Скачать или смотреть AMIE Exam Lectures- Material Science and Engineering | Diffusion in Solids| Types | Mechanism| 5.1

Engineering Subjects: Introduction to Material Science and Engineering:

Material Science and Engineering| Diffusion in Solids| Types of Diffusion| Diffusion Mechanism| 5.1

Review:
In the previous set of videos, we had seen the different kinds of imperfections that can be present in a solid material.

In the next 3 lectures, we shall be discussing about diffusion:
• What is diffusion?
• What is the basic phenomenon behind it?
• What are the different types of diffusion processes?

What is Diffusion:-
We have already studied diffusion in our junior classes but they are specific to gases.
Similar to that phenomenon, diffusion can take place even in solids.

Let us understand the basic phenomenon of diffusion:- 00:01:00
It is the process of mass transport by movement of atoms and molecules from a region of high chemical potential to a region of low chemical potential.
High chemical potential most of the time corresponds to High concentration
Low chemical potential most of the time corresponds to Low concentration

There are two types of diffusion:
• Interdiffusion or impurity Diffusion
• Self-Diffusion

Interdiffusion or impurity Diffusion:-
If a material of iron has some carbon molecules present and the carbon molecules diffuse and move to a different place then this is called Interdiffusion or Impurity Diffusion, because small amount of carbon in the bulk Iron is considered to be an impurity.

Self-Diffusion:-
If some iron molecules from the bulk iron material diffuse and shift to a new location then this is called Self Diffusion.

Diffusion Mechanism:-
How diffusion takes place?
During diffusion a step by step movement of atom takes place from one lattice site to another.
The requirements or diffusion to take place are
1. There should be an adjacent vacant site
2. Sufficient energy to break bond with neighbours
Where will the atom get energy to break the bonds?
Atomic vibration provides the required energy to break free the bond. More the temperature more would be the vibration and more energy to break free the bond.

There are two different mechanisms of diffusion
• Vacancy Diffusion
• Interstitial Diffusion

Vacancy Diffusion:–
As the name suggests, this has got to do something with vacancy.
Interchange of atom from normal lattice site with adjacent vacancy.
Ease depends on vacancy concentration.
Direction of movement of atom and vacancy is opposite to each other.
Both "Self diffusion" as well as "interdiffusion" takes place

Interstitial Diffusion:–
Interstitial are small pockets of empty spaces between atoms. When atoms are packed they have a packing fraction which would be less than 100%, so there is some space between atoms.
Small impurities can lie in between the atoms in these voids or empty space.
No vacancy required, no breaking of bonds required but the impurities or smaller atoms move through these vacancies.
Normally the atom moving is the impurity particle smaller in size.
Interstitial diffusion is faster as the atoms moving through the vacancy are smaller and the space between atoms is far more than the vacancy in vacancy diffusion.
We have seen
• What diffusion is?
• Diffusion takes place even solid
• Different types of Diffusion
• Different Diffusion Mechanism
• Temperature is an important criterion to tell how fast diffusion can take place

In the next video, we shall see further and build on what we have seen today.

A video by Edupedia World (www.edupediaworld.com), free online education

Click here for more videos on this topic:
https://www..com/playlist?list=PLJumA3phskPFPkGEkQe6YWZs8Z1-9xkkg

All Rights Reserved.