X-ray photoelectron spectroscopy (XPS) and secondary mass ion spectrometry (SIMS) have been used ... more X-ray photoelectron spectroscopy (XPS) and secondary mass ion spectrometry (SIMS) have been used for studying surface layers formed by selective oxidation of titanium in high-purity copper-titanium alloys. Sheets of copper-0.5, 1.0, 1.5, 2.0 and 3.4 mass% titanium alloys were annealed at 873 K under a low partial pressure of oxygen. XPS results indicate titanium enrichment on the surface side of a sample to form titanium oxides. With increasing bulk concentration of titanium, the amount of titanium oxides formed on the sample surface increased, while the amount of metallic copper decreased. SIMS depth profiles of these samples showed that titanium oxides are formed in a surface layer less than one micrometer thick, and a titanium-depleted zone is formed beneath the surface layer containing titanium oxides. A concentration profile of titanium formed beneath the titanium-depleted zone was found to be described by outward diffusion of titanium in the matrix, indicating that the oxidation process is mainly controlled by diffusion of titanium in copper.
Glass-forming composition ranges in the alloy system Zr-Ni-Al are predicted by applying Miedema's... more Glass-forming composition ranges in the alloy system Zr-Ni-Al are predicted by applying Miedema's semi-empirical method. The compositional dependence of the formation enthalpies of amorphous ∆H(Amo), solid solution ∆H(SS), and intermetallic compound phases ∆H(Comp) is calculated. We propose that the enthalpy difference parameters of ∆H(SS) − ∆H(Amo), ∆H(Amo) − ∆H(Comp) and simple criteria, including electronegativities, can be used to predict the glass-forming composition ranges (GFR) and the dominant factors determining the glass-forming ability (GFA). The wide GFR in the system, apart from the Al-rich region, and the tendency of the intermetallic compounds to form and constrain any extension of the GFR, are clearly predicted by a combining evaluation of these parameters and the simple criteria. The large negative heat of mixing, the atomic size difference among the constituent elements, and the short-range order stabilize the glassy phase leading to a high GFA of the alloy system. Furthermore, the composition dependence of crystallization temperatures T x and the glass transition temperatures T g can be estimated on the basis of the enthalpy values. Results compare well with the experimental data.
The distribution of zinc cation between crystallographically nonequivalent positions in ZnFe204 h... more The distribution of zinc cation between crystallographically nonequivalent positions in ZnFe204 has been determined by anomalous X-ray scattering near the Zn K absorption edge. Measured intensity ratio with two energies close to the edge can be quantitatively explained only by assigning all zinc cations to the tetrahedral position in the approximately cubic close packed array of oxygen ions. A similar conclu sion has also been reached for ZnxFe3-x04 solid solutions with x = 0.73, 0.54 and 0.35 employing the im proved X-ray method. This is consistent with the EXAFS results which indicate an almost unchanged environmental structure around zinc cation in these solid solutions.
The total structure factors, S(q), of liquid Ag-In alloys have been derived by X-ray diffraction ... more The total structure factors, S(q), of liquid Ag-In alloys have been derived by X-ray diffraction measurements. The concentration dependence of the first peak position is divided into three groups; on going from Ag to 70 at% Ag, the peak position decreases linearly and it goes to decrease with a more rapid proportion for the concentration range from 70 to 40
Metallic Ru has been found to coexist separately with SrO, RuO2 and the interoxide phases, Sr2RuO... more Metallic Ru has been found to coexist separately with SrO, RuO2 and the interoxide phases, Sr2RuO4, Sr3Ru2O7, Sr4Ru3O10 and SrRuO3, present along the pseudo-binary system SrORuO2 at 1300 K. The standard Gibbs energies of formation (Δf (ox) G°) of the four ...
As part of a systematic study on the thermodynamic properties of complex nitrides, phase equilibr... more As part of a systematic study on the thermodynamic properties of complex nitrides, phase equilibria of the system Li-M-N (M = Mg, Al, Ga) at 900 K were investigated. An attempt to determine the thermodynamic properties of complex nitrides was made by using the galvanic cell method, which utilizes LiMgN as an electrolyte under nitrogen atmosphere. The electromotive force (Emf) of the cell at temperatures between 800 and 1100 K was measured. While the Emf of the cell at 900 K was measured to be 0.137 V, data discrepancies of f0.03V were found. It was difficult to determine temperature dependence of the Emf. The Gibbs energy change for the reaction, 113 Li3N (s) + 113 Mg3N2 (s) = LiMgN (s), at 900 K was determined to be AGO, (LiMgN) = -13.2 (k2.9) Wmol. Using thermodynamic information on the binary nitride fiom literature, the standard Gibbs energy of LiMgN was derived to be AGOf (LiMgN)= -121 kJ at 900 K. The thermodynamic stability range of nitride was discussed by constructing isothermal chemical potential diagrams that provide a better understanding of the stability region of the LiMgN phase. The diagram was found to be in good agreement with the isothermal phase diagram determined by the alloy equilibration method. Although the obtained data includes large uncertainties, the results provide a better understanding of the thermodynamic stability of nitrides. The potential application of this complex nitride to nitrogen chemical sensors or a medium for controlling nitrogen potential is also shown.
X-ray photoelectron spectroscopy (XPS) and secondary mass ion spectrometry (SIMS) have been used ... more X-ray photoelectron spectroscopy (XPS) and secondary mass ion spectrometry (SIMS) have been used for studying surface layers formed by selective oxidation of titanium in high-purity copper-titanium alloys. Sheets of copper-0.5, 1.0, 1.5, 2.0 and 3.4 mass% titanium alloys were annealed at 873 K under a low partial pressure of oxygen. XPS results indicate titanium enrichment on the surface side of a sample to form titanium oxides. With increasing bulk concentration of titanium, the amount of titanium oxides formed on the sample surface increased, while the amount of metallic copper decreased. SIMS depth profiles of these samples showed that titanium oxides are formed in a surface layer less than one micrometer thick, and a titanium-depleted zone is formed beneath the surface layer containing titanium oxides. A concentration profile of titanium formed beneath the titanium-depleted zone was found to be described by outward diffusion of titanium in the matrix, indicating that the oxidation process is mainly controlled by diffusion of titanium in copper.
Glass-forming composition ranges in the alloy system Zr-Ni-Al are predicted by applying Miedema's... more Glass-forming composition ranges in the alloy system Zr-Ni-Al are predicted by applying Miedema's semi-empirical method. The compositional dependence of the formation enthalpies of amorphous ∆H(Amo), solid solution ∆H(SS), and intermetallic compound phases ∆H(Comp) is calculated. We propose that the enthalpy difference parameters of ∆H(SS) − ∆H(Amo), ∆H(Amo) − ∆H(Comp) and simple criteria, including electronegativities, can be used to predict the glass-forming composition ranges (GFR) and the dominant factors determining the glass-forming ability (GFA). The wide GFR in the system, apart from the Al-rich region, and the tendency of the intermetallic compounds to form and constrain any extension of the GFR, are clearly predicted by a combining evaluation of these parameters and the simple criteria. The large negative heat of mixing, the atomic size difference among the constituent elements, and the short-range order stabilize the glassy phase leading to a high GFA of the alloy system. Furthermore, the composition dependence of crystallization temperatures T x and the glass transition temperatures T g can be estimated on the basis of the enthalpy values. Results compare well with the experimental data.
The distribution of zinc cation between crystallographically nonequivalent positions in ZnFe204 h... more The distribution of zinc cation between crystallographically nonequivalent positions in ZnFe204 has been determined by anomalous X-ray scattering near the Zn K absorption edge. Measured intensity ratio with two energies close to the edge can be quantitatively explained only by assigning all zinc cations to the tetrahedral position in the approximately cubic close packed array of oxygen ions. A similar conclu sion has also been reached for ZnxFe3-x04 solid solutions with x = 0.73, 0.54 and 0.35 employing the im proved X-ray method. This is consistent with the EXAFS results which indicate an almost unchanged environmental structure around zinc cation in these solid solutions.
The total structure factors, S(q), of liquid Ag-In alloys have been derived by X-ray diffraction ... more The total structure factors, S(q), of liquid Ag-In alloys have been derived by X-ray diffraction measurements. The concentration dependence of the first peak position is divided into three groups; on going from Ag to 70 at% Ag, the peak position decreases linearly and it goes to decrease with a more rapid proportion for the concentration range from 70 to 40
Metallic Ru has been found to coexist separately with SrO, RuO2 and the interoxide phases, Sr2RuO... more Metallic Ru has been found to coexist separately with SrO, RuO2 and the interoxide phases, Sr2RuO4, Sr3Ru2O7, Sr4Ru3O10 and SrRuO3, present along the pseudo-binary system SrORuO2 at 1300 K. The standard Gibbs energies of formation (Δf (ox) G°) of the four ...
As part of a systematic study on the thermodynamic properties of complex nitrides, phase equilibr... more As part of a systematic study on the thermodynamic properties of complex nitrides, phase equilibria of the system Li-M-N (M = Mg, Al, Ga) at 900 K were investigated. An attempt to determine the thermodynamic properties of complex nitrides was made by using the galvanic cell method, which utilizes LiMgN as an electrolyte under nitrogen atmosphere. The electromotive force (Emf) of the cell at temperatures between 800 and 1100 K was measured. While the Emf of the cell at 900 K was measured to be 0.137 V, data discrepancies of f0.03V were found. It was difficult to determine temperature dependence of the Emf. The Gibbs energy change for the reaction, 113 Li3N (s) + 113 Mg3N2 (s) = LiMgN (s), at 900 K was determined to be AGO, (LiMgN) = -13.2 (k2.9) Wmol. Using thermodynamic information on the binary nitride fiom literature, the standard Gibbs energy of LiMgN was derived to be AGOf (LiMgN)= -121 kJ at 900 K. The thermodynamic stability range of nitride was discussed by constructing isothermal chemical potential diagrams that provide a better understanding of the stability region of the LiMgN phase. The diagram was found to be in good agreement with the isothermal phase diagram determined by the alloy equilibration method. Although the obtained data includes large uncertainties, the results provide a better understanding of the thermodynamic stability of nitrides. The potential application of this complex nitride to nitrogen chemical sensors or a medium for controlling nitrogen potential is also shown.
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Papers by Yoshio Waseda