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A model for time-dependent grain boundary diffusion of ions and electrons through a film or scale, with an application to alumina
- Publication Year :
- 2017
- Publisher :
- arXiv, 2017.
-
Abstract
- A model for ionic and electronic grain boundary transport through thin films, scales or membranes with columnar grain structure is introduced. The grain structure is idealized as a lattice of identical hexagonal cells – a honeycomb pattern. Reactions with the environment constitute the boundary conditions and drive the transport between the surfaces. Time-dependent simulations solving the Poisson equation self-consistently with the Nernst-Planck flux equations for the mobile species are performed. In the resulting Poisson-Nernst-Planck system of equations, the electrostatic potential is obtained from the Poisson equation in its integral form by summation. The model is used to interpret alumina membrane oxygen permeation experiments, in which different oxygen gas pressures are applied at opposite membrane surfaces and the resulting flux of oxygen molecules through the membrane is measured. Simulation results involving four mobile species, charged aluminum and oxygen vacancies, electrons, and holes, provide a complete description of the measurements and insight into the microscopic processes underpinning the oxygen permeation of the membrane. Most notably, the hypothesized transition between p-type and n-type ionic conductivity of the alumina grain boundaries as a function of the applied oxygen gas pressure is observed in the simulations. The range of validity of a simple analytic model for the oxygen permeation rate, similar to the Wagner theory of metal oxidation, is quantified by comparison to the numeric simulations. The three-dimensional model we develop here is readily adaptable to problems such as transport in a solid state electrode, or corrosion scale growth.
- Subjects :
- Technology
Materials science
Polymers and Plastics
MASS-TRANSFER
Materials Science
Alumina
0204 Condensed Matter Physics
Ionic bonding
FOS: Physical sciences
Materials Science, Multidisciplinary
02 engineering and technology
01 natural sciences
Mass transfer
Grain boundary diffusion
0103 physical sciences
POLYCRYSTALLINE ALUMINA
Grain boundary diffusion coefficient
PERMEABILITY
Boundary value problem
OXYGEN POTENTIAL GRADIENTS
0912 Materials Engineering
Materials
010302 applied physics
Condensed Matter - Materials Science
Science & Technology
CHANNELS
AL2O3
Metals and Alloys
Materials Science (cond-mat.mtrl-sci)
Permeation
021001 nanoscience & nanotechnology
TRANSPORT
Electronic, Optical and Magnetic Materials
THERMAL BARRIER COATINGS
ALPHA-AL2O3
Membrane
Ceramic membrane
Chemical physics
Ceramics and Composites
Oxide-film growth kinetics
Poisson-Nernst-Planck
Metallurgy & Metallurgical Engineering
Grain boundary
Poisson's equation
0210 nano-technology
HIGH-TEMPERATURES
0913 Mechanical Engineering
Subjects
Details
- Database :
- OpenAIRE
- Accession number :
- edsair.doi.dedup.....3165052525f5865d4331c5538f04d8bd
- Full Text :
- https://doi.org/10.48550/arxiv.1702.01333