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.

Zinc Self-Diffusion in ZnO

2005 ◽  
Vol 237-240 ◽  
pp. 163-168 ◽  
Author(s):  
M.A.N. Nogueira ◽  
Antônio Claret Soares Sabioni ◽  
Wilmar Barbosa Ferraz
Keyword(s):  
Diffusion Coefficient ◽  
Grain Boundary ◽  
Diffusion Coefficients ◽  
Boundary Diffusion ◽  
Volume Diffusion ◽  
Grain Boundary Diffusion ◽  
Polished Surface ◽  
Self Diffusion ◽  
Zinc Diffusion ◽  
Diffusion Profiles

This work deals with the study of zinc self-diffusion in ZnO polycrystal of high density and of high purity. The diffusion experiments were performed using the 65Zn radioactive isotope as zinc tracer. A thin film of the tracer was deposited on the polished surface of the samples, and then the diffusion annealings were performed from 1006 to 1377oC, in oxygen atmosphere. After the diffusion treatment, the 65Zn diffusion profiles were established by means of the Residual Activity Method. From the zinc diffusion profiles were deduced the volume diffusion coefficient and the product dDgb for the grain-boundary diffusion, where d is the grain-boundary width and Dgb is the grain-boundary diffusion coefficient. The results obtained for the volume diffusion coefficient show good agreement with the most recent results obtained in ZnO single crystals using stable tracer and depth profiling by secondary ion mass spectrometry, while for the grain-boundary diffusion there is no data published by other authors for comparison with our results. The zinc grain-boundary diffusion coefficients are ca. 4 orders of magnitude greater than the volume diffusion coefficients, in the same experimental conditions, which means that grain-boundary is a fast path for zinc diffusion in polycrystalline ZnO.

Measurement of growth rates for single crystals and pressed tablets of CuSO4.5 H2O on a rotating disc

1989 ◽  
Vol 54 (11) ◽  
pp. 2951-2961 ◽  
Author(s):  
Miloslav Karel ◽  
Jaroslav Nývlt
Keyword(s):  
Growth Rate ◽  
Single Crystal ◽  
Single Crystals ◽  
Growth Rates ◽  
Diffusion Coefficients ◽  
Preferred Orientation ◽  
Rotating Disc ◽  
Dissolution Rates ◽  
Rates Of Growth ◽  
Good Agreement

Measured growth and dissolution rates of single crystals and tablets were used to calculate the overall linear rates of growth and dissolution of CuSO4.5 H2O crystals. The growth rate for the tablet is by 20% higher than that calculated for the single crystal. It has been concluded that this difference is due to a preferred orientation of crystal faces on the tablet surface. Calculated diffusion coefficients and thicknesses of the diffusion and hydrodynamic layers in the vicinity of the growing or dissolving crystal are in good agreement with published values.

scholarly journals Effect of Modification on the Fluid Diffusion Coefficient in Silica Nanochannels

Molecules ◽  
2021 ◽  
Vol 26 (13) ◽  
pp. 4030
Author(s):  
Gengbiao Chen ◽  
Zhiwen Liu
Keyword(s):  
Diffusion Coefficient ◽  
Diffusion Coefficients ◽  
Surface Effect ◽  
Bulk Water ◽  
Self Diffusion ◽  
Average Diffusion Coefficient ◽  
Average Diffusion ◽  
Chain Lengths ◽  
Fluid Diffusion ◽  
Self Diffusion Coefficient

The diffusion behavior of fluid water in nanochannels with hydroxylation of silica gel and silanization of different modified chain lengths was simulated by the equilibrium molecular dynamics method. The diffusion coefficient of fluid water was calculated by the Einstein method and the Green–Kubo method, so as to analyze the change rule between the modification degree of nanochannels and the diffusion coefficient of fluid water. The results showed that the diffusion coefficient of fluid water increased with the length of the modified chain. The average diffusion coefficient of fluid water in the hydroxylated nanochannels was 8.01% of the bulk water diffusion coefficient, and the diffusion coefficients of fluid water in the –(CH2)3CH3, –(CH2)7CH3, and –(CH2)11CH3 nanochannels were 44.10%, 49.72%, and 53.80% of the diffusion coefficients of bulk water, respectively. In the above four wall characteristic models, the diffusion coefficients in the z direction were smaller than those in the other directions. However, with an increase in the silylation degree, the increased self-diffusion coefficient due to the surface effect could basically offset the decreased self-diffusion coefficient owing to the scale effect. In the four nanochannels, when the local diffusion coefficient of fluid water was in the range of 8 Å close to the wall, Dz was greater than Dxy, and beyond the range of 8 Å of the wall, the Dz was smaller than Dxy.

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.

Self-Diffusion in Molten Lithium Nitrate

1992 ◽  
Vol 47 (10) ◽  
pp. 1047-1050 ◽  
Author(s):  
C. Herdlicka ◽  
J. Richter ◽  
M. D. Zeidler
Keyword(s):  
Diffusion Coefficient ◽  
Diffusion Coefficients ◽  
Spin Echo ◽  
The Self ◽  
Lithium Nitrate ◽  
Equimolar Ratio ◽  
Self Diffusion ◽  
Field Gradients ◽  
Molten Lithium ◽  
Self Diffusion Coefficient

AbstractSelf-diffusion coefficients of 7Li+ ions have been measured in molten LiNO3 with several compositions of 6Li+ and 7Li+ over a temperature range from 537 to 615 K. The NMR spin-echo method with pulsed field gradients was applied. It was found that the self-diffusion coefficient depends on the isotopic composition and shows a maximum at equimolar ratio. At temperatures above 600 K this behaviour disappears.

scholarly journals Diffusional Properties of Methanogenic Granular Sludge: 1H NMR Characterization

2003 ◽  
Vol 69 (11) ◽  
pp. 6644-6649 ◽  
Author(s):  
Piet N. L. Lens ◽  
Rakel Gastesi ◽  
Frank Vergeldt ◽  
Adriaan C. van Aelst ◽  
Antonio G. Pisabarro ◽  
...  
Keyword(s):  
Diffusion Coefficient ◽  
Relaxation Time ◽  
Nmr Spectroscopy ◽  
Diffusion Coefficients ◽  
Metal Sulfide ◽  
Free Water ◽  
Granular Sludge ◽  
Self Diffusion ◽  
Nmr Characterization ◽  
Self Diffusion Coefficient

ABSTRACT The diffusive properties of anaerobic methanogenic and sulfidogenic aggregates present in wastewater treatment bioreactors were studied using diffusion analysis by relaxation time-separated pulsed-field gradient nuclear magnetic resonance (NMR) spectroscopy and NMR imaging. NMR spectroscopy measurements were performed at 22°C with 10 ml of granular sludge at a magnetic field strength of 0.5 T (20 MHz resonance frequency for protons). Self-diffusion coefficients of H2O in the investigated series of mesophilic aggregates were found to be 51 to 78% lower than the self-diffusion coefficient of free water. Interestingly, self-diffusion coefficients of H2O were independent of the aggregate size for the size fractions investigated. Diffusional transport occurred faster in aggregates growing under nutrient-rich conditions (e.g., the bottom of a reactor) or at high (55°C) temperatures than in aggregates cultivated in nutrient-poor conditions or at low (10°C) temperatures. Exposure of aggregates to 2.5% glutaraldehyde or heat (70 or 90°C for 30 min) modified the diffusional transport up to 20%. In contrast, deactivation of aggregates by HgCl2 did not affect the H2O self-diffusion coefficient in aggregates. Analysis of NMR images of a single aggregate shows that methanogenic aggregates possess a spin-spin relaxation time and self-diffusion coefficient distribution, which are due to both physical (porosity) and chemical (metal sulfide precipitates) factors.

Self-diffusion in gold single crystals at low temperatures

1968 ◽  
Vol 46 (23) ◽  
pp. 2589-2594 ◽  
Author(s):  
J. L. Whitton ◽  
G. V. Kidson
Keyword(s):  
Single Crystals ◽  
Diffusion Coefficients ◽  
Low Temperatures ◽  
Bulk Diffusion ◽  
Lattice Diffusion ◽  
Fast Diffusion ◽  
Initial Portion ◽  
Self Diffusion ◽  
Normal Lattice ◽  
Structure Sensitive

Self-diffusion in gold single crystals has been studied at temperatures between 335 to 390 °C for times between 15 and 30 min. The concentration profiles, obtained by use of a sensitive sectioning technique, consist of a region that appears to be characteristic of bulk diffusion, followed by a deeply penetrating 'tail' that is structure sensitive. Diffusion coefficients extracted from the initial portion of the curves are somewhat larger than those predicted from an extrapolation of high temperature measurements. The results are interpreted in terms of a combination of normal lattice diffusion and fast diffusion along dislocations.

Dislocation-enhanced diffusion in silver single crystals

1970 ◽  
Vol 48 (13) ◽  
pp. 1548-1552 ◽  
Author(s):  
C. T. Lai ◽  
H. M. Morrison
Keyword(s):  
Crystal Lattice ◽  
Single Crystals ◽  
Diffusion Coefficients ◽  
Enhanced Diffusion ◽  
Temperature Range ◽  
Self Diffusion

An electrolytic sectioning technique has been used to measure self-diffusion coefficients in silver single crystals in the temperature range 300–800 °C. The results are analyzed in terms of diffusion through the crystal lattice, enhanced by diffusion along dislocations.

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