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[Databases] [Capillarity] [Programming] [Program list] |

This section is entirely specific to PT-group (in particular, the databases involved). It is possible to account for capillarity effects in MTDATA. This is done by adding a pressure dependency to the Gibbs energy of the phase which is subject to capillarity effect.

By raising the pressure, it is possible to add an arbitrary
constant to the Gibbs energy of some phases. In the following example
we evaluate the equilibrium between austenite and NbC for a particle
of 10 nm radius, assuming a interfacial energy of 0.2 J/m^{2}.

- No capillarity:
WHICH MODULE ? mu

MULTIPHASE OPTION ? def sy 'Fe,Nb,C' sou plus substances_p !

MULTIPHASE OPTION ? class ab p(*) no p(FCC_A1,CNb) !

MULTIPHASE OPTION ? set temp 1173 !

MULTIPHASE OPTION ? set w 100 !

MULTIPHASE OPTION ? set w( ) undef 0.1 0.05 !

MULTIPHASE OPTION ? set p 1 !

MULTIPHASE OPTION ? co pri ea_st_re !

which gives us, among other things:

Gibbs/Helmholtz Energy contributions per phase FCC_A1 -9.77875975659771E+07 CNb -2.27030944053310E+05 Mass/kg Phase Mass fraction of component within phase Fe Nb C 9.9890E+01 FCC_A1 0.9996034 0.0000226 0.0003740 1.1038E-01 CNb 0.0000000 0.8855195 0.1144805

- With capillarity, following the above:
MULTIPHASE OPTION ? set p 2.4E8 !

MULTIPHASE OPTION ? co pri ea_st_re !should give, among other things:

Gibbs/Helmholtz Energy contributions per phase FCC_A1 -9.77878593277758E+07 CNb -2.26264463200573E+05 Mass/kg Phase Mass fraction of component within phase Fe Nb C 9.9890E+01 FCC_A1 0.9996021 0.0000237 0.0003742 1.1026E-01 CNb 0.0000000 0.8855195 0.1144805

You note that, when defining the system, we have used the database
**plus** (as usual) and **substances_p**. The latter is the
modified database which contains data for: C0.749Nb, C0.877Nb,
C0.98Nb, CNb, CTi, NNb, NTi.

The pressure dependency has been set so that the Gibbs energy
increases by 10^{-6}J.mol^{-1}/Pa.

With the given data, and assuming a molar volume of
6x10^{-6}m^{-3}, the capillarity effects amounts to an
addition of 240 J/mol.

In the first calculation, the pressure is set to 1, so that the
addition is negligible (leaving the pressure to its default,
*i.e.* atm pressure, would also have negligible influence).
In the second example, it is set to 2.4x10^{8} Pa, resulting in
the required increase of Gibbs energy for NbC.

**m23c6_p**: modified data for M_{23}C_{6}. (sublattice1: Cr,Fe,Mn,Ni,V,Co; sublattice 2:Co,Cr,Fe,Mn,Mo,Ni,V,W; sublattice 3: C).**hcpa3_p**: as above for HCP_A3 (sublattice 1:Fe,Mo,Al,Cr,Cu,Mg,Mn,Nb,Ni,Si,Ti,V,W,Co; sublattice 2:C,N,Va)

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