A Simulation Study of Tracer Diffusion Concentration Profiles Resulting from the Transition from Dislocation Pipes to a Grain Boundary Slab

2001 ◽  
Vol 677 ◽  
Author(s):  
Irina V Belova ◽  
Graeme E Murch
Keyword(s):  
Grain Boundary ◽  
Diffusion Length ◽  
Grid Method ◽  
Tracer Diffusion ◽  
Concentration Profiles ◽  
Tracer Concentration ◽  
Type Analysis ◽  
Concentration Depth Profile ◽  
Dislocation Pipe ◽  
Lattice Diffusivity

ABSTRACTIn the present study we examine the well-known analysis in which the dislocation pipe diffusivity is determined by means of a grain boundary type analysis of the tail of a tracer concentration depth profile. We use a Monte Carlo grid method for testing the analysis. The results show that the analysis is really only satisfactory when the spacing between the dislocations is roughly twice the diffusion length (Dlt)½ where Dland t are the lattice diffusivity and time respectively.

scholarly journals Exploration of the Transition from Harrison Type-A Kinetics to Type-B Kinetics Regimes in Grain Boundary Diffusion

2008 ◽  
Vol 273-276 ◽  
pp. 425-430 ◽  
Author(s):  
Irina V. Belova ◽  
Graeme E. Murch
Keyword(s):  
Grain Boundary ◽  
Transition Point ◽  
Boundary Diffusion ◽  
Diffusion Length ◽  
3D Structure ◽  
Type A ◽  
Tracer Diffusion ◽  
Diffusion Problem ◽  
Grain Boundary Diffusion ◽  
Type B

We model the grain boundary tracer diffusion problem by constructing a 3D structure consisting of cubic grains each of equal volume. We build the structure in such a way that no four cubes have a common edge. It is shown that the transition point between Harrison Type-A and Type-B kinetics regimes occurs at a diffusant diffusion length roughly an order of magnitude smaller than for the extensively studied case of parallel grain boundary slabs. For two dimensional squares the transition point occurs at a diffusion length roughly a factor of five smaller than for parallel grain boundary slabs. Thus we can draw the conclusion that dimensionality and geometric shape are both important factors in the parametric analysis of the grain boundary diffusion problem.

Diffusion and Migration of Ions in Sedimentary Rock Matrix: Effects of Ionic Strength and Tracer Concentration on Diffusion of Cs+ ions in Sandstone

2003 ◽  
Vol 807 ◽  
Author(s):  
Haruo Sato
Keyword(s):  
Ionic Strength ◽  
Matrix Effects ◽  
Chemical Properties ◽  
Effective Diffusivity ◽  
Concentration Profiles ◽  
Tracer Concentration ◽  
And Migration ◽  
Physical And Chemical ◽  
Cs Ions ◽  
And Chemical Properties

ABSTRACTIn-diffusion experiments for Cs+ and I− in sandstone were performed as a function of ionic strength ([NaCl]=0.01, 0.51M) and tracer concentration ([CsI]=7.5E-5, 1.5E-2M) together with the measurements of the physical and chemical properties of sandstone, and apparent diffusivities (Da) for Cs+ were obtained. The obtained Da-values for Cs+ scarcely depended on [NaCl], but increased with increasing [Cs+]. This trend is consistent with that of rock capacity factors (α), indicating that distribution coefficient (Kd) onto sandstone and effective diffusivity scarcely depend on [NaCl]. The concentration profiles of I− were all in already breakthrough. Although this indicates that I− diffusion is faster than that of Cs+, the concentration profiles of I− may have been lower than those for blank samples, judging synthetically from the correlations between α-values and the concentration profiles of Cs+ and from the concentration profiles of I− in the blank samples. Finally, the effects of [Cs+] and[NaCl] on Kd/-values for Cs+ were discussed from the viewpoint of adsorption by ion exchange and electrostatic attraction. The kd-values were considered to be combined sorption by both reactions.

Diffusion-Induced Grain Boundary Migration and Role of Defects

1993 ◽  
Vol 319 ◽  
Author(s):  
T.K. Chaki
Keyword(s):  
Free Energy ◽  
Grain Boundary ◽  
Boundary Migration ◽  
Solute Concentration ◽  
Grain Boundary Migration ◽  
Thermally Activated ◽  
Energy Of Mixing ◽  
Free Energy Of Mixing ◽  
Liquid Film Migration ◽  
Lattice Diffusivity

AbstractA model is presented to explain various aspects of diffusion-induced grain boundary migration (DIGM). The driving energies of DIGM are identified as the free energy of mixing and the interface free energy, the former being predominant in most cases of DIGM. The grain boundary migrates due to thermally activated motion of atoms across the interface under the influence of the driving energies. An expression for the velocity of migration is derived. It is shown that this depends parabolically on the solute concentration, in agreement with experimental observations in the case of liquid film migration (LFM), which is analogous to DIGM. Furthermore, the velocity is proportional to lattice diffusivity ahead of the boundary. Recent results of enhancement of DIGM by ion bombardment is explained by radiation-enhanced lattice diffusivity due to introduction of point defects by the ions. The model also explains that diffusion-induced recrystallization (DIR) is due to a free energy decrease associated with the transformation from the amorphous phase in the grain boundary layer to the crystalline phase.

Ion-beam mixing of Ni/Pd layers: II. Thermally assisted regime (>500K)

1988 ◽  
Vol 3 (6) ◽  
pp. 1063-1071 ◽  
Author(s):  
U. G. Akano ◽  
D. A. Thompson ◽  
W. W. Smeltzer ◽  
J. A. Davies
Keyword(s):  
Grain Boundary ◽  
Ion Irradiation ◽  
Ion Beam ◽  
Effective Diffusivity ◽  
Bilayer Films ◽  
Diffusion Analysis ◽  
The Mean ◽  
Atomic Mixing ◽  
Lattice Diffusivity

Atomic mixing in Ni/Pd bilayer films due to 120 keV Ar+ irradiation in the thermally assisted regime (523−673 K) has been measured, in situ, using Rutherford backscattering with 2.0 MeV 4He+ ions. The mean diameter of grains in these polycrystallinc films increased from 10 to 60 nm, following Ar+ bombardment at 573 K. Initial mixing was rapid due to grain boundary diffusion and incorporation of the metal solute into the solvent metal matrix by grain growth; this mixing stage was essentially complete within 10 min for annealed films or after an Ar+ dose of 4 × 1015 cm−2 in irradiated films (10 min irradiation). No further measurable mixing occurred in the annealed, unirradiated films. For the irradiated samples the initial rapid mixing (6−35 atoms/ion) was followed by a slower mixing stage of 0.7–1.8 atoms/ion for irradiation doses of up to 2.5 × 1016 Ar+ cm−2. The Ar+ bombardment gave rise to much smaller mixing levels when the Pd films were deposited on large-grain or single-crystal Ni. A diffusion analysis demonstrates that the effective diffusivity, Deff, for ion-irradiation-enhanced mixing in the thermally assisted regime satisfied the relation Dl < Deff < DB, where the ratio of the grain boundary to lattice diffusivity was DB/Dl > 106.

Diffusion of Sr in Bi2Sr2Can–1CunO2n+4

1993 ◽  
Vol 8 (10) ◽  
pp. 2465-2470 ◽  
Author(s):  
Nan Chen ◽  
S.J. Rothman ◽  
J.L. Routbort
Keyword(s):  
Diffusion Equation ◽  
Oxygen Partial Pressure ◽  
Partial Pressure ◽  
Pressure Range ◽  
Tracer Diffusion ◽  
Concentration Profiles ◽  
Measured Temperature ◽  
Serial Sectioning ◽  
Measured Temperature Range ◽  
Order Of Magnitude

Tracer diffusion of 85Sr in polycrystalline Bi2Sr2Can-1CunO2n+4 has been investigated for n = 1, 2, and 3 in an oxygen atmosphere between 775 and 850 °C. A radiotracer serial-sectioning technique was used to measure the concentration profiles, which were fit to a solution of the diffusion equation to calculate the diffusivities. The activation energies were 403, 553, and 519 kJ/mole, for n = 1, 2, and 3, respectively. However, the absolute values of D for the various layered superconductors did not differ by more than an order of magnitude over the measured temperature range. The diffusivity of Sr at 800 °C for n = 1 or 2 over an oxygen partial pressure range of 103 to 105 Pa increased as the pressure decreased.

Visualization of Grain Boundary as Blocking Layer for Oxygen Tracer Diffusion and a Proposed Defect Model in Non Doped BaTiO3Ceramics

2011 ◽  
Vol 4 (5) ◽  
pp. 055801 ◽  
Author(s):  
Ken Watanabe ◽  
Isao Sakaguchi ◽  
Shunichi Hishita ◽  
Naoki Ohashi ◽  
Hajime Haneda
Keyword(s):  
Grain Boundary ◽  
Tracer Diffusion ◽  
Blocking Layer ◽  
Defect Model ◽  
Oxygen Tracer
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