The Experts below are selected from a list of 189 Experts worldwide ranked by ideXlab platform
Harumi Yokokawa - One of the best experts on this subject based on the ideXlab platform.
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Generalized Ellingham Diagrams for utilization in solid oxide fuel cells
Journal of Mining and Metallurgy Section B, 2020Co-Authors: Haruo Kishimoto, Katsuhiko Yamaji, Manuel E. Brito, Teruhisa Horita, Harumi YokokawaAbstract:Generalized Ellingham Diagram for the P-O-H and the Ni-P-OH systems have been constructed to investigate thermodynamically the chemical stability of nickel anode against the gaseous impurities containing phosphorous compounds. In the same way as the original Ellingham Diagram, the oxygen potential is used as the vertical axis, while the temperature is adopted as horizontal axis. For the P-O-H system which contains many gaseous species, the dominant areas of gaseous species are displayed with a parameter of their partial pressure in an analogous way to the aqueous species in the Pourbaix Diagram. The multicomponent Ellingham Diagram for the Ni-P-O-H system was constructed in a similar manner to the multicomponent Pourbaix Diagram. The obtained Diagrams have been discussed to examine the reactivity of nickel anodes with phosphorus compounds in SOFCs in terms of operational variables such as temperature, oxygen potential, overpotential under the anode polarization and so on.
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sulfur poisoning on sofc ni anodes thermodynamic analyses within local equilibrium anode reaction model
Journal of The Electrochemical Society, 2010Co-Authors: Haruo Kishimoto, Katsuhiko Yamaji, Manuel E. Brito, Teruhisa Horita, Harumi Yokokawa, Yueping XiongAbstract:Possible effects of sulfur on solid oxide fuel cell (SOFC) Ni anodes have been analyzed from the thermodynamic considerations of Ni―S―C―O―H systems by constructing the predominant area Diagrams as the Ellingham Diagram (oxygen potential vs temperature plot) with a parameter of partial pressure (10 ―4 or 10 ―6 atm) of sulfur-containing gaseous species such as H 2 S. Focus was made on the sulfur potential and its role on the sulfur adsorption on Ni, the sulfur dissolution into Ni, or the Ni sulfide formation, particularly on the eutectics formation. The important features of sulfur poisoning have been extracted and discussed as follows: (i) Under equilibrated conditions with 1-100 ppm contamination of H 2 S around 1073 K, Ni anodes are stable against sulfide formation up to a high utilization such as 90%. (ii) When the anode overpotential is strongly related to the change in oxygen potential in the vicinity of three-phase boundaries (TPBs), Ni can be sulfurized; in worse cases, Ni-S eutectic liquids can be formed. (iii) Several factors that can lead to serious damages are discussed in terms of diffusion of sulfur inside nickel, enhancement accumulation of sulfur at TPBs due to the electrochemical oxidation of H 2 S, and enrichment of sulfur in the lower temperature region in stacks.
Takuya Hashimoto - One of the best experts on this subject based on the ideXlab platform.
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Thermal analysis of structural phase transition behavior of Ln 2 Ni 1−x Cu x O 4+δ (Ln = Nd, Pr) under various oxygen partial pressures
Journal of Thermal Analysis and Calorimetry, 2018Co-Authors: Mamoru Sakai, Eiki Niwa, Chengkun Wang, Takashi Okiba, Haruki Soga, Takuya HashimotoAbstract:Structural phase transition behavior between orthorhombic and tetragonal in Ln2Ni1−xCuxO4+δ (Ln = Nd, Pr), which attracts interest as new cathode material for solid oxide fuel cells, has been investigated with thermal analysis under controlled oxygen partial pressures (P(O2)). For Nd2Ni1−xCuxO4+δ with 0.0 ≤ x ≤ 0.1, temperature, enthalpy change (ΔH) and change in excess oxygen content (Δδ) at the phase transition decreased with increasing Cu content. The phase transition temperature decreased with decreasing P(O2), whereas little variation was observed in ΔH and Δδ. For Nd2Ni1−xCuxO4+δ with x ≥ 0.15, crystal structure was tetragonal and no phase transition was detected below 750 °C. For Pr2Ni1−xCuxO4+δ with x = 0.0 and 0.1, phase transition was observed by DSC, showing similar dependence of phase transition temperature and ΔH on Cu content and P(O2) with that of Nd2Ni1−xCuxO4+δ. Δδ was not detected in TG curve of Pr2Ni0.9Cu0.1O4+δ, which could be attributed to too small Δδ. From Ellingham Diagram prepared using temperature and P(O2) at the phase transition, variation of standard enthalpy (ΔH°) and standard entropy (ΔS°) was evaluated. It was revealed that variation of phase transition temperature by Cu content and difference of the phase transition temperature between Nd2Ni1−xCuxO4+δ and Pr2Ni1−xCuxO4+δ showed correspondence with variation of ΔH°. Excess oxygen content, δ, in Nd2Ni1−xCuxO4+δ, evaluated with reduction in TG apparatus, decreased with increasing Cu content. It was suggested that some amount of δ was required for stabilization of orthorhombic phase and that low δ by Cu substitution stabilized the tetragonal structure of the specimens with x ≥ 0.15.
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Analysis of chemical reaction between Li4SiO4 and CO2 by thermogravimetry under various CO2 partial pressures—Clarification of CO2 partial pressure and temperature region of CO2 absorption or desorption
Materials Research Bulletin, 2017Co-Authors: Shingo Kaniwa, Eiki Niwa, Masatoshi Yoshino, Masatomo Yashima, Takuya HashimotoAbstract:Abstract Chemical reaction between CO2 and Li4SiO4 was investigated using thermogravimetry under various P(CO2). Under P(CO2) of 1.0 bar, weight increase originating from CO2 absorption reaction was observed from ∼500 °C and abrupt weight reduction due to CO2 desorption was detected at ∼700 °C. With decreasing P(CO2), the latter temperature decreased. Since fair agreement was observed between the latter temperatures and thermodynamically calculated equilibrium temperatures of Li4SiO4 + CO2 ↔ Li2CO3 + Li2SiO3, the latter temperatures could be regarded as approximate equilibrium. Dependence of the calculated equilibrium temperatures and approximate equilibrium temperatures on P(CO2) was represented with Ellingham Diagram, showing P(CO2) and temperature region of CO2 absorption or desorption. Approximate equilibrium temperature under P(CO2) of 1.0 bar agreed with the calculation, whereas deviation was observed under low P(CO2), resulted in larger apparent ΔS° and ΔH° than the calculated ones. Using specimen with smaller particle size, the deviation reduced due to enhancement of CO2 desorption kinetics.
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Analysis of thermal stability of LaNi_1−xFe_xO_3−δ (x = 0.0, 0.2, 0.4) by thermogravimetry and high-temperature X-ray diffraction under controlled oxygen partial pressures
Journal of Thermal Analysis and Calorimetry, 2016Co-Authors: Yuta Morishima, Eiki Niwa, Takuya HashimotoAbstract:Thermodynamic stability of LaNi_1−xFe_xO_3−δ ( x = 0.0, 0.2, 0.4), which is expected as new cathode material for solid oxide fuel cells, was investigated by thermogravimetry and high-temperature X-ray diffraction under controlled oxygen partial pressure, P (O_2). It was clarified that LaNiO_3− δ decomposed through La_4Ni_3O_10 to La_2NiO_4 with increasing temperature under P (O_2) of 10^−2 atm or more. The decomposition temperature decreased with reducing P (O_2). Under P (O_2) of 10^−3 atm, LaNiO_3− δ directly decomposed to La_2NiO_4. The decomposition of LaNi_1−xFe_xO_3−δ ( x = 0.2, 0.4) to La_4(Ni_1−xFe_x)_3O_10 was also observed, and Ellingham Diagram of the decomposition reaction was prepared. It was revealed that thermodynamically stable temperature and P (O_2) region expanded with increasing Fe content. Nonlinear decomposition boundary was observed in the Ellingham Diagram of LaNiO_3− δ and LaNi_0.8Fe_0.2O_3− δ whose origin can be suspected to the difference of δ at the decomposition on P (O_2). Linear decomposition boundary was observed for LaNi_0.6Fe_0.4O_3− δ , indicating variation of entropy, Δ S °, and enthalpy, Δ H °, at the decomposition were 151 J mol^−1 K^−1 and 240 kJ mol^−1, respectively.
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Analysis of thermal stability of LaNi1−xFexO3−δ (x = 0.0, 0.2, 0.4) by thermogravimetry and high-temperature X-ray diffraction under controlled oxygen partial pressures
Journal of Thermal Analysis and Calorimetry, 2015Co-Authors: Yuta Morishima, Eiki Niwa, Takuya HashimotoAbstract:Thermodynamic stability of LaNi1−xFexO3−δ (x = 0.0, 0.2, 0.4), which is expected as new cathode material for solid oxide fuel cells, was investigated by thermogravimetry and high-temperature X-ray diffraction under controlled oxygen partial pressure, P(O2). It was clarified that LaNiO3−δ decomposed through La4Ni3O10 to La2NiO4 with increasing temperature under P(O2) of 10−2 atm or more. The decomposition temperature decreased with reducing P(O2). Under P(O2) of 10−3 atm, LaNiO3−δ directly decomposed to La2NiO4. The decomposition of LaNi1−xFexO3−δ (x = 0.2, 0.4) to La4(Ni1−xFex)3O10 was also observed, and Ellingham Diagram of the decomposition reaction was prepared. It was revealed that thermodynamically stable temperature and P(O2) region expanded with increasing Fe content. Nonlinear decomposition boundary was observed in the Ellingham Diagram of LaNiO3−δ and LaNi0.8Fe0.2O3−δ whose origin can be suspected to the difference of δ at the decomposition on P(O2). Linear decomposition boundary was observed for LaNi0.6Fe0.4O3−δ , indicating variation of entropy, ΔS°, and enthalpy, ΔH°, at the decomposition were 151 J mol−1 K−1 and 240 kJ mol−1, respectively.
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Kinetics and Mechanism of Chemical Reaction of CO2 and Ba2Fe2O5 Under Various CO2 Partial Pressures
Journal of the American Ceramic Society, 2012Co-Authors: Fumito Fujishiro, Yuki Kojima, Takuya HashimotoAbstract:The reaction kinetics of the CO2 absorption by Ba2Fe2O5, which shows a reversible reaction with CO2 represented as Ba2Fe2O5 + CO2 ⇄ BaCO3 + BaFe2O4, was investigated by thermogravimetry under various CO2 partial pressures [P(CO2)s]. The calculated Ellingham Diagram of the reaction was found to show agreement with the variation in the equilibrium temperature of the reaction with P(CO2). The results of the morphology observation, specific surface area analysis, and TG measurement suggested that the CO2 absorption mechanism of Ba2Fe2O5 is described by a superficial reaction, a diffusion-controlled process, and a sintering reaction as the reaction proceeds. The kinetics of CO2 absorption for the diffusion-controlled process has been analyzed with the Jander function, showing that the activation enthalpy was about 1.6 × 102 kJ/mol.
Tai-hee Kang - One of the best experts on this subject based on the ideXlab platform.
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THE OPTIMAL FORMATION CONDITION OF CHROMIUM OXIDE THIN FILM ON STAINLESS-STEEL SURFACE
Surface Review and Letters, 2020Co-Authors: Sangwoon Moon, Sukmin Chung, Chongdo Park, Tai-hee KangAbstract:We investigated the various oxidation conditions of stainless-steel surface using synchrotron radiation photoemission spectroscopy. Stainless-steel samples are oxidized at 450–550°C in various oxygen partial pressures. Increasing the annealing temperature from 450°C to 550°C, the trivalent chromium concentration in the surface increased and iron oxides decreased. The PES spectra from stainless steels oxidized at 550°C show that there exists the critical oxygen partial pressure, [Formula: see text] Torr. Below this critical pressure, the oxide formed mainly consists of chromium oxide, while the oxide formed mainly consists of iron oxide above the critical pressure. The oxidation behavior is in good agreement with the Ellingham Diagram (a free-energy/temperature Diagram).
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THE OPTIMAL FORMATION CONDITION OF CHROMIUM OXIDE THIN FILM ON STAINLESS-STEEL SURFACE
Surface Review and Letters, 2002Co-Authors: Sangwoon Moon, Sukmin Chung, Chongdo Park, Tai-hee KangAbstract:We investigated the various oxidation conditions of stainless-steel surface using synchrotron radiation photoemission spectroscopy. Stainless-steel samples are oxidized at 450–550°C in various oxygen partial pressures. Increasing the annealing temperature from 450°C to 550°C, the trivalent chromium concentration in the surface increased and iron oxides decreased. The PES spectra from stainless steels oxidized at 550°C show that there exists the critical oxygen partial pressure, Torr. Below this critical pressure, the oxide formed mainly consists of chromium oxide, while the oxide formed mainly consists of iron oxide above the critical pressure. The oxidation behavior is in good agreement with the Ellingham Diagram (a free-energy/temperature Diagram).
Huiyu Li - One of the best experts on this subject based on the ideXlab platform.
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determination of gibbs free energy of formation from elements for ca4fe9o17 by solid state galvanic cell
Metallurgical and Materials Transactions B-process Metallurgy and Materials Processing Science, 2015Co-Authors: Huiyu LiAbstract:Aiming to fill the thermodynamic blank in CaO-FeO-Fe2O3 system, the determination of the Gibbs free energy of formation from elements for ternary Ca4Fe9O17 was carried out using a solid-state galvanic cell with air and calcium zirconate material, respectively, as the reference electrode and electrolyte. The ternary system Ca2Fe2O5-CaFe2O4-Ca4Fe9O17 was selected as the measuring electrode and its equilibrium was confirmed. The essential thermodynamic data of Ca2Fe2O5 and CaFe2O4 were cited from the reassessed data from a previous investigation. The reversible electromotive forces of the cell were determined from 1273 K to 1473 K (1000 °C to 1200 °C). The Gibbs free energy of formation from elements for Ca4Fe9O17 was derived and given by: $$ \Delta_{\text{f}} G_{\text{m}}^{ \circ } ({\text{Ca}}_{4} {\text{Fe}}_{9} {\text{O}}_{17} ) = -6218.862 \times 10^{3} + 1247.762T + 31.32T\ln T \pm 2694\;({\text{J}}\,{\text{mol}}^{-1} ) $$ The increment of enthalpy and entropy of formation from elements for Ca4Fe9O17 at 298 K (25 °C) are calculated to be \( \Delta_{\text{f}} H_{{{\text{m}},298}}^{ \circ } = -6209.529 \times 10^{3} \;({\text{J}}\,{\text{mol}}^{-1} ) \) and \( \Delta_{\text{f}} S_{{{\text{m}},298}}^{ \circ } = -1038.009\;({\text{J}}\,{\text{mol}}^{-1} \,{\text{K}}^{-1} ) \). The Ellingham Diagram was developed in temperature range 1273 K to 1473 K (1000 °C to 1200 °C). The oxygen potential of Ca4Fe9O17 was found to be slightly higher than CaFe2O4 and much higher than Ca2Fe2O5.
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Determination of Gibbs Free Energy of Formation from Elements for Ca 4 Fe 9 O 17 by Solid-state Galvanic Cell
Metallurgical and Materials Transactions B-process Metallurgy and Materials Processing Science, 2014Co-Authors: Huiyu LiAbstract:Aiming to fill the thermodynamic blank in CaO-FeO-Fe2O3 system, the determination of the Gibbs free energy of formation from elements for ternary Ca4Fe9O17 was carried out using a solid-state galvanic cell with air and calcium zirconate material, respectively, as the reference electrode and electrolyte. The ternary system Ca2Fe2O5-CaFe2O4-Ca4Fe9O17 was selected as the measuring electrode and its equilibrium was confirmed. The essential thermodynamic data of Ca2Fe2O5 and CaFe2O4 were cited from the reassessed data from a previous investigation. The reversible electromotive forces of the cell were determined from 1273 K to 1473 K (1000 °C to 1200 °C). The Gibbs free energy of formation from elements for Ca4Fe9O17 was derived and given by: $$ \Delta_{\text{f}} G_{\text{m}}^{ \circ } ({\text{Ca}}_{4} {\text{Fe}}_{9} {\text{O}}_{17} ) = -6218.862 \times 10^{3} + 1247.762T + 31.32T\ln T \pm 2694\;({\text{J}}\,{\text{mol}}^{-1} ) $$ The increment of enthalpy and entropy of formation from elements for Ca4Fe9O17 at 298 K (25 °C) are calculated to be \( \Delta_{\text{f}} H_{{{\text{m}},298}}^{ \circ } = -6209.529 \times 10^{3} \;({\text{J}}\,{\text{mol}}^{-1} ) \) and \( \Delta_{\text{f}} S_{{{\text{m}},298}}^{ \circ } = -1038.009\;({\text{J}}\,{\text{mol}}^{-1} \,{\text{K}}^{-1} ) \). The Ellingham Diagram was developed in temperature range 1273 K to 1473 K (1000 °C to 1200 °C). The oxygen potential of Ca4Fe9O17 was found to be slightly higher than CaFe2O4 and much higher than Ca2Fe2O5.
K. T. Jacob - One of the best experts on this subject based on the ideXlab platform.
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Use of CaCl_2 as a chlorinating agent for oxides — A thermodynamic analysis
Mining Metallurgy & Exploration, 1992Co-Authors: N. Rajmohan, K. T. JacobAbstract:Presented is a thermodynamic feasibility analysis of extracting base metal chlorides from low-grade, multi-metallic oxide ores using CaCl_2 as a chlorinating agent in the presence of SO_2 and O_2. The oxides react to form corresponding chlorides, while CaCl_2 is converted to CaSO_4. The Ellingham Diagram is used for comparing the standard Gibbs’ free energy change for the sulfation-chlorination reaction of a large number of oxides. Except for alumina, silica and chromia, most of the other metal oxides will be converted to their respective chlorides. The volatile chlorides can be condensed, and the chlorides present in the condensed state can be leached. A process is proposed that uses a nontoxic chlorinating agent and gives an efficient separation of the metallic values from the gangue.
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Use of CaC12 as a chlorinating agent for oxides - A thermodynamic analysis
Mining Metallurgy & Exploration, 1992Co-Authors: N. Rajmohan, K. T. JacobAbstract:Presented is a thermodynamic feasibility analysis of extracting base metal chlorides fiom low-grade,multimetallic oxide ores using CaClz as a chlorinating agent in the presence of SOz undoz. The oxides react to form corresponding chlorides, while CaClz is converted to CaS04. The Ellingham Diagram is usedfor comparing the standard Gibbs' fiee energy chanlpef or the su(fation-chlorinationr eaction of a large number of oxides. Except for alumina, silica and chromia, most of the other metal oxides will be converted to their respective chlorides. The volatile chlorides can be condensed, and the chlorides present in the condensed state can be leached. A process is proposed that uses a nontoxic chlorinating agent and gives an eficient sepurutiort cftlte metallic vuluesfr.om the garlgue.
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The standard molar Gibbs energy of formation of YbPt3 and LuPt3 intermetallics
The Journal of Chemical Thermodynamics, 1990Co-Authors: K. T. Jacob, Yoshio WasedaAbstract:Abstract The standard molar Gibbs energies of formation of YbPt3 and LuPt3 intermetallic compounds have been measured in the temperature range 880 K to 1100 K using the solid-state cells: Ta|Yb+YbF 2 |CaF 2 |YbPt 3 +Pt+YbF 2 |Ta, and Ta|Lu+LuF 3 |CaF 2 |LuPt 3 +Pt+LuF 3 |Ta, The trifluoride of Yb is not stable in equilibrium with Yb or YbPt3. The results can be expressed by the equations: Δ f G m ° ( YbPt 3 ) (J· mol −1 ) =−322100+0.39( T K )±400, Δ f G m ° ( LuPt 3 ) (J· mol −1 ) =−366800+3.82( T K )±400. The standard molar Gibbs energy of formation of LuPt3 is −41.1 kJ · mol−1 more negative than that for YbPt3 at 1000 K. Ytterbium is divalent in the pure metal and trivalent in the intermetallic YbPt3. The energy required for the promotion of divalent Yb to the trivalent state is responsible for the less negative ΔfGmo of YbPt3. The enthalpies of formation of the two intermetallics are in reasonable agreement with Miedema's model. Because of the extraordinary stability of these compounds it is possible to reduce oxides of Yb and Lu with hydrogen in the presence of platinum at T K > 1473 . The equilibrium chemical potential of oxygen corresponding to the reduction of Yb2O3 and Lu2O3 by hydrogen in the presence of platinum is presented in the form of an Ellingham Diagram.
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The standard molar Gibbs energy of formation of $YbPt_3$ and $LuPt_3$ intermetallics
1990Co-Authors: K. T. Jacob, Yoshio WasedaAbstract:The standard molar Gibbs energies of formation of $YbPt_3$ and $LuPt_3$ intermetallic compounds have been measured in the temperature range 880 K to 1100 K using the solid-state cells: $Ta\mid\hspace{2mm}Yb+YbF_2\mid\hspace{2mm}CaF_2\mid\hspace{2mm}YbPt_3Pt+YbF_2\mid\hspace{2mm}Ta,$ and $Ta\mid\hspace{2mm}Lu+LuF_3\mid\hspace{2mm}CaF_2\mid\hspace{2mm}LuPt_3+Pt+LuF_3\mid\hspace{2mm}Ta$, The trifluoride of Yb is not stable in equilibrium with Yb or $YbPt_3$. The results can be expressed by the equations: $\Delta_fG_m\hspace{1mm}^°(YbPt_3)/(J·mol^{-1})=-322100+0.39(T/K)\pm400$, $\Delta_fG_m \hspace{1mm}^°(LuPt_3)/(J·mol^{-1})=-366800+3.82(T/K)\pm 400$. The standard molar Gibbs energy of formation of $LuPt_3 is -41.1 kJ – mol^{-1}$more negative than that for $YbPt_3$ at 1000 K. Ytterbium is divalent in the pure metal and trivalent in the intermetallic $YbPt_3$. The energy required for the promotion of divalent Yb to the trivalent state is responsible for the less negative $\Delta_f\hspace{2mm}G_m\hspace{1mm} ^o $ of $YbPt_3$. The enthalpies of formation of the two intermetallics are in reasonable agreement with Miedema's model. Because of the extraordinary stability of these compounds it is possible to reduce oxides of Yb and Lu with hydrogen in the presence of platinum at $T/K>1473$. The equilibrium chemical potential of oxygen corresponding to the reduction of $Yb_2O_3$ and $Lu_2O_3$ by hydrogen in the presence of platinum is presented in the form of an Ellingham Diagram.