MTDATA – Phase Diagram Software from the National Physical Laboratory

 

 

 

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CLASSIFY

Function:

The CLASSIFY command is used to remove individual components, phases or substances from consideration in subsequent calculations or to reintroduce those previously removed, to establish reference states for the thermodynamic properties of components, to flag "PARA" components, the relative amounts of which are to be fixed in all phases in which they appear, and to indicate potential miscibility gaps in phases. It is also important in setting up open system calculations in that it allows appropriate computational parameters to be specified and the amounts of individual components to be set FREE to change.

Parameters:

absent

normal

reference(*)

free

delta(*)

miscibility(*)

para

Defaults:

normal = <all components, phases, substances (unless flagged as absent in the datafile)>

delta = <program defined>

misc = as flagged in the datafile or database

Examples:

classify absent phase(3) 1 2 7 !

classify normal component(1) !

classify absent "CO2<g>" 12 46 substance(13) !

classify misc(9) = 1 free component(3) !

classify reference(1) 2 !

classify absent all !

classify normal p(*) !

classify absent substance(13,15-17) !

classify para component(1) component(2) !

Parameter values:

ABSENT, NORMAL

take the value [component(*)] [phase(*)] [substance(*)]    [ ] = possible omission or repetition

The ABSENT parameter is used to remove selected COMPONENTs, SUBSTANCEs or PHASEs from consideration in subsequent phase equilibrium calculations. The NORMAL parameter is used to reintroduce COMPONENTs, SUBSTANCEs or PHASEs previously classified ABSENT. Although the default status of all COMPONENTs, SUBSTANCEs and PHASEs is NORMAL, certain SUBSTANCEs and PHASEs may be classified ABSENT automatically on reading thermodynamic data from a .mpi file (see DEFINE). SUBSTANCEs will be classified ABSENT, for example, if they are constrained never to form in the system under study. PHASEs will be classified ABSENT if their data is deemed to be incomplete.

COMPONENT(*), PHASE(*), SUBSTANCE(*)   removes from consideration or reintroduces those COMPONENTs, SUBSTANCEs and PHASEs listed in brackets using either their names or their numbers from the appropriate SYSTEM list (see LIST SYSTEM). An asterisk in brackets (*) is used to indicate all COMPONENTs, SUBSTANCEs or PHASEs in the currently DEFINEd system. Substances may also be indicated by specifying their numbers without the SUBSTANCE keyword.

DELTA(*)

takes the values <increment> / UNDEFINED

The DELTA(*) parameter is used to specify a step size for the amount of a FREE component, to be used as a basis for iteration towards an equilibrium constraint. This is effective only in BOTH_LARGE or STAGE_1 calculations (see COMPUTE). The component name or its number on the SYSTEM list should be given in brackets after the DELTA keyword. To cancel a previously established step size the value UNDEFINED should be entered.

In most cases it is best to allow the program to select its own step size. It will do this if DELTA is UNDEFINED.

FREE

takes the value COMPONENT(*)

The FREE parameter is used to indicate that the total amount of a particular component is to be varied by the program in order to meet equilibrium constraints imposed on substances containing that component.  The component name or its number on the SYSTEM list should be given in brackets after the COMPONENT keyword.

If oxygen, for example, as component number 2, were known to be present at equilibrium with an O2<g) partial pressure of 1x10-9 then the following commands might be entered:

set lgt_p(O2<g>) = -9 ! classify free comp(2) !

Care should be taken when setting equilibrium constraints since certain values might not have unique solutions in terms of the FREE component amounts required to achieve them. A warning is issued if an equilibrium constraint is SET without a corresponding FREE component classification.

A FREE classification can be cancelled by a subsequent NORMAL classification.

MISCIBILITY(*)

takes the value <number> / NONE

The MISCIBILITY parameter provides a mechanism for flagging phases which may exhibit miscibility gaps. The phase name or its number on the SYSTEM list should be given in brackets after the MISCIBILITY keyword, then the number of possible miscibility gaps should be entered. Possible values are 1, 2 or NONE, which cancels any previous MISCIBILITY classification giving the specified phase the status NORMAL. For example:

classify miscibility(9) = 1 miscibility(1) = none !
class misc(BCC) 2 !

MISCIBILITY classifications may appear automatically if data are read from a data input (.mpi) file which contains miscibility gap flags.

PARA

takes the value COMPONENT(*)

CLASSIFY PARA provides a mechanism for flagging “PARA” components, the relative amounts of which are to be fixed in all phases in which they appear. The component name or its number on the SYSTEM list should be given in brackets after the COMPONENT keyword. Each phase in the system under study must either contain all of the components classified as PARA or none of them.

As an example of a para-equilibrium calculation, C might be assumed to diffuse rapidly during transformations from ferrite (BCC_A2) to austenite (FCC_A1) in the Fe-Cr-C system, while Fe and Cr do not diffuse at all. Fe and Cr would then be classified as PARA components.

REFERENCE[(*)]

takes the values DEFAULT_REF_STATE/ <phase number> / <phase name> where [ ] indicates an optional entry

The REFERENCE parameter allows a reference phase to be established for each component present in the system under study. This allows thermodynamic properties such as Gibbs energy, enthalpy, chemical potential and activity to be referred to components in chosen phases. The component name or its number on the SYSTEM list should be given in brackets after the REFERENCE keyword. The phase name or its number on the SYSTEM list should then be provided as a value. For example:

classify refer(1) halite ref(SiO2) 7 !
classify reference liquid !

If no component name or number is given, the reference phase of every component is changed. The DEFAULT_REF_STATE is that implied in the data input (.mpi) file from which the thermodynamic data for the system under study were taken.

 
General comments:

None.

 

Updated 30 July 2010