Example 1.10: Calculation of Activity at Constant Temperature

Purpose: Learn to calculate activities of components in a system
Module: PanPhaseDiagram
Thermodynamic Database: Al_Demo.rtdb
Batch file: Example_#1.10.pbfx

Figure 1.10.1 is the Al-Mg binary phase diagram. In this example, we learn to calculate the activity of Al and Mg as a function of composition, x(Mg), at 300°C (the red dash line).

Figure 1.10.1: Al-Mg binary phase diagram

Calculation Method 1, From menu bar “Property”:

  • Load Al_Demo.rtdb following the procedure in Pandat User’s Guide: Load Database, and select Al and Mg two components;
  • Click “Property” on the menu bar and select “Thermodynamic Property”;
  • Set Calculation Condition as shown in Figure 1.10.2. The property selected is a(*), and the reference states are set as Fcc for Al and Hcp for Mg; (*) means the activity of every component (both Al and Mg in this case);

Figure 1.10.2: Calculation of the activity of Al and Mg from “Property” calculation

Calculation Method 2, From menu bar “PanPhaseDiagram”:

Post Calculation Operation:

Information obtained from this calculation:

  • Figure 1.10.3 shows the activities of Al and Mg as a function of x(Mg) using Fcc Al and Hcp Mg as reference states;
  • Activity of Al is 1 at x(Al)=1 (x(Mg)=0) since it is pure Fcc Al at this temperature and Fcc is used as the reference state; Activity of Al decreases with the increase x(Mg) and becomes zero at x(Mg)=1;
  • Activity of Mg is 0 at x(Al)=1 (x(Mg)=0) and increases with the increase x(Mg) and becomes 1 at x(Mg)=1;
  • Activity of either component is constant in a two-phase field.

Figure 1.10.3: Activities of Al and Mg in Al-Mg binary at 300°C