bulletin of the Korean Chemical Society
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    • v.34 no.4
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    • pp.1145-1152
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    • 2013
  • The rate constant of alkaline fading of methyl green ($ME^{2+}$) was measured in the presence of non ionic (TX-100), cationic (DTAB) and anionic (SDS) surfactants. $ME^{2+}$ hydrolyses and fades in neutral water and in this work we search the effects of surfactants on its fading rate. The rate of reaction showed remarkable dependence on the electrical charge of the used surfactants. It was observed that the reaction rate constant decreased in the presence of DTAB and SDS and increased in the presence of TX-100. Binding constants of $ME^{2+}$ to TX-100, DTAB and SDS and the related thermodynamic parameters were obtained by classical (or stoichiometric) model. The results show that binding of $ME^{2+}$ to TX-100 and DTAB are two-region and that of SDS is three-region. Also, the binding constants of $ME^{2+}$ to surfactant molecules in DTAB/TX-100 and SDS/TX-100 mixed solutions and their stoichiometric ratios were obtained.

Exsolution of $Bi_4Ge_3O_12$ in $Bi_12GeO_20$ Crystals Grown by Pulling Method (인상 육성한 $Bi_12GeO_20$ 결정내의 $Bi_4Ge_3O_12$석출상)

  • 이태근;정수진
    • Journal of the Korean Ceramic Society
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    • v.28 no.12
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    • pp.981-988
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    • 1991
  • Various crystal defects such as voids, inclusions dislocations, stacking faults and precipitates were observed in the Czochralski-grown Bi12GeO20 crystals. Particularly, precipitates were found in the whole crystals. The phase of these precipitates was identified as Bi4Ge3O12 by EPMA and transmission electron microscopy. The precipitates were produced by pulling rapidly from a non-stoichiometric charge. During the pulling of Bi12GeO20 crystals, the melt composition of stoichiometric charge was changed Bi-deficent with gradual volatilization of Bi2O3. Precipition of the second phase may have been affected by an abrube thermal stress. By adding excess Bi2O3 into the stoichiometric batch, the precipitation of Bi4Ge3O12 was suppressed. At a pulling speed of 2 mm/hr, clear and precipitate from crystals of Bi12GeO20 were grown from the melt of the Bi2O3 excess charge.

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Conversion Process of Amorphous Si-Al-C-O Fiber into Nearly Stoichiometric SiC Polycrystalline Fiber

  • Usukawa, Ryutaro;Oda, Hiroshi;Ishikawa, Toshihiro
    • Journal of the Korean Ceramic Society
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    • v.53 no.6
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    • pp.610-614
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    • 2016
  • Tyranno SA (SiC-polycrystalline fiber, Ube Industries Ltd.) shows excellent heat-resistance up to $2000^{\circ}C$ with relatively high mechanical strength. This fiber is produced by the conversion process from a raw material (amorphous Si-Al-C-O fiber) into SiC-polycrystalline fiber at very high temperatures over $1500^{\circ}C$ in argon. In this conversion process, the degradation reaction of the amorphous Si-Al-C-O fiber accompanied by a release of CO gas for obtaining a stoichiometric composition and the subsequent sintering of the degraded fiber proceed. Furthermore, vaporization of gaseous SiO, phase transformation and active diffusion of the components of the Si-Al-C-O fiber competitively occur. Of these changes, vaporization of the gaseous SiO during the conversion process results in an abnormal SiC-grain growth and also leads to the non-stoichiometric composition. However, using a modified Si-Al-C-O fiber with an oxygen-rich surface, vaporization of the gaseous SiO was effectively prevented, and then consequently a nearly stoichiometric SiC composition could be obtained.

ION BEAM AND ITS APPLICATIONS

  • Koh, S.K.;Choi, S.C.;Kim, K.H.;Cho, J.S.;Choi, W.K.;Yoon, Y.S.;Jung, H.J.
    • Journal of the Korean Vacuum Society
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    • v.6 no.S1
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    • pp.110-114
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    • 1997
  • Development of metal ion source growth of high quality Cu metal film formation of non-stoichiometric $SnO_2$ films of Si(100), and modification fo polymer surface by low enregy ion beam have been carried out at KIST Ion Beam Lab. A new metal ion source with high ion beam flux has been developed by a hybrid ion beam (HIB) deposition and non-stoichiometric $SnO_2$ films are controlled by supplying energy. The ion assisted reaction (IAR) in which keV ion beam is irradiated in reactive gas environment has been deveolped for modifying the polymers and enhancing adhesion to other materials and advantages of the IAR have been reviewed.

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The Origin of the Metal-insulator Transitions in Non-stoichiometric TlCu3-xS2 and α-BaCu2-xS2

  • Jung, Dong-woon;Choi, Hyun-Guk;Kim, Han-jin
    • Bulletin of the Korean Chemical Society
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    • v.27 no.3
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    • pp.363-367
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    • 2006
  • The structure-property relations of ternary copper chalcogenides, $TlCu_{3-x}S_2$ and $\alpha-BaCu_{2-x}S_2$ are examined. The density of states, band dispersions, and Fermi surfaces of these compounds are investigated to verify the reason of the metal-insulator transitions by extended Huckel tight-binding band calculations. The origin of the metalinsulator transitions of non-stoichiometric $TlCu_{3-x}S_2$ and $\alpha-BaCu_{2-x}S_2$ is thought to be the electronic instability induced by their Fermi surface nesting.

The electrode characteristics of non-stoichiometric Zr-based Laves phase alloys (Non-Stoichiometric Zr-Based 라베스상 수소저장합금의 방전특성)

  • Kim, Dong-Myung;Jung, Jai-Han;Lee, Han-Ho;Lee, Jai-Young
    • Transactions of the Korean hydrogen and new energy society
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    • v.7 no.1
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    • pp.11-18
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    • 1996
  • The Laves phase alloy hydrides have some promising properties as electrode materials in reversible metal hydride batteries. In this work, the hydrogen storage performance, crystallographic parameters, surface morphology, surface area and electrochemical characteristics of the non-stoichiometric $ZrMn_{0.3}V_{0.7}Ni_{1.4+{\alpha}}$, $ZrMn_{0.5}V_{0.5}Ni_{1.4+{\alpha}}$($\alpha$ =0.0, 0.2, 0.4, 0.6) alloys were examined. These as-cast alloys were found to have mainly a cubic C15-type Laves phase structure by X -ray diffraction analysis. The equilibrium pressure of the alloy were increased as $\alpha$ increased in both two types alloy. In case of $ZrMn_{0.5}V_{0.5}Ni_{1.4+{\alpha}}$ alloys, discharge efficiency and the rate capability of the alloy were decreased as $\alpha$ increased but, these values were increased in case of $ZrMn_{0.3}V_{0.7}Ni_{1.4+{\alpha}}$ alloys. The differences of these electrode properties observed were dependent on the reaction surface area and the catalytic activity of unit area of the each electrode.

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Piezoelectric and Dielectric Properties of Non-stochiometric(K0.5Na0.5)0.97(Nb0.96-xTaxSb0.04)O3 Ceramics (비화학양론적인 (K0.5Na0.5)0.97(Nb0.96-xTaxSb0.04)O3 세라믹스의 유전 및 압전특성)

  • Sin, Sang-Hoon;Noh, Jung-Rae;Yoo, Ju-Hyun
    • Journal of the Korean Institute of Electrical and Electronic Material Engineers
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    • v.25 no.8
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    • pp.611-615
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    • 2012
  • In this study non-stoichiometric $(K_{0.5}Na_{0.5})_{0.97}(Nb_{0.96-x}Ta_xSb_{0.04})O_3$ ceramics were prepared by the conventional soild-state teaction method. The effect of Ta-substitution on the dielectric and piezoelectric properties were investigated. X-ray diffraction analysis of all the specimens less than x= 15 mol% indicated orthorhombic phase. Thereafter, the specimens showed orthorhombic phase near to pseudo-cubic. Sinterablity of all the specimens was improved due to secondary products such as KCT and KCN. The ceramics with x= 5 mol% showed the optimum velues of pizoelectric constant($d_{33}$)= 150 pC/N, electromechanical coupling factor (kp)= 0.45, electromechanical quality factor (Qm)= 418.9 and dielectric constant(${\varepsilon}_r$)= 567. Accordingly, These results indicate that the composition ceramics is a promising candidate for lead-free material.