Self-diffusion Coefficients Of Cations Research Articles

Cationic Self-Diffusion in Molten (Tl-Na)NO3 and (Tl-Rb)NO3 Systems

Abstract The cationic self-diffusion coefficients in molten (Tl-Na)NO3 and (Tl -Rb)NO3 systems were investigated as a function of temperature and concentration. The obtained data were examined from the viewpoint of polarization and ionic size effects.

Self-Diffusion Coefficients in the Molten AgNO3-AlkNO3 Systems

The cationic self-diffusion coefficients in the fused (Ag-Li) NO3, (Ag-Rb) NO3 and (Ag-Cs) NO3 systems have been investigated as a function of composition and temperature. The deviation from linearity of the D+ vs. composition isotherms in the (Ag-Alk) NO3 series is discussed in terms of ionic interactions. Quantitative relationships between D+ and ionic size and mass have been established

Cation self-diffusion in single-crystal MgO

Cation self-diffusion coefficients have been obtained for MgO in an argon atomosphere over a temperature range 1000–2400°C from concentration gradients determined with the aid of mass spectrometry. The problems associated with use of the short-lived radioisotope 28Mg were avoided by employing the stable isotope 26Mg as a tracer. Samples were prepared utilizing vapor-exchange, thick-film, and semi-infinite source boundary conditions at high, intermediate, and low temperatures, respectively, and were protected from contamination and volatilization by encapsulation in cylinders of pressed MgO powder. No significant difference in transport behavior was noted between crystals of moderate quality and those of the highest purity presently available. The temperature dependence of the diffusion coefficients may be represented by an activation energy of 2.76±0.08 eV and D0 of 4.19 × 10−4 cm2/sec. These parameters are comparable to those previously reported for impurity ion diffusion. The activation energy obtained is interpreted as that for cation migration. Previous measurements of cation self-diffusion coefficients obtained with the short-lived radisotope 28Mg are an order of magnitude larger and had been interpreted as intrinsic diffusion. The discrepency is attributed to doping introduced by the 28Si decay product of 28Mg.

Diffusion in the System K2O‐SrO‐SiO2: II, Cation Self‐Diffusion Coefficients*

Cation self‐diffusion coefficients were measured in the system 0.2K2O‐0.2SrO‐0.6SiO2 (wt fraction) by introducing a slab of glass previously irradiated in a reactor between two slabs of unirradiated glass. By heating the specimens for various times at temperatures above Tg, etching them sequentially, and counting the β‐ and γ‐activity, self‐diffusion coefficients for K and Sr were measured, and an upper limit for that of Si was estimated. At 530°C<T<830°C, DK≅36.5 exp (‐40,800/RT) and DSr≅0.17 exp (‐42,700/RT), although the fit to Arrhenius behavior was poor. At 750°C, the self‐diffusion coefficient for the Na impurity was almost the same as that for K, whereas that of Si was less than that of Sr.

Cationic Self-Diffusion in Calcia-Stabilized Zirconia

Self-diffusion of Zr in 12 and 16 mol.% CaO and of Ca in 16 mol.% CaO cubic zirconia was measured by the sectioning technique from 1700° to 2150°C. Lattice self-diffusion coefficients are: Autoradiographs show rapid grain boundary diffusion. DB is estimated as <105DL between 1800° and 2150°C. The low cation self-diffusion coefficients are compared with the high anion rate, and their effect on the diffusion-controlled properties of zirconia is discussed.