Diffusion Flashcards
What is diffusion?
Diffusion is the movement of atoms within a material.
EXAMPLE OF DIFFUSION
A carburized surface layer on a steel part.
Manufacturing a plastic bottles.
Oxidation of aluminium.
What is stability of atoms?
The ability of atoms and imperfections to diffuse increases as the temperature, or thermal energy, possessed by the atoms increases.
What is self diffusion ?
In materials containing vancancies, atoms move or jumps from a lattice possition to another.
What are the two important diffusion and explain them?
- Vacancy diffusion. An atom leave its lattice site to fill a nearby vacancy
- Interstitial diffusion When a small interstitial atom is present in the crystal structure, the atom moves from one interstial to another.
Give 3 type of diffusion and explain them
Volume Diffusion : The atoms move through the crystal from one regular or interstitial site to another. Because of the surrounding atoms, the activation energy is large and the diffusion rate is slow
Grain Boundary Diffusion : Atoms can diffuse easily by grain boundary diffusion because atom packing is poor at the grain boundaries. Atoms can squeeze easily.
Surface Diffusion : Surface diffusion is easier still because there is even less constraint on the diffusing atoms at the surface.
What does ficks first law states
Ficks first law states that the rate at which atoms , ions, particles or other species diffuse in a material can be measured by the flux (J). The flux is defined as the number of atoms passing through a plane of unit area per unit time
What factors affect diffusion ?
Temperature and the Diffusion Coefficient, grater surface area.
What is grain growth
Grain growth occurs as atoms diffuse across the grain boundary from one grain to another.
what is Diffusion bonding
Diffusion bondign is a joining technique in which two surfaces are pressed together at high pressure and temperatures.
what is Sintering
Sintering is a high temperature treatment used to join small particles and gradually reduces the volume of pore space between them.
