Sr-Diffusion in Ce0.8Gd0.2O2-δ Layers for SOFC Application

2013 ◽  
Vol 1542 ◽  
Author(s):  
Tabea Mandt ◽  
Carsten Korte ◽  
Uwe Breuer ◽  
Alexander Weber ◽  
Mirko Ziegner ◽  
...  
Keyword(s):  
Activation Energy ◽  
Grain Boundary ◽  
Barrier Layer ◽  
Boundary Diffusion ◽  
Bulk Diffusion ◽  
Grain Boundary Diffusion ◽  
Diffusion Activation Energy ◽  
Boundary Density ◽  
Long Term Stability ◽  
Maximum Lifetime

ABSTRACTIn this study Sr2+ diffusion along Ce0.8Gd0.2O2-δ (CGO) grain boundaries is investigated. Model samples with different grain boundary densities were prepared by different thin film tech-niques. Diffusion experiments were performed by annealing and subsequent ToF-SIMS analysis. The activation energy of grain boundary diffusion is determined as 492 kJ/mol, which is 2/3 of the bulk diffusion activation energy 739 kJ/mol, deduced from literature data [1-5].The formation of an electrical blocking SrZrO3 layer due to grain boundary diffusion of Sr2+ through a CGO barrier layer may limit the long term stability of Solid Oxide Fuel Cells based on Zr0.85Y0.15O2-δ electrolytes and La0.58Sr0.4Co0.2Fe0.8O3-δ cathodes. The grain boundary diffusivity and the CGO grain boundary density highly influence the kinetic of the SrZrO3 formation. Aim of this study is to gain data for a prediction of the maximum lifetime of a SOFC system, limited by the increasing cell resistivity due to SrZrO3 formation. Specifications for the CGO barrier layer preparation concerning grain boundary density are determined.

Study of Fe Diffusion in Cr2O3 by Secondary Ion Mass Spectrometry

2005 ◽  
Vol 237-240 ◽  
pp. 940-945
Author(s):  
Antônio Claret Soares Sabioni ◽  
Anne Marie Huntz ◽  
F. Silva ◽  
François Jomard
Keyword(s):  
Mass Spectrometry ◽  
Activation Energy ◽  
Grain Boundary ◽  
Boundary Diffusion ◽  
Secondary Ion Mass Spectrometry ◽  
Bulk Diffusion ◽  
Grain Boundary Diffusion ◽  
Iron Diffusion ◽  
Ion Mass Spectrometry ◽  
Secondary Ion

Chromia protective layers are used to prevent corrosion by oxidation of many alloys, such as the stainless steels, for instance. To check if chromia is a barrier to the outward diffusion of iron in these alloys, iron diffusion in chromia was studied in both polycrystals and oxide films formed by oxidation of Ni-30Cr alloy in the temperature range 700-1100°C at an oxygen pressure equal to 10-4 atm. An iron film of about 70 nm thick was deposited on the chromia surface, and after the diffusing treatment, the iron depth profiles were established by secondary ion mass spectrometry (SIMS). Using a solution of the Fick’s second law for diffusion from a thick film, effective or bulk diffusion coefficients were determined in a first penetration domain. Then, Le Claire’s and Hart’s models allowed both the bulk diffusion coefficient and the grain boundary diffusion parameter (aDgbd) to be obtained in a second penetration domain. Iron bulk and grain boundary diffusion does not vary significantly according to the nature-microstructure of chromia. The activation energy of grain boundary diffusion is at least equal or even greater than the activation energy of bulk diffusion, probably on account of segregation phenomena. Iron diffusion was compared to cationic self-diffusion and related to the protective character of chromia.

About Fe Diffusion in Cu

2012 ◽  
Vol 323-325 ◽  
pp. 171-176 ◽  
Author(s):  
D. Prokoshkina ◽  
A.O. Rodin ◽  
V. Esin
Keyword(s):  
Activation Energy ◽  
Diffusion Coefficient ◽  
Grain Boundary ◽  
Temperature Dependence ◽  
Boundary Diffusion ◽  
Bulk Diffusion ◽  
Grain Boundary Diffusion ◽  
Radiotracer Technique ◽  
Exponential Factor ◽  
Temperature Range

The temperature dependence of the bulk diffusion coefficient of Fe in Cu is determined by EDX in the temperature range from 923 to 1273 K, , m2/s. These results are different from that obtained earlier by radiotracer technique: activation energy is less by 30 kJ/mol and pre-exponential factor is 50 times smaller. Deviations from ideality of investigated solutions do not explain the differences; consequently, the thermodynamical factor would not responsible for such an effect. Fast grain boundary diffusion of Fe in Cu was not observed in the temperature range from 823 to 1073 K.

The Activation Energy of Superplastic Flow above the Critical Temperature for Steel CrWMn

2007 ◽  
Vol 551-552 ◽  
pp. 341-345
Author(s):  
J.B. Wen ◽  
F.X. Chen ◽  
Ke Ke Zhang ◽  
Yong Shun Yang
Keyword(s):  
Activation Energy ◽  
Critical Temperature ◽  
Grain Boundary ◽  
Strain Rate ◽  
Superplastic Deformation ◽  
Boundary Diffusion ◽  
Grain Boundary Diffusion ◽  
Diffusion Activation Energy ◽  
Sensitivity Index ◽  
Deformation Activation Energy

By means of superplastic tensile test above the Ac1 temperature (γ→α transformation temperature), superplastic deformation activation energy of ultrafine-grained commercial die steel CrWMn is investigated on the basis of the Arrhenius theory equation, exp( / ) 1 ε& = Aσ m −Q RT , which indicates the resistance of the superplastic deformation. According to the Arrhenius equation, the activation energy is estimated from the log σt vs 1/T relationship at a constant of sensitivity index of strain rate. The results show that the strain rate sensitivity index is a constant and rather high at the conditions of superplastic deformation for the CrWMn steel, the activation energy for superplastic deformation of steel CrWMn above the critical temperature is 187KJ/mol, and the superplastic deformation activation energy is approached to the grain boundary diffusion activation energy of γ-Fe. This indicates that the grain boundary sliding (GBS) in superplastic deformation of CrWMn steel is controlled by grain boundary diffusion. The characters of superplastic deformation of the steel above the critical temperature, on the other hand, are also analyzed in this paper.

scholarly journals Grain boundary diffusion and its relation to segregation of multiple elements in yttrium aluminum garnet

2020 ◽  
Vol 32 (6) ◽  
pp. 675-696
Author(s):  
Joana Polednia ◽  
Ralf Dohmen ◽  
Katharina Marquardt
Keyword(s):  
Grain Boundary ◽  
Boundary Diffusion ◽  
Yttrium Aluminum Garnet ◽  
Bulk Diffusion ◽  
Element Distribution ◽  
Grain Boundary Diffusion ◽  
Yttrium Aluminum ◽  
Detectable Concentration ◽  
Thin Film Diffusion ◽  
Strong Segregation

Abstract. We studied grain boundary diffusion and segregation of La, Fe, Mg, and Ti in a crystallographically defined grain boundary in yttrium aluminum garnet (YAG). Bi-crystals were synthesized by wafer bonding. Perpendicular to the grain boundary, a thin-film diffusion source of a La3.60Al4.40O12 was deposited by pulsed laser deposition. Diffusion anneals were performed at 1000 and 1450 ∘C. Via a gas phase small amounts of elements were added during the experiment. The element concentration distributions in our bi-crystals were mapped using analytical transmission electron microscopy (ATEM). Our results show strong segregation of La and Ti at the grain boundary. However, in the presence of Ti, the La concentrations dropped below the detection limit. Quantitative element distribution profiles along and across the grain boundary were fitted by a numerical diffusion model for our bi-crystal geometry that considers the segregation of elements into the grain boundary. The shape of the diffusion profiles of Fe requires the presence of two diffusion modes, e.g., the co-diffusion of Fe2+ as well as Fe3+. The absence of a detectable concentration gradient along the grain boundary in many experiments allows a minimum value to be determined for the product of sDgb. The resulting sDgb are a minimum of 7 orders of magnitude larger than their respective volume diffusion coefficient, specifically for La = 10−14 m2 s−1, Fe = 10−11 m2 s−1, Mg = Si = 10−12 m2 s−1, and Ti = 10−14 m2 s−1 at 1450 ∘C. Additionally, we model the effect of convolution arising from the given spatial resolution of our analysis with the resolution of our modeled system. Such convolution effects result in a non-unique solution for the segregation coefficient, e.g., for example for Mg between 2–3. Based on our data we predict that bulk diffusion of impurities in a mono-phase polycrystalline aggregate of YAG is effectively always dominated by grain boundary diffusion.

Grain Boundary Diffusion in Co/Cu and Co/Cr Magnetic Thin Films

1993 ◽  
Vol 313 ◽  
Author(s):  
John G. Holl-Pellerin ◽  
S.G.H. Anderson ◽  
P.S. Ho ◽  
K.R. Coffey ◽  
J.K. Howard ◽  
...  
Keyword(s):  
Thin Films ◽  
Activation Energy ◽  
Diffusion Coefficient ◽  
Grain Boundary ◽  
Photoelectron Spectroscopy ◽  
Boundary Diffusion ◽  
Magnetic Thin Films ◽  
Grain Boundary Diffusion ◽  
X Ray ◽  
Before And After

ABSTRACTX-ray photoelectron spectroscopy (XPS) has been used to investigate grain boundary diffusion of Cu and Cr through 1000 Å thick Co films in the temperature range of 325°C to 400°C. Grain boundary diffusivities were determined by modeling the accumulation of Cu or Cr on Co surfaces as a function of time at fixed annealing temperature. The grain boundary diffusivity of Cu through Co is characterized by a diffusion coefficient, D0gb, of 2 × 104 cm2/sec and an activation energy, Ea,gb, of 2.4 eV. Similarly, Cr grain boundary diffusion through Co thin films occurs with a diffusion coefficient, Do,gb, of 6 × 10-2cm2/sec and an activation energy, Ea,gb of 1.8 eV. The Co film microstructure has been investigated before and after annealing by x-ray diffraction and transmission electron Microscopy. Extensive grain growth and texturing of the film occurred during annealing for Co deposited on a Cu underlayer. In contrast, the microstructure of Co deposited on a Cr underlayer remained relatively unchanged upon annealing. Magnetometer Measurements have shown that increased in-plane coercivity Hc, reduced remanence squareness S, and reduced coercive squareness S* result from grain boundary diffusion of Cu and Cr into the Co films.

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.

Grain boundary Diffusion of Ni through Pd2Si

1983 ◽  
Vol 25 ◽  
Author(s):  
E. C. Zingu ◽  
J. W. Mayer
Keyword(s):  
Thin Film ◽  
Activation Energy ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Boundary Diffusion ◽  
Rutherford Backscattering Spectrometry ◽  
High Mobility ◽  
Grain Boundary Diffusion ◽  
Rutherford Backscattering

ABSTRACTInterdiffusion in the Si<100>/Pd2Si/Ni and Si<111>/Pd2Si/Ni thin film systems has been investigated using Rutherford backscattering spectrometry. Nickel is found to diffuse along the grain boundaries of polycrystalline Pd2Si upon which it accumulates at the Si<100>Pd2Si interface. The high mobility of Ni compared to that of si suggests that Pd diffuses faster than Si along the Pd2Si grain boundaries. An activation energy of 1.2 eV is determined for Ni grain boundary diffusion in Pd2Si.

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