Ryokichi Shimpo
University of Tokyo
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Metallurgical and Materials Transactions B-process Metallurgy and Materials Processing Science | 1994
Ryokichi Shimpo; Yasushi Nakamura
The Gibbs energy changes for syntheses of the interoxide compounds in the Bi-Ca-O system have been determined from thermogravimetry and solid-state electrochemical measurements in the temperature range 850 to 1000 K. Thermogravimetry was used in the measurements of CO2 partial pressures equilibrated with calcium carbonate and a pair of the compounds in the Bi-Ca-O system: Bi6Ca7O16 + Bi10Ca7O22 (Bi10Ca7O22 + Bi2CaO4 or Bi2CaO4 + Bi14Ca5O26). Cells employing yttria-stabilized zirconia as electrolyte were used in the study of Bi6Ca7O16 where an intermetallic compound BiPt was employed for the protection of Pt lead wire of the cell and to lower the vaporization of Bi in the cell. Based on the results of thermogravimetric study and electromotive force (emf) measurement, the Gibbs energy changes were calculated for the reactions in which the respective compounds were synthesized from Bi2O3 and CaO.
Metallurgical and Materials Transactions B-process Metallurgy and Materials Processing Science | 1994
Ryokichi Shimpo; Yasushi Nakamura
The Gibbs energy changes for the syntheses of the interceramic compounds of BaCuO2 and BaCu2O2 were investigated as a basic study in the Y-Ba-Cu-O system that includes a superconductor, YBa2Cu3O6.5+x. For the compound BaCuO2, thermogravimetry with CO2-O2-N2 gas mixtures was employed, and equilibrium temperatures were determined at which CO2 partial pressures in the gas mixtures were equilibrated with mixed powder of BaCuO2, CuO, and BaCO3. The Gibbs energy change for the reaction of BaCO3 + CuO = BaCuO2 + CO2 was determined from the relation between CO2 partial pressure and equilibrium temperature, taking into consideration the effect of CO2 dissolution in BaCuO2. For the study on BaCu2O2, electromotive force (emf) measurement using yttria-stabilized zirconia solid electrolyte was conducted. A technique using two cells was applied to the emf measurement for minimizing the effect of dispersion of oxygen from samples, and the Gibbs energy change for the reaction of BaCuO2 + CuO = BaCu2O2 + 1/2O2 was decided from the measured O2 partial pressure.
Metallurgical and Materials Transactions A-physical Metallurgy and Materials Science | 2007
Ryokichi Shimpo; Y. Nakamura
Numerous reports have been published on the superconductivity, structure, and physical properties of the Bi-Sr-Ca-Cu-O system, including the ceramic superconductors of Bi[sub 2]Sr[sub 2]Ca[sub 2]Cu[sub 3]O[sub y] and Bi[sub 2]Sr[sub 2]CaCu[sub 2]O[sub y]. On the phase diagrams of the system, numbers of studies have so far been presented, but there exist several regions in the proposed phase diagram of the Bi[sub 2]O[sub 3]-SrO-CaO quasiternary system, which have been presented by several investigators, are different from each other because the ternary system includes a number of solid solution phases of which the phase equilibrium relations are complicated. In this study, isothermal sections of the phase diagram for the Bi[sub 2]O[sub 3]-SrO-CaO ternary system at 973 and 1,023 K have been investigated. Experiments were conducted in air, because this system does not include copper oxides and, therefore, it is considered that the oxygen contents in the interceramic compounds in this system are substantially not affected by the oxygen potential.
Metallurgical transactions. A, Physical metallurgy and materials science | 1993
Ryokichi Shimpo; Yasushi Nakamura
Numerous reports have been published on the superconductivity, structure, and physical properties of the Bi-Sr-Ca-Cu-O system, including the ceramic superconductors of Bi[sub 2]Sr[sub 2]Ca[sub 2]Cu[sub 3]O[sub y] and Bi[sub 2]Sr[sub 2]CaCu[sub 2]O[sub y]. On the phase diagrams of the system, numbers of studies have so far been presented, but there exist several regions in the proposed phase diagram of the Bi[sub 2]O[sub 3]-SrO-CaO quasiternary system, which have been presented by several investigators, are different from each other because the ternary system includes a number of solid solution phases of which the phase equilibrium relations are complicated. In this study, isothermal sections of the phase diagram for the Bi[sub 2]O[sub 3]-SrO-CaO ternary system at 973 and 1,023 K have been investigated. Experiments were conducted in air, because this system does not include copper oxides and, therefore, it is considered that the oxygen contents in the interceramic compounds in this system are substantially not affected by the oxygen potential.
Canadian Metallurgical Quarterly | 1986
Ryokichi Shimpo; Sakichi Goto; Osamu Ogawa; Iwazo Asakura
Metallurgical and Materials Transactions B-process Metallurgy and Materials Processing Science | 1997
Ryokichi Shimpo; Osamu Ogawa; Yuichi Fukaya; Takehiro Ishikawa
Journal of The Japan Institute of Metals | 1990
Ryokichi Shimpo; Yasushi Nakamura
Metallurgical and Materials Transactions A-physical Metallurgy and Materials Science | 1993
Ryokichi Shimpo; Osamu Ogawa; Sakichi Goto
Archive | 2008
Shigeo Hoshino; Ryokichi Shimpo; Yasuyuki Tanaka
Journal of The Japan Institute of Metals | 1992
Sei Kimura; Ryokichi Shimpo; Yasushi Nakamura