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.

An example

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/m².

• 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
  

Explanations:

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^-6J.mol^-1/Pa.

With the given data, and assuming a molar volume of 6x10^-6m^-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 2.4x10⁸ Pa, resulting in the required increase of Gibbs energy for NbC.

Which database for which phase ?

• m23c6_p: modified data for M₂₃C₆. (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)