Examples of SET_ALTERNATE_CONDITION

The following topics demonstrate how SET_ALTERNATE_CONDITION is used to prepare different kinds of equilibria for optimization in alternate mode.

If only one side of the tie-line has been measured, then you must provide an estimate of the composition of the other phase. You can make such an estimate with SET_ALTERNATE_CONDITION. This command has no effect unless alternate mode is turned on. The equilibrium described could thus be specified in the following way:

CREATE_NEW_EQUILIBRIUM 1 1

CHANGE_STATUS PHASE FCC BCC=FIX 1

SET_CONDITION P=1E5 T=1000

EXPERIMENT X(BCC,B)=.2:.01

SET_ALTERNATE_CONDITION X(FCC,B)=.3

When the alternate mode is turned on, the composition given by the SET_ALTERNATE_CONDITION command is used for the FCC phase. The properties of the BCC phase is calculated using the composition specified by experiment as a condition.

If you have a three-phase equilibrium in your POP file, then one of its compositions can be specified as experimentally determined, while two can be provided as alternate conditions:

CREATE_NEW_EQUILIBRIUM 1 1

CHANGE_STATUS PHASE FCC BCC LIQ=FIX 1

SET_CONDITION P=1E5

EXPERIMENT T=912:5 X(LIQ,B)=0.2:.02

SET_ALTERNATE_CONDITION X(FCC,B)=0.1 X(BCC,B)=.4

When you specify the composition of stoichiometric phase with SET_ALTERNATE_CONDITION, the value must be given with at least seven decimal digits, as in the following example:

CREATE_NEW_EQUILIBRIUM 1 1

CHANGE_STATUS PHASE LIQ A2B=FIX 1

SET_CONDITION P=1E5 X(LIQ,B)=0.2

EXPERIMENT T=992:5

SET_ALTERNATE_CONDITION X(A2B,B)=.6666667

The following table shows some additional examples of how to enter different kinds of experiments in the POP file when you are using the alternate mode.

Example

ED_EXP commands

Two-phase equilibrium: The melting temperature of an Au-Cu alloy

CHANGE_STATUS PHASE LIQUID FCC=FIX 1 SET_CONDITION X(FCC,CU)=0.14 P=1E5 EXPERIMENT T=970:2 SET_ALTERNATE_CONDITION X(LIQUID,CU)=0.16

Invariant equilibrium experiment: A three-phase equilibrium in a binary system

CREATE_NEW_EQUILIBRIUM 1 1 CHANGE_STATUS PHASE FCC BCC LIQUID=FIX 1 SET_CONDITION P=1E5

EXPERIMENT T=912:5 SET_ALTERNATE_CONDITION X(FCC,B)=0.1SET_ALTERNATE_CONDITION X(BCC,B)=0.4SET_ALTERNATE_CONDITION X(LIQ,B)=0.2

Ternary system, with two compositions measured (both with uncertainty 0.02)

CREATE_NEW_EQUILIBRUM 1 1 CHANGE_STATUS PHASE FCC BCC=FIX 1 SET_CONDITION T=1273 P=1E5 SET_CONDITION X(FCC,B)=0.1:0.02 EXPERIMENT X(FCC,C)=0.12:.02 SET_ALTERNATE_CONDITION X(BCC,B)=0.17 SET_ALTERNATE_CONDITION X(BCC,C)=0.07