Abstract: The influence of thermodynamic constraints like the size, depletion, surface tension and kinetic constraints like energy barrier for diffusion on nonsteady separation kinetics in binary nanopowder is investigated. Here we present a numeric analysis of size hysteresis and its peculiarities using the standard kinetic equation approach.
Abstract: Anelastic effects caused by carbon and vacancy diffusion in Fe3Al based alloys with and without strong carbide forming elements (Ti and Nb) are investigated by internal friction measurements. The decrease of the Snoek peak in Fe–26Al–2Ti and Fe–26Al–0.3Nb alloys with respect to the Fe–26Al alloy is related to a decrease in the amount of interstitially dissolved carbon (C). The so-called X peak, which is observed in the Fe–26Al alloy, also almost disappears after alloying. In order to elucidate the vacancy contribution to the origin of the X peak radiotracer measurements of 59Fe diffusion were performed. The results indicate that the change in the interstitially dissolved C concentration is the main reason of the observed changes in the X peak, although a certain influence of Ti and Nb alloying on the total vacancy concentration may be deduced from the diffusion study.
Abstract: The peculiarities of practical application of effective interdiffusion coefficients of
components for calculating diffusion paths in ternary systems are analysed. It is shown that infinite values of the interdiffusion coefficients at zero concentration gradient’s points do not remarkably affect the accuracy of calculation in the case of a correct choice of variables. At zero-flux planes where the respective effective interdiffusion coefficient is equal to zero, no calculation problems arise, as evidently zero-flux planes can occur simultaneously only for one of the components. The
results of calculation of diffusion paths for diffusion couples in the ternary systems Cu-Fe-Ni and Co-Fe-Ni using respective effective interdiffusion coefficients are presented. These results demonstrate a good accuracy of such kind of calculations even in the case of very strong deviation from linearity of the diffusion path.
Abstract: This work is devoted to simulation of interstitial atom diffusion in fcc metals with point
defects. We used the molecular static and the Monte Carlo methods. An activation barrier set for different configurations of the carbon–vacancy complexes is simulated by the method of the molecular static (MS). Then we calculate atom jump rates for these configurations. The simulation of the carbon and vacancy migration in an fcc metal is realized on the basis of obtained atom jump rates by using the Monte-Carlo (MC) method. In particular, the calculations were made for the system of the nickel-carbon. In the result of that interstitial atom diffusion coefficient has been obtained at different temperatures.
Abstract: Gallium grain boundary (GB) diffusion of Ga in polycrystalline magnesium was
investigated by radiotracer residual activity technique using 67Ga isotope. The diffusion measurements were carried out under conditions of Harrison’s B-type kinetics in temperature range 639 – 872 K. An approximate evaluation procedure was proposed to calculate both volume diffusion coefficient Dv and GB diffusivity P = s dDb (s is the segregation factor, d the GB width and Db the GB diffusion coefficient). The obtained results showed the following linear Arrhenius relationships: Dv = 1.2 × 10-4 × exp (–134.3 kJ mol-1/RT) m2 s-1 and P = 3.8 × 10-9 × exp (–94.9 kJ mol-1/RT) m3 s-1, where R is universal gas constant and T the temperature. Obtained results were compared with literature data on Mg self-diffusion and with In impurity diffusion in magnesium.
Abstract: The La1-xSrxCo0.2Fe0.6Ni0.2O3-d, La1-xSrxCo0.4Fe0.4Ni0.2O3-d and
La1-xSrxCo0.2Fe0.4Ni0.4O3-d perovskites were synthesized with Sr contents 0.1 ≤ x ≤ 0.3 using precursors obtained by citric acid method and their structural and transport properties were measured. All obtained samples crystallize in hexagonal R-3c perovskite structure. The thermal stability was found to decrease with increasing Ni and Sr amounts, what leads to appearance of La2NiO4 like secondary phases with spinel structure and even NiO for higher Ni concentration. The DC electrical conductivity and thermoelectric power measurements at low temperatures (77 – 300K) suggest an appearance of variable hopping mechanism in this
temperature range. The transport properties were found to improve with both Sr and Ni concentration increases. The moessbauer spectroscopy studies of La1-xSrxCo0.2Fe0.6Ni0.2O3-d samples revealed presence of two valence states of iron (Fe2+, Fe3+). The measured high temperature (870 – 1070K) DC electrical conductivity is relatively high for samples with high Sr and Ni amounts, what makes them good candidates for a possible application as cathode materials for Intermediate Temperature Solid Oxide Fuel Cells and points to further studies of
perovskites from the (La, Sr)(Co, Fe, Ni)O3 system.