MICRESS Forum

Dear Bernd,

I would like to ask about entropy of fusion which is used for calculation driving force in MICRESS.

When we perform calculation with coupling Thermo-Calc, entropy of fusion is output in TabLin file (i.e. dSf+ and dSf-).
On the other hand, I am not sure how to calculate entropy of fusion using only Thermo-Calc without using MICRESS.
If possible, could you please tell me how to do this?

I am so sorry to ask a question which is not related to MICRESS directly.
However, this method is very useful for defining entropy when doing calculations in MICRESS without coupling TQ.
Also, I would like to use MICRESS knowing the logic by which the value of entropy was calculated, not just trusting the value shown in the TabLin file.

Regards,
Chika

Hi Chika,

dSf+ and dSf- are calculated as derivatives of the driving force ΔG_αβ to temperature:

dSf+ = {dΔG_αβ/dT}_cα=const

dSf- = {dΔG_αβ/dT}_cβ=const

This is also the way it is used within MICRESS (extrapolation of ΔG with temperature). dSf+ and dSf- are practically identical for simple cases like solidification, but they can also be strongly different (even having different sign in systems which tend to demixing). We are taking the average of both in case of a moving interface.

Bernd

Dear Berned,

Thank you for your quick reply.
I have an additional question.

To calculate a derivative of the driving force using Thermo-Calc, does it mean that you calculate the free energy at the target temperature and that at a temperature slightly different from the target, and then consider the difference between them to be the derivative of the driving force?

Regards,
Chika

Hi Chika,

No, what you propose to do would result in the derivative of the free energy and not of the driving force!

You can calculate the driving force with Thermo-Calc if you set one phase ENTERED and the other phase DORMANT. Setting the total composition then corresponds to setting (i.e. fixing) the phase composition of the ENTERED phase. To obtain the temperature derivative of the driving force, you then can apply a step-wise temperature variation as you propose.

Bernd

Dear Bernd,

Sorry, I misunderstood the sentence of your previous reply!
I would like to try reproducing the entropy of fusion by using Thermo-Calc.

Regards,
Chika