Materials Balance


Concepts Shown:

phase diagrams, the Lever Rule, two phase regions


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


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.


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.



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