Yasumichi Oishi

Self‐diffusion coefficients of oxygen ion in single crystals of MgO · n Al2O3 spinels

Oxygen self‐diffusion coefficients in single crystal spinels were determined for three compositions of MgO · Al2O3, MgO · 1.2Al2O3, and MgO · 2.2Al2O3 by a gas‐solid exchange technique utilizing 18O as a tracer. The temperature dependence of the self‐diffusion coefficient for MgO · Al2O3 was expressed as D = 0.89 exp(− 105 × 103/RT) cm2/sec. The self‐diffusion coefficients for MgO · 1.2Al2O3 and MgO · 2.2Al2O3 were close to that for MgO · Al2O3, which was interpreted as being due to intrinsic diffusion. The determined self‐diffusion coefficient of oxygen ion was smaller by several orders of magnitude than that of magnesium ion and was closer to the apparent diffusion coefficients calculated from the sintering rates. The influence of surface exchange reaction was noticed in determining the self‐diffusion coefficient.

Self-diffusion of oxygen in single crystal alumina

The self‐diffusion coefficient of oxygen in (polished slices of a Verneuil) single‐crystal alumina was determined in the temperature range 1500–1770 °C by means of the gas–solid isotope exchange technique. The results were represented by D=1.12×103 exp (−155×103/RT) cm2/s. The activation energy was interpreted to be for intrinsic diffusion. By comparison of the results with the oxygen self‐diffusion coefficients previously reported for crushed particles of a Verneuil alumina and a vapor‐grown alumina, the extrinsic diffusion exhibited by the crushed particles was confirmed to be due to a dislocation enhancement process.

Zr-Hf interdiffusion in polycrystalline Y2O3-(Zr+Hf)O2

Lattice and grain-boundary interdiffusion coefficients were calculated from the concentration distributions determined for Zr-Hf interdiffusion in polycrystalline 16Y2O3·84(Zr1−x Hfx)O2 withx=0.020 and 0.100. The lattice interdiffusion coefficients were described byD=0.031 exp [−391 (kJ mol−1)/RT] cm2 sec−1 and the grain-boundary diffusion parameters byσD′=1.5×10−6exp [−309(kJ mol−1)/RT] cm3 sec−1 in the temperature range 1584–2116° C. Comparison of the results with those for the systems CaO-(Zr+Hf)O2 and MgO-(Zr+Hf)O2 indicated that the Zr self-diffusion coefficient was insensitive to the dopants in the fluorite-cubic ZrO2 solid solutions.

Self-diffusion coefficient of lithium in lithium oxide

Abstract The self-diffusion coefficient of lithium ion in Li2O was determined in the range 515–1288°C by means of the sectioning technique using 6Li as the tracer. The Arrhenius relation was represented by D = 4.06 × 10 3 exp( −58.2 × 10 3 RT ) cm 2 s above 1000°C and by D = 3.25 × 10 −3 exp( −23.4 × 10 3 RT ) cm 2 /s below 1000°C. The characteristics of lithium diffusion in Li2O, which is antifluorite cubic, was discussed in comparison with anion diffusion in CaF2 and other fluorite-cubic crystals.

Self‐diffusion of oxygen in single crystal thorium oxide

Self‐diffusion coefficients of the oxygen ion in a ThO2 single crystal were determined in the temperature range 845–1646°C by the gas–solid isotopic exchange technique using 18O as a tracer. The self‐diffusion coefficients determined in the higher temperature range were represented as D=5.73×10−2 exp(−49.9×103/RT) cm2/sec and interpreted to be for intrinsic diffusion due to Frenkel‐type defects. Those determined in the lower temperature range were represented as D=1.00×10−6 exp(−17.6×103/RT) cm2/sec and interpreted for extrinsic diffusion. By using these data, it was elucidated that the charge carrier for ionic conduction in ThO2 was the oxygen ion. Activation energies for oxygen permeation in ThO2 and for oxidation of thorium metal were compared with that for oxygen self‐diffusion in ThO2.

Grain‐boundary enhanced interdiffusion in polycrystalline CaO‐stabilized zirconia system

A solution of the flux density equation is presented for grain−boundary enhanced diffusion in a polycrystalline system when the penetration depth is large relative to the grain size. The solution is applied to interdiffusion between 13 and 19 mol% CaO‐stabilized zirconia polycrystals from 1375–1650 °C. Lattice interdiffusion coefficients calculated from the concentration distributions are slightly larger than the previously reported self‐diffusion coefficients of the individual cations.

Oxygen Self-Diffusion in Cubic ZrO2 Solid Solutions

Because of the interest in their application to solid electrolyte, electrical conductivity has been extensively determined for various stabilized ZrO2 by many investigators. In contrast, direct determination of the oxygen tracer diffusion coefficient has been made only for CaO-stabilized ZrO2 by Kingery et al. (1959) and later by Simpson and Carter (1966). Agreement of the oxygen self-diffusion coefficient with the electrical conductivity determined by Kingery et al. proved that CaO-stabilized ZrO2 is an oxygen ionic conductor due to the temperature-independent oxygen vacancies resultant from substitution of divalent Ca ions for Zr ions in the fluorite structure. The determined activation energy, 127 kJ/mol, was interpreted to be the migration energy for the oxygen ion.

Cation interdiffusion in polycrystalline fluorite-cubic solid solutions

Abstract A grain-boundary enhanced diffusion model was applied to the cation interdiffusion in polycrystalline fluorite-cubic solid solutions to determine separately the lattice and grain-boundary interdiffusion coefficients. The Zr-Hf lattice interdiffusion coefficients determined for the 16 CaO · 84(Zr 1−x Hf x )O 2 system in the temperature range of 1502–2083°C were described by D = rm 0.023 exp(−90 × 10 3 /RT) cm 2 /s and those for the 14 MgO · 86(Zr 1−x Hf x )O 2 system in the temperature range of 1680–2083°C by D = 0.033 exp(−91 × 10 3 /RT ) cm 2 /s. The two results were close to the Zr lattice self-diffusion coefficient reported for CaO-stabilized zirconia.

Oxygen self-diffusion in Fe-doped MgO single crystals

Oxygen self‐diffusion coefficients in Fe‐doped MgO single crystals were determined by an isotope exchange technique. The results indicated dopant‐insensitive diffusion, which was interpreted as due to the vacancy pair mechanism.

Relation between self-diffusion coefficients and interdiffusion coefficients in methanol-carbon tetrachloride and ethanol-carbon tetrachloride systems

Darkens binary diffusion equation was tested between interdiffusion coefficient and self‐diffusion coefficients for thermodynamically nonideal methanol‐carbon tetrachloride and ethanol‐carbon tetrachloride systems in which molecular association of the alcohols is known to occur. When the thermodynamic factor was calculated from equilibrium vapor pressures, Darkens equation did not hold for the two systems, but the thermodynamic factor approximately calculated from the mean degree of association of the alcohol better satisfied the equation for the systems within the low alcohol concentration range. Self‐diffusion coefficients of the respective components necessary for the present testing were measured for the methanol‐carbon tetrachloride system at 25°C. By assuming Darkens relation, mean degrees of association of the alcohols were reversely calculated for the high alcohol concentration range of the two systems.