Self- and Solute Diffusion, Interdiffusion and Thermal Vacancies in the System Iron-Aluminium

2013 ◽  
Vol 333 ◽  
pp. 1-25 ◽  
Author(s):  
Helmut Mehrer ◽  
Martin Luckabauer ◽  
Wolfgang Sprengel
Keyword(s):  
Positron Annihilation ◽  
Experimental Studies ◽  
Tracer Diffusion ◽  
Al Alloys ◽  
Solute Diffusion ◽  
Diffusion Studies ◽  
High Fraction ◽  
Diffusion Mechanisms ◽  
Interdiffusion Coefficients ◽  
And Diffusion

Starting from fundamental aspects of thermal vacancies and solid-state self-and solute diffusion, this paper reviews procedures for tracer-and interdiffusion studies and of the major techniques for vacancy studies by dilatometry and positron annihilation in metals. Equilibrium vacancy and diffusion studies performed on pure iron and aluminium are mentioned at first. We also comment some peculiarities of solute diffusion in aluminium. Positron annihilation and differential dilatometry studies for Fe-Al alloys with various compositions are summarized and new experimental studies by the authors are reported for vacancy migration in Fe61Al39. All these studies indicate a relatively high fraction of thermal vacancies with relatively low mobility in this type of iron-aluminides as compared to pure metals. Tracer diffusion of iron and of several substitutional solutes such as Co, Ni, Cr, Mn, Zn, and In in Fe-Al from the Münster laboratory are summarized. The diffusion studies of Fe-Al cover various alloy composition between Fe3Al and FeAl and several structures such as A2, B2 and D03. Interdiffusion coefficients obtained from diffusion couples between Fe-Al alloys are discussed together with Fe tracer diffusion data. The Darken-Manning equation is used to deduce Al diffusivities therefrom. The latter are hardly accessible to radiotracer experiments due to a lack of a suitable Al tracer. Diffusion of Al is slightly faster than diffusion of Fe indicating diffusion mechanisms with coupled jumps of Fe and Al atoms.

Site Preference and Diffusion in Ni3Al Alloyed with Ir, Ta or Re at 1200°C

2010 ◽  
Vol 297-301 ◽  
pp. 1322-1327 ◽  
Author(s):  
N. Garimella ◽  
H.J. Choi ◽  
Yong Ho Sohn
Keyword(s):  
Diffusion Coefficients ◽  
Tracer Diffusion ◽  
Site Preference ◽  
Solid Diffusion ◽  
Ordered Intermetallic ◽  
Ternary Alloying ◽  
Tracer Diffusion Coefficients ◽  
Interdiffusion Coefficients ◽  
And Diffusion

Diffusion in L12-Ni3Al with ternary alloying additions of Ir, Ta and Re was investigated at 1200°C using solid-to-solid diffusion couples, and examined with respect to site preference in ordered intermetallic compound. In addition to determination of average ternary interdiffusion coefficients [1-3], average effective interdiffusion coefficients were determined directly from the experimental concentration profiles. Ni has the largest magnitude of average effective interdiffusion coefficient, followed by Al, Ir, Re and Ta. The average effective interdiffusion coefficients for Ir, Re and Ta are much smaller than those for Ni and Al. Tracer diffusion coefficients determined by extrapolation technique, and available literature also followed the same trend. The relative tendency of Ni, Al, Ir, Re and Ta to occupy the -Ni and -Al sites are correlated to these diffusion coefficients, with due consideration for diffusion mechanisms and coordination of atoms.

Li-Defect Reactions During Low Dose Ion Implantation of 8LI into ZNSE Single Crystals

1998 ◽  
Vol 540 ◽  
Author(s):  
M. Restle ◽  
M. Dalmer ◽  
U. Wahl ◽  
H. Hofsäss
Keyword(s):  
Single Crystals ◽  
Lattice Site ◽  
Low Dose ◽  
Vacancy Concentration ◽  
Site Location ◽  
Recombination Processes ◽  
Diffusion Studies ◽  
Defect Reactions ◽  
High Fraction ◽  
And Diffusion

AbstractWe present lattice site location and diffusion studies of ion implanted 8Li in ZnSe single crystals at sample temperatures between 180 K and 550 K using the emission channeling technique. Below 200 K, Li is immobile in ZnSe and occupies tetrahedral interstitial sites. Above 250 K, interstitial Li becomes mobile and for an accumulated dose above 1×1012 cm-2 the majority of the implanted Li atoms occupy substitutional sites, presumably Zn sites. However, for room temperature implantation at doses below 1×1012 cm-2, the majority of implanted Li still occupies interstitial sites. This behavior is explained by recombination processes between Zn interstitials and vacancies, thus reducing the vacancy concentration and maintaining a high fraction of interstitial Li. Substitutional Li is stable up to about 500 K and diffuses out for temperatures above. We calculate 0.5 eV for the migration energy of interstitial Li and 1.38 eV for the binding energy of substitutional Li.

scholarly journals A Simulation Study of Alkanes in Linde Type A Zeolites

2007 ◽  
Vol 25 (6) ◽  
pp. 417-427 ◽  
Author(s):  
Almudena García-Sánchez ◽  
Elena García-Pérez ◽  
David Dubbeldam ◽  
Rajamani Krishna ◽  
Sofía Calero
Keyword(s):  
Experimental Studies ◽  
Type A ◽  
Self Diffusion ◽  
Linear Alkanes ◽  
Diffusion Studies ◽  
Zeolite Type ◽  
5A Zeolite ◽  
Lower Mobility ◽  
And Diffusion ◽  
Molecular Picture

Monte Carlo simulations were performed to study the adsorption and diffusion of small hydrocarbons in Linde Type A zeolites as a function of their calcium/sodium ratio. The diffusion studies were focused on methane whereas the adsorption simulations were performed from methane up to pentane. The results obtained showed that an increase in the number of cations in the structure (exchange of univalent sodium ions by divalent calcium ions) led to an increase in the adsorption of linear alkanes at low and medium pressure, but caused a decrease in adsorption at the highest pressures. An increase in the amount of cations favours molecular attraction and hence results in lower mobility. At higher cation loading the ions block the windows interconnecting the LTA cages, leading to a further decrease in diffusion. Methane self-diffusion coefficients obtained from our simulations were twice as high for the Linde Type 5A zeolite as for the Linde Type 4A zeolite. These results are consistent with previous experimental studies and provide a molecular picture of the influence of the zeolite type, the amount of cations contained and their location in the structure.

Non-Stoichiometry and Cation Tracer Diffusion Studies in the Magnetite-UlvÖSpinel Solution, (Fe,Ti)3-δO4

1994 ◽  
Vol 369 ◽  
Author(s):  
Sanjeev Aggarwal ◽  
Rudiger Dieckmann
Keyword(s):  
Diffusion Coefficients ◽  
Tracer Diffusion ◽  
Oxygen Activity ◽  
Spinel Solid Solution ◽  
Low Oxygen ◽  
Cation Diffusion ◽  
Deviation From Stoichiometry ◽  
Diffusion Studies ◽  
Tracer Diffusion Coefficients ◽  
Point Defect Structure

AbstractCation diffusion in the spinel solid solution (Fe1-xTix)3-δO4 (0≤ x ≤ 0.3) was investigated at 1200 ºC as a function of oxygen activity, aO2 and cationic composition, x. At different cationic compositions, cation tracer diffusion coefficients, D*Me of Me = Fe and Ti were measured as a function of oxygen activity. Plots of log DMe vs. loga0 show V-shaped curves, indicating that different types of point defects prevail at high anc low oxygen activities. Thermogravimetric experiments were conducted, using a high resolution microbalance, to determine the deviation from stoichiometry in (Fe1-xTix)3-δO4 at 1200 °C. δversus log aO2 curves are S-shaped. An analysis of the oxygen activity dependences of thecation diffusion coefficients and the deviation from stoichiometry with regardto the point defect structure suggests that at high oxygen activities cation vacancies are the predominant defects governing the deviation from stoichiometry and the diffusion ofcations. At low oxygen activities, and at small values of x, cation interstitials determine the deviation from stoichiometry, while they dominate for 0 ≤ x ≤ 0.3 inthe cation diffusion.

Gold implantation inn‐type silicon: Entropy factor and diffusion studies

1990 ◽  
Vol 68 (4) ◽  
pp. 1601-1605 ◽  
Author(s):  
S. Coffa ◽  
L. Calcagno ◽  
G. Ferla ◽  
S. U. Campisano
Keyword(s):  
Type Silicon ◽  
Diffusion Studies ◽  
Entropy Factor ◽  
And Diffusion

Pollution plume transport and diffusion studies using fluorescence lidar

1980 ◽  
Vol 19 (15) ◽  
pp. 2524 ◽  
Author(s):  
Burton G. Schuster ◽  
Thomas G. Kyle
Keyword(s):  
Diffusion Studies ◽  
Transport And Diffusion ◽  
Plume Transport ◽  
And Diffusion

scholarly journals Structural and Functional Regulation of Tight Junctions by RhoA and Rac1 Small GTPases

1998 ◽  
Vol 142 (1) ◽  
pp. 101-115 ◽  
Author(s):  
Tzuu-Shuh Jou ◽  
Eveline E. Schneeberger ◽  
W. James Nelson
Keyword(s):  
Tight Junctions ◽  
Spatial Organization ◽  
Mdck Cells ◽  
Protein Localization ◽  
Freeze Fracture ◽  
Tracer Diffusion ◽  
Small Gtpases ◽  
Dominant Negative ◽  
Solute Diffusion ◽  
Fence Function

Tight junctions (TJ) govern ion and solute diffusion through the paracellular space (gate function), and restrict mixing of membrane proteins and lipids between membrane domains (fence function) of polarized epithelial cells. We examined roles of the RhoA and Rac1 GTPases in regulating TJ structure and function in MDCK cells using the tetracycline repressible transactivator to regulate RhoAV14, RhoAN19, Rac1V12, and Rac1N17 expression. Both constitutively active and dominant negative RhoA or Rac1 perturbed TJ gate function (transepithelial electrical resistance, tracer diffusion) in a dose-dependent and reversible manner. Freeze-fracture EM and immunofluoresence microscopy revealed abnormal TJ strand morphology and protein (occludin, ZO-1) localization in RhoAV14 and Rac1V12 cells. However, TJ strand morphology and protein localization appeared normal in RhoAN19 and Rac1N17 cells. All mutant GTPases disrupted the fence function of the TJ (interdomain diffusion of a fluorescent lipid), but targeting and organization of a membrane protein in the apical membrane were unaffected. Expression levels and protein complexes of occludin and ZO-1 appeared normal in all mutant cells, although ZO-1 was more readily solubilized from RhoAV14-expressing cells with Triton X-100. These results show that RhoA and Rac1 regulate gate and fence functions of the TJ, and play a role in the spatial organization of TJ proteins at the apex of the lateral membrane.

ULTRACENTRIFUGE AND DIFFUSION STUDIES ON GLUTEN

1942 ◽  
Vol 20c (3) ◽  
pp. 130-159 ◽  
Author(s):  
A. G. McCalla ◽  
Nils Gralén
Keyword(s):  
Sodium Salicylate ◽  
Minimum Weight ◽  
Average Molecular Weight ◽  
Sedimentation Equilibrium ◽  
Velocity Sedimentation ◽  
Molecular Characteristics ◽  
Weight Average Molecular Weight ◽  
Diffusion Constants ◽  
Diffusion Studies ◽  
And Diffusion

The molecular characteristics of gluten in sodium salicylate solutions were studied by means of sedimentation velocity, sedimentation equilibrium, and diffusion measurements. The proportion of total gluten protein molecularly dispersed increased with increase in concentration of sodium salicylate up to 12%, but the dispersed portions had essentially the same sedimentation constant (2.5 ± 0.15) regardless of the concentration of the dispersing medium.The most soluble 25 per cent of the gluten was all molecularly dispersed, but was definitely inhomogeneous. The weight-average molecular weight of this fraction was 44,000, but there is reason to believe the minimum weight may be about 35,000. None of the other fractions was entirely molecularly dispersed, the proportion decreasing with decreasing solubility of the fractions. Aggregates of many sizes existed in all of these fractions, but only the most insoluble contained aggregates large enough to cause opacity. Sedimentation constants of the molecularly dispersed portions increased slightly with decreasing solubility, while diffusion constants decreased markedly. None of the fractions yielded normal curves (diffusion diagrams) but the more soluble the fraction, the more nearly normal the curve. The inhomogeneity responsible for the varying rates of diffusion was due partly to differences in proportion and properties of the molecularly dispersed gluten and partly to aggregates.All properties showed progressive changes both within and between the arbitrarily produced fractions. These results, therefore, support the hypothesis that gluten is a protein system showing progressive and regular changes in properties with change in solubility.

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