MTDATA – Phase Diagram Software from the National Physical Laboratory

 

 

 

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Selecting Components

The components of a system are defined and the data are recovered under the File|Newfile menu option in the Define New System Window. For the majority of practical applications the system is defined by its components separated by commas. Usually the components are elements, eg:

C,H,O,N,S
Fe,Cr,Ni

In the first example most of the possible products would be gases and stoichiometric compounds for which the first choice of data source would be the SGTE substance database. In the second example you would be interested in alloy phases, many of which are solutions, so you would chose the SGTE solution database. See also Data Sources.

If the purpose were to construct ternary phase diagrams it would be wise to enter the components in the order desired in the diagrams, starting with the component at bottom left and going clockwise. For binary diagrams the first named component also goes on the left.

  • After defining the system and the data source it is best to use the Save As option to give the resultant data file a specific name with the automatically added extension .mpi, eg: FeCrNi.mpi.
  • The components may also include compounds eg:
KCl,CaCl2,ZnCl2
  • Because there are four elements but only three components, the species recovered from the database(s) would be limited to the plane defined by the components. For example Zn would not be included.
  • In salt systems reciprocal reactions are possible, for example NaCl + KBr = NaBr + KCl, in which any three reactants can generate the fourth. As in the previous example, although there four elements the system is a ternary. Therefore the system can be defined by three components eg:
NaCl,KCl,KBr

Although the space occupied by the ternary diagram lies in a plane, it is not confined to a triangle but extends to a rectangle that includes not only NaCl, KCl and KBr but also NaBr. Again, the first named component will default to the bottom left corner.

This establishes the principle of reciprocal systems but in practice, because salts are ionic and so charged species are included in the model used in the salts database and the system should be defined as:

NaCl,KCl,KBr,Na/+

See also Selecting Components 2 which includes consideration of:
  • models
  • oxide systems
  • charged species
  • reference states
  • chemically non-reacting systems
  • isotopes.
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Updated 7 May 2010