Phase Diagrams

Question 1

Define solubility limit?

Answer 1

For many alloy systems and at some specific temperature, there is a max concentration of solute atoms that may dissolve in the solvent to form a solid solution: this is called a solubility limit.

The addition of solute in excess of solubility limit results in the formation of another solid or compound that has a distinctly different composition

Solubility depends on the relative shape and size of the atoms

We can plot the amount of one element or compound that is soluble in another against temp.
Read example in book pg 354

Question 2

Define phase?

Answer 2

• a phase is a homogenous portion of a system that has uniform physical and chemical characteristics.
• every pure material is considered to be a phase so also is every solid, liquid, gaseous solution. Eg dissolving sugar in water, the sugar-water syrup solution is one phase, solid sugar is another, each has different physical properties (liquid, solid) and chemical properties( diff chemical compositions)

Many substances are polymorphic and can change phase eg with temp

Question 3

What are polymorphic substances?

Answer 3

Polymorphism is the ability of a solid material to exist in more than one form or crystal structure.

Polymorphism can potentially be found in any crystalline material including polymers, minerals, and metals.

Question 4

What are phase diagrams used for?

Answer 4

To workout out..
1) how do materials in particular alloys change when heated/cooled ?

2) what is the effect of composition?
3) how does composition/temp affect structure?
4) and what effect does this have on mechanical properties?