# Materials Balance

##### Concepts Shown:

phase diagrams, the Lever Rule, two phase regions

##### Equipment:

a transparency of the Cu / Ag phase diagram attached, transparencies of the other two sheets attached to this report.

##### Procedure:

First, show the class the phase diagram of Cu and Ag. then show them the first page of what I had typed up concerning the number of atoms in each phase. Simply go through it with the class and explain to them how I got the answers that I did. It is pretty self explanatory.

##### Science:

In MSE 250, students are often confused in distinguishing the compositions of phases and the amounts of phases in a two phase region on the phase diagram. Hopefully this exercise will help to aid that confusion. It simply consists of taking 1,000 atoms of a Cu / Ag alloy at 800 degrees Celsius and a 80 a/o Cu, and figures out how many atoms of each metal exist in each plane (Liquid or Beta). This is something that I think would help students understand the complete materials balance that exists on every point of a phase diagram. The students should be told that this exercise can be performed at every location on the diagram. Note: The numbers that I have used for the compositions of each phase at 800 degrees may not be precise. I simply judged from the diagram what these calculations were. Also, in calculating the number of Cu and Ag atoms in the phases, I came up with numbers with fractions so I rounded the answers to a whole number. That is why I used the ~ sign instead of the = sign. I did this because it wouldn't make sense to have an answer with fractions of an atom.