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Questions and Answers
What is the mechanism of vacancy diffusion?
What is the mechanism of vacancy diffusion?
- An atom moves into an interstitial position, creating a new interstitial position
- An atom moves into the vacancy’s original position, creating a new vacancy in the atom’s original position (correct)
- An atom moves into the vacancy’s original position, creating a new interstitial position
- An atom moves into an interstitial position, creating a new vacancy in the atom’s original position
How does interstitial diffusion occur?
How does interstitial diffusion occur?
- Larger chemical species move between the spaces around smaller atoms
- Atoms move into the vacancies of other atoms
- Smaller chemical species move between the spaces around larger atoms (correct)
- Atoms move into the interstitial positions of other atoms
What does Fick’s First Law describe?
What does Fick’s First Law describe?
- The relationship between temperature and diffusion coefficient
- The mechanism of interstitial diffusion
- The change in concentration gradient over time
- How much of something moved and how fast did it move (correct)
What does steady-state diffusion imply?
What does steady-state diffusion imply?
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How does temperature affect diffusion?
How does temperature affect diffusion?
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Study Notes
Mechanism of Diffusion
- Vacancy diffusion: Occurs when an atom jumps into an adjacent vacant lattice site, resulting in a net movement of atoms.
- Interstitial diffusion: Takes place when an atom moves into an interstitial site, which is a space between lattice sites, without displacing any other atoms.
Fick's Laws
- Fick's First Law: Describes the rate of diffusion in a concentration gradient, stating that the flux of atoms is proportional to the concentration gradient and the diffusion coefficient.
- Fick's Second Law: Describes the change in concentration over time, stating that the rate of change of concentration is proportional to the second derivative of concentration with respect to position.
Characteristics of Diffusion
- Steady-state diffusion: Implies that the concentration gradient remains constant over time, resulting in a constant flux of atoms.
- Temperature effect: Diffusion rate increases with increasing temperature, as higher temperatures provide more energy for atoms to overcome their activation energy and diffuse.
Important Concepts
- Diffusion coefficient: A measure of the ease of diffusion, dependent on the material's properties and temperature.
- Concentration gradient: The change in concentration of atoms or molecules over a given distance.
- Flux: The rate of flow of atoms or molecules across a given area.
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