Diffusion of Zinc in Two-Phase Mg-Al Alloy

2007 ◽  
Vol 263 ◽  
pp. 189-194
Author(s):  
Ivo Stloukal ◽  
Jiří Čermák
Keyword(s):  
Diffusion Coefficient ◽  
Diffusion Coefficients ◽  
Effective Diffusion ◽  
Residual Activity ◽  
Diffusion Path ◽  
Al Alloy ◽  
Serial Sectioning ◽  
Two Phase ◽  
Interphase Boundaries ◽  
The Mean

Coefficient of 65Zn heterodiffusion in Mg17Al12 intermetallic and in eutectic alloy Mg - 33.4 wt. % Al was measured in the temperature region 598 – 698 K using serial sectioning and residual activity methods. Diffusion coefficient of 65Zn in the intermetallic can be written as DI = 1.7 × 10-2 m2 s-1 exp (-155.0 kJ mol-1 / RT). At temperatures T ≥ 648 K, where the mean diffusion path was greater than the mean interlamellar distance in the eutectic, the effective diffusion coefficient Def = 2.7 × 10-2 m2 s-1 exp (-155.1 kJ mol-1 / RT) was evaluated. At two lower temperatures, the diffusion coefficients 65Zn in interphase boundaries were estimated: Db (623 K) = 1.6 × 10-12 m2 s-1 and Db (598 K) = 4.4 × 10-13 m2 s-1.

scholarly journals Specific features of eddy turbulence in the turbopause region

2014 ◽  
Vol 32 (4) ◽  
pp. 431-442 ◽  
Author(s):  
M. N. Vlasov ◽  
M. C. Kelley
Keyword(s):  
Diffusion Coefficient ◽  
Heat Transport ◽  
Diffusion Coefficients ◽  
Transport Coefficient ◽  
Molecular Diffusion ◽  
Eddy Diffusion ◽  
Cooling Rates ◽  
Eddy Diffusion Coefficient ◽  
Eddy Heat Transport ◽  
The Mean

Abstract. The turbopause region is characterized by transition from the mean molecular mass (constant with altitude) to the mean mass (dependent on altitude). The former is provided by eddy turbulence, and the latter is induced by molecular diffusion. Competition between these processes provides the transition from the homosphere to the heterosphere. The turbopause altitude can be defined by equalizing the eddy and molecular diffusion coefficients and can be located in the upper mesosphere or the lower thermosphere. The height distributions of chemical inert gases very clearly demonstrate the transition from turbulent mixing to the diffusive separation of these gases. Using the height distributions of the chemical inert constituents He, Ar, and N2 given by the MSIS-E-90 model and the continuity equations, the height distribution of the eddy diffusion coefficient in the turbopause region can be inferred. The eddy diffusion coefficient always strongly reduces in the turbopause region. According to our results, eddy turbulence above its peak always cools the atmosphere. However, the cooling rates calculated with the eddy heat transport coefficient equaled to the eddy diffusion coefficient were found to be much larger than the cooling rates corresponding to the neutral temperatures given by the MSIS-E-90 model. The same results were obtained for the eddy diffusion coefficients inferred from different experimental data. The main cause of this large cooling is the very steep negative gradient of the eddy heat transport coefficient, which is equal to the eddy diffusion coefficient if uniform turbulence takes place in the turbopause region. Analysis of wind shear shows that localized turbulence can develop in the turbopause region. In this case, eddy heat transport is not so effective and the strong discrepancy between cooling induced by eddy turbulence and cooling corresponding to the temperature given by the MSIS-E-90 model can be removed.

scholarly journals Field Validation of Concrete Transport Property Measurement Methods

Materials ◽  
2020 ◽  
Vol 13 (5) ◽  
pp. 1166 ◽  
Author(s):  
Ahmed Abd El Fattah ◽  
Ibrahim Al-Duais ◽  
Kyle Riding ◽  
Michael Thomas ◽  
Salah Al-Dulaijan ◽  
...  
Keyword(s):  
Diffusion Coefficient ◽  
Diffusion Coefficients ◽  
Effective Diffusion Coefficient ◽  
Corrosion Inhibitors ◽  
Effective Diffusion ◽  
Cementitious Materials ◽  
Supplementary Cementitious Materials ◽  
Chloride Diffusion ◽  
Chloride Ingress ◽  
Exposure Site

Reinforcing steel corrosion, caused by chloride ingress into concrete, is the leading cause of reinforced concrete deterioration. One of the main findings in the literature for reducing chloride ingress is the improvement of the durability characteristics of concrete by the addition of supplementary cementitious materials (SCMs) and/or chemical agents to concrete mixtures. In this study, standard ASTM tests—such as rapid chloride permeability (RCPT), bulk diffusion and sorptivity tests—were used to measure concrete properties such as porosity, sorptivity, salt diffusion, and permeability. Eight different mixtures, prepared with different SCMs and corrosion inhibitors, were tested. Apparent and effective chloride diffusion coefficients were calculated using bound chloride isotherms and time-dependent decrease in diffusion. Diffusion coefficients decreased with time, especially with the addition of SCMs and corrosion inhibitors. The apparent diffusion coefficient calculated using the error function was slightly lower than the effective diffusion coefficient; however, there was a linear trend between the two. The formation factor was found to correlate with the effective diffusion coefficient. The results of the laboratory tests were compared and benchmarked to their counterparts in the marine exposure site in the Arabian Gulf in order to identify laboratory key tests to predict concrete durability. The overall performance of concrete containing SCMs, especially fly ash, were the best among the other mixtures in the laboratory and the field.

Diffusion velocity lattice Boltzmann formulation applied to transport in macroscopic porous media

2014 ◽  
Vol 25 (12) ◽  
pp. 1441006 ◽  
Author(s):  
Janez Perko ◽  
Ravi A. Patel
Keyword(s):  
Porous Media ◽  
Diffusion Coefficient ◽  
Lattice Boltzmann ◽  
Diffusion Coefficients ◽  
Effective Diffusion ◽  
Hydrodynamic Dispersion ◽  
Traditional Treatment ◽  
Dissipative Term ◽  
Diffusion Velocity ◽  
Variable Diffusion

This paper describes the application of a single relaxation time (SRT) lattice Boltzmann scheme to the transport in porous media with large spatial variations of diffusion coefficients. Effective diffusion coefficients can vary substantially within porous media because of their dependence on porosity and tortuosity which can span over several orders of magnitude, depending on pore size and connectivity. Moreover, when mass is transported with pore-water in porous media, the hydrodynamic dispersion, which depends on Darcy's velocity, contributes additionally to the usually anisotropic variation of the dissipative term. In contrast to the traditional treatment of spatially variable diffusion coefficient by the variation of a SRT, here the variability is accommodated through the use of diffusion velocity formulation which allows for larger variabilities of diffusion coefficient. The volume averaged properties of mass transport in macroscopic porous media are resolved through the additional source term which is similar to the existing force adjusting methods. The applicability of both the proposed schemes is demonstrated on two examples. The first demonstrates that the method is accurate for the large variation of diffusion coefficients and porosities. The second example introduces mass diffusion in a real, geometrically complex system with spatially contrasting properties.

scholarly journals Crowding and Confinement Effects on Protein Diffusion In Vivo

2006 ◽  
Vol 188 (17) ◽  
pp. 6115-6123 ◽  
Author(s):  
Michael C. Konopka ◽  
Irina A. Shkel ◽  
Scott Cayley ◽  
M. Thomas Record ◽  
James C. Weisshaar
Keyword(s):  
Diffusion Coefficient ◽  
Fluorescent Protein ◽  
Volume Fraction ◽  
Effective Diffusion ◽  
Relative Dispersion ◽  
Protein Diffusion ◽  
Confinement Effects ◽  
The Mean

ABSTRACT The first in vivo measurements of a protein diffusion coefficient versus cytoplasmic biopolymer volume fraction are presented. Fluorescence recovery after photobleaching yields the effective diffusion coefficient on a 1-μm-length scale of green fluorescent protein within the cytoplasm of Escherichia coli grown in rich medium. Resuspension into hyperosmotic buffer lacking K+ and nutrients extracts cytoplasmic water, systematically increasing mean biopolymer volume fraction, <φ>, and thus the severity of possible crowding, binding, and confinement effects. For resuspension in isosmotic buffer (osmotic upshift, or Δ, of 0), the mean diffusion coefficient, <D>, in cytoplasm (6.1 ± 2.4 μm2 s−1) is only 0.07 of the in vitro value (87 μm2 s−1); the relative dispersion among cells, σ D /<D> (standard deviation, σ D , relative to the mean), is 0.39. Both <D> and σ D /<D> remain remarkably constant over the range of Δ values of 0 to 0.28 osmolal. For a Δ value of ≥0.28 osmolal, formation of visible plasmolysis spaces (VPSs) coincides with the onset of a rapid decrease in <D> by a factor of 380 over the range of Δ values of 0.28 to 0.70 osmolal and a substantial increase in σ D /<D>. Individual values of D vary by a factor of 9 × 104 but correlate well with f VPS, the fractional change in cytoplasmic volume on VPS formation. The analysis reveals two levels of dispersion in D among cells: moderate dispersion at low Δ values for cells lacking a VPS, perhaps related to variation in φ or biopolymer organization during the cell cycle, and stronger dispersion at high Δ values related to variation in f VPS. Crowding effects alone cannot explain the data, nor do these data alone distinguish crowding from possible binding or confinement effects within a cytoplasmic meshwork.

scholarly journals Impact of Pore Geometry and Water Saturation on Gas Effective Diffusion Coefficient in Soil

2018 ◽  
Vol 8 (11) ◽  
pp. 2097 ◽  
Author(s):  
Wulong Hu ◽  
Yao Jiang ◽  
Daoyi Chen ◽  
Yongshui Lin ◽  
Qiang Han ◽  
...  
Keyword(s):  
Diffusion Coefficient ◽  
Power Law ◽  
Diffusion Coefficients ◽  
Effective Diffusion Coefficient ◽  
Pore Diameter ◽  
Water Saturation ◽  
Knudsen Diffusion ◽  
Effective Diffusion ◽  
Pore Geometry ◽  
Effective Diffusion Coefficients

Gas flow in soil plays a crucial role in terrestrial ecosystems, and numerical simulation of their movement needs to know their effective diffusion coefficients. How pore structure influences the effective diffusion coefficient has been studied intensively for dry porous media, but much remains unknown for unsaturated soils. Here, we employed the X-ray tomography technique at the pore scale to directly obtain the soil structures, the geometry of their pores and the water distribution under different water saturation levels were calculated using a morphological model. The results show that pore structures including porosity, interface area of gas–solid–water and pore diameter are closely related to water saturation. The increase of mean pore diameter with gas saturation can be fitted into a power law. We also investigated the impact of pore geometry and water saturation on the effective diffusion coefficients, which is independent of the molecular mass of gas after normalization. As the normalized effective Knudsen diffusion coefficient increases with average pore diameter following a power law, with the scaling factor related to pore geometry and the exponent is a constant, we explained and proved that the Knudsen diffusion coefficient increases with gas saturation, also following a power law.

scholarly journals Unbiased Diffusion through a Linear Porous Media with Periodic Entropy Barriers: A Tube Formed by Contacting Ellipses

2015 ◽  
Vol 2015 ◽  
pp. 1-10 ◽  
Author(s):  
Yoshua Chávez ◽  
Marco-Vinicio Vázquez ◽  
Leonardo Dagdug
Keyword(s):  
Diffusion Coefficient ◽  
Cross Section ◽  
Effective Diffusion Coefficient ◽  
Effective Diffusion ◽  
Radial Symmetry ◽  
Computational Simulations ◽  
One Dimensional ◽  
Brownian Particles ◽  
Mathematical Expressions ◽  
The Mean

This work is devoted to the study of unbiased diffusion of point-like Brownian particles through channels with radial symmetry of varying cross-section and elliptic shape. The effective one-dimensional reduction is used with distinct forms of a position-dependent diffusion coefficient,D(x), found in literature, to obtain expressions for (I) narrow escape times from a single open-ended tube, (II) its correspondent effective diffusion coefficient, both as functions of the eccentricity of the tube,ε, whereε= 0 returns the system to a spherical vesicle with two open opposite sides, and (III) finally, Lifson-Jackson formula that is used to compute expressions to assess the mean effective diffusion coefficient for a periodic elliptic channel formed by contacting ellipses, also as a function of the eccentricity. Mathematical expressions are presented and contrasted against computational simulations to validate them.

scholarly journals Diffusion Coefficients from the Rate of Decay of Meteor Trails

1955 ◽  
Vol 8 (2) ◽  
pp. 279 ◽  
Author(s):  
AA Weiss
Keyword(s):  
Diffusion Coefficient ◽  
Diffusion Coefficients ◽  
Effective Diffusion Coefficient ◽  
Effective Diffusion ◽  
Upper Atmosphere ◽  
Absolute Value ◽  
Meteor Trail ◽  
Rate Of Decay ◽  
Meteor Trails ◽  
Rates Of Decay

The effective diffusion coefficient for a meteor trail is calculated from the theory of ambipolar diffusion and the physical constants of the upper atmosphere. The absolute value of the diffusion coefficient so calculated, and also its gradient with height, are confirmed by measurement of the rates of decay of a large number of meteor echoes of known heights.

The Measurement of Diffusion Coefficient Using Nanofluidic Channels

2007 ◽  
Author(s):  
Steve Rhieu ◽  
David Huber ◽  
Marci Markel ◽  
G. Tayhas R. Palmore ◽  
Sumita Pennathur
Keyword(s):  
Diffusion Coefficient ◽  
Diffusion Coefficients ◽  
Peclet Number ◽  
Transport Theory ◽  
Effective Diffusion ◽  
Least Square ◽  
Sodium Fluorescein ◽  
Complex Species ◽  
Péclet Number ◽  
Nanofluidic Channels

The behavior of molecules confined within nanochannels may provide new insight into important chemical and biological mechanisms. As such, the ability to measure the diffusion coefficient of molecules accurately and rapidly is critical. Toward this end, we demonstrate a new method for measuring the diffusion coefficient of analytes in nanoscale environments. Based on nanoscale electrokinetic transport theory, a numerical simulation was developed to determine the spatial concentration of analyte within a nanofluidic T-shaped channel for a given Peclet number. The resulting concentration profiles were compared to experimental data to determine the Peclet number that gives the minimum least-square error. Using this approach, the diffusion coefficient of sodium fluorescein was measured and found to be within the error of previously published values. This method is envisioned to be a novel analytical tool to rapidly and accurately measure diffusion coefficients of small analytes, and to measure the effective diffusion coefficients of more complex species such as DNA and peptides when confined within a nanochannel.

Interphase Boundary Diffusion in Eutectic Alloys

1985 ◽  
Vol 57 ◽  
Author(s):  
G. A. Chadwick
Keyword(s):  
Diffusion Coefficient ◽  
Single Crystal ◽  
Single Crystals ◽  
Interphase Boundary ◽  
Diffusion Coefficients ◽  
Noble Metals ◽  
Boundary Diffusion ◽  
Eutectic Alloys ◽  
Self Diffusion ◽  
Interphase Boundaries

AbstractTurnbull and co-workers have shown that the noble metals Cu, Ag, and Au diffuse into single crystals of Pb and Sn by an interstitialcy mechanism with measured diffusion coefficients of ∼10−6cm2s−1. These experiments have been extended to study the diffusion rates of the noble metals along the interphase boundaries of single crystal of Pb-Sn eutectic alloys and to measure the diffusion coefficient of silver along the interphase boundaries of Ag-Cu eutectic single crystals.The measured interphase boundary diffusion coefficients of the noble metals in the Pb-Sn single crystals are extremely high, being 2.6 × 10−3cm2s−1for Cu and ∼10−4cm2s−1for Ag and Au at room temperature. These results again imply an interstitialcy mechanism of diffusion at the interphase boundaries. In contrast, the diffusion coefficient of Ag110in a Ag-Cu eutectic single crystal worked out to be ∼8×10−9cm2s−1at 500°C, two orders of magnitude lower than the value obtained by Turnbull and Hoffman for self-diffusion along low-angle (8∼10°) boundaries in silver.

Sign in / Sign up

Export Citation Format

Share Document