Title: Summary Part Diffusion 2

Choose the correct statement.

- The rate of thermally activated processes increase exponentially with temperature, as described by an Arrhenius expression. (correct)
- The rate of thermally activated processes decrease exponentially with temperature, as described by an Arrhenius expression.
- The rate of thermally activated processes increase linearly with temperature, as described by an Arrhenius expression.

- Solid-state diffusion in cystalline materials occurs via a point-defect mechanism – an atom hops into an adjacent vacancy in the crystal lattice (correct)
- Solid-state diffusion in cystalline materials occurs via two atoms changing places simultaneously.

- The diffusion coefficient (diffusivity) increases exponentially with temperature, following an Arrhenius expression. (correct)
- The diffusion coefficient (diffusivity) increases linearly with temperature, following an Arrhenius expression.
- The diffusion coefficient (diffusivity) is constant as a function of temperature for a given element.

- Atomic migration via diffusion is a random-walk process. (correct)
- Atomic migration via diffusion is a directional process.

- A concentration gradient of two materials can result in a directional flow of material, despite the random nature of individual atom movements. (correct)
- The random nature of individual atom movements prevents any directional flow of matter via diffusion.

- The mathematics of diffusion allows a relatively precise description of the chemical concentration profiles of diffusing species. (correct)
- As diffusion is a random walk process, mathematical description and prediction of diffusion and hence resulting concentration profiles is impossible.

- Volume or bulk diffusion is typically dominant in coarse-grained polycrystalline materials. In the case of fine-grained polycrystalline materials or powders, material transport may be dominated by grain-boundary diffusion of surface diffusion, respectively. (correct)
- Volume or bulk diffusion always dominates the diffusive material transport in a material – diffusion paths along grain boundaries or the surface are always slower than diffusion through the bulk.

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