Low-Temperature Grain Boundary Diffusion Data Measured from Historical Artifacts

2004 ◽  
Vol 852 ◽  
Author(s):  
R.J. Kremer ◽  
M.A. Dayananda ◽  
A.H. King
Keyword(s):  
Low Temperature ◽  
Grain Boundary ◽  
Room Temperature ◽  
Boundary Diffusion ◽  
Diffusion Processes ◽  
Grain Boundary Diffusion ◽  
Accelerated Tests ◽  
Temperature Diffusion ◽  
Diffusion Profiles

ABSTRACTDiffusion processes in typical metals are slow at room temperature but there are many applications for which very long-term use is envisaged and stability needs to be assured over a timescale of 10, 000 years, where even slow processes can be important. It is common to perform accelerated tests at higher temperatures and extrapolate the necessary information from the measurements so obtained. We have tested the validity of this type of extrapolation for room-temperature, grain boundary diffusion in the copper-silver system, by measuring low-temperature diffusion profiles in antique samples of Sheffield plate.

Room-temperature grain boundary diffusion data measured from historical artifacts

2005 ◽  
Vol 96 (10) ◽  
pp. 1187-1192 ◽  
Author(s):  
Raymond J. Kremer ◽  
Mysore A. Dayananda ◽  
Alexander H. King
Keyword(s):  
Grain Boundary ◽  
Room Temperature ◽  
Boundary Diffusion ◽  
Grain Boundary Diffusion ◽  
Diffusion Data

Intergranular Coupling and Grain Isolation of Thin Co Films

1998 ◽  
Vol 517 ◽  
Author(s):  
Heng Gong ◽  
Wei Yang ◽  
David N. Lambeth ◽  
David E. Laughlin
Keyword(s):  
Grain Boundary ◽  
Thermal Instability ◽  
Boundary Diffusion ◽  
Oxidation Process ◽  
Diffusion Processes ◽  
Narrow Range ◽  
Grain Boundary Diffusion ◽  
Temperature Dependent ◽  
In Situ Diffusion

AbstractThe effects of rapid oxidation and overcoat diffusion processes on the intergranular coupling and grain isolation in thin Co films were studied. The oxidation process was found to be strongly temperature dependent. The optimal coercivities can only be achieved within a narrow range of temperatures, while further increasing the temperature incurs significant thermal instability. CrMn underlayers were confirmed to be more effective in enhancing the grain isolation by the grain boundary diffusion during the oxidation process. The oxidation process does not change the Co anisotropy, and hence the coercivity increase is appears to be a result of better grain isolation. The in-situ diffusion of Ag and Cr overcoats were also found to have siginificant effects on the grain isolation in Co and CoCr films.

Numerical Study of Grain Boundary Diffusion in Nanocrystalline Materials

2005 ◽  
Vol 237-240 ◽  
pp. 1043-1048 ◽  
Author(s):  
D. Gryaznov ◽  
J. Fleig ◽  
Joachim Maier
Keyword(s):  
Grain Boundary ◽  
Nanocrystalline Materials ◽  
Boundary Diffusion ◽  
Nanocrystalline Material ◽  
Numerical Study ◽  
Average Length ◽  
Type A ◽  
Grain Boundary Diffusion ◽  
Conventional Models ◽  
Diffusion Profiles

Diffusion in nanocrystalline materials is becoming an increasingly important topic. The analysis of diffusion profiles obtained in nanocrystalline materials with enhanced grain boundary diffusion, however, is not straightforward since assumptions made in the deviation of the conventional models are often not fulfilled. In this contribution numerical diffusion studies are performed in order to investigate effects caused by the high density of interfaces in nanocrystalline material. A continuum model based on the 2D 2-nd Fick’s law was solved by means of the finite element method. This allows us to analyze diffusion profiles for different geometrical situations such as a single boundary, square grains with the grain size of 80 nm and 25 nm and geometries comprising differently oriented boundaries of the average length of 30 nm . The analysis was carried out for different diffusion lengths corresponding to Harrison type A and type B kinetic regimes. For the isolated boundary a very good agreement was achieved in comparison with the classical Whipple’s solution. For nanocrystalline material, however, considerable errors can occur when analyzing the averaged diffusion profiles in the conventional Harrison type A and B kinetics.

Mechanistic Two Stage Fission Gas Release Model

2002 ◽  
Author(s):  
Yong-Soo Kim ◽  
Chan-Bok Lee
Keyword(s):  
Grain Boundary ◽  
Diffusion Coefficients ◽  
Boundary Diffusion ◽  
Diffusion Processes ◽  
Lattice Diffusion ◽  
Grain Boundary Diffusion ◽  
Factor Α ◽  
Two Stages ◽  
Grain Surface ◽  
Release Model

In this study, a mechanistic two stages model is developed which analytically simulates the two-step diffusion processes, grain lattice diffusion and grain boundary diffusion, coupled with the bubbles trap/resolution. Mathematical manipulation reveals that the release at high burn-up depend on the ratio of the diffusivities in the both processes, i.e., α ≅ Dveff/Dgbeff where Dveff and Dgbeff are effective volume and grain boundary diffusion coefficients, respectively. Thus, the ratio α is incorporated in the time-dependent third kind boundary condition at the equivalent grain surface. This model brings forth analytical solutions of the fractional release which are identical to that of either ANS5.4 or modified ANS5.4 model when α goes to the infinity. It turns out that this model describes the release behavior well in the high burn-up fuel and puts out a comparable prediction to the solution of FRAPCON-3 model under the same condition. It is also demonstrated that the new factor α not only ease the computational treatment for the high burn-up fuel performance evaluation, but also enables us to possibly separate the burn-up enhancement from the diffusion coefficients and to easily simulate the bubble-related phenomena in the grain boundary.

Diffusion Mechanisms in Nanocrystalline and Nanolaminated Au-Cu

2007 ◽  
Vol 266 ◽  
pp. 13-28 ◽  
Author(s):  
Alan F. Jankowski
Keyword(s):  
Low Temperature ◽  
Grain Boundary ◽  
Grain Growth ◽  
Boundary Diffusion ◽  
Bulk Diffusion ◽  
Grain Boundary Diffusion ◽  
Dominant Mechanism ◽  
Temperature Range ◽  
Diffusion Mechanisms ◽  
Kinetics Of

Thermal anneal treatments are used to identify the temperature range of the two dominant diffusion mechanisms – bulk and grain boundary. To assess the transition between mechanisms, the low temperature range for bulk diffusion is established utilizing the decay of static concentration waves in composition-modulated nanolaminates. These multilayered structures are synthesized using vapor deposition methods as thermal evaporation and magnetron sputtering. However, at low temperature the kinetics of grain-boundary diffusion are much faster than bulk diffusion. The synthesis of Au-Cu alloys (0-20 wt.% Cu) with grain sizes as small as 5 nm is accomplished using pulsed electro-deposition. Since the nanocrystalline grain structure is thermally unstable, these structures are ideal for measuring the kinetics of grain boundary diffusion as measured by coarsening of grain size with low temperature anneal treatments. A transition in the dominant mechanism for grain growth from grain boundary to bulk diffusion is found with an increase in temperature. The activation energy for bulk diffusion is found to be 1.8 eV·atom-1 whereas that for grain growth at low temperatures is only 0.2 eV·atom-1. The temperature for transitioning from the dominant mechanism of grain boundary to bulk diffusion is found to be 57% of the alloy melt temperature and is dependent on composition.

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.

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