User-Defined Properties
Pandat™ allows user to define any property of a phase or a system following some simple syntax rules. The User-Defined Property database can be added to the original database, either TDB or PDB files, through Append database function. (Please refer to Section Append Database for the detailed description on Append database function). user can also add the User-Defined Property parameters into their home-developed TDB files to develop a combined database for User-Defined Property calculations.
Three methods are implemented in Pandat™ to add User-Defined-Properties, depending on the nature of the properties. Key words Phase_Property; System_Property and Property are used in the syntax respectively.
Phase Property is used to define a property of a phase with a similar expression which describes the Gibbs energy of a disordered solution phase. Let U be the user-defined phase property and it is expressed as:
|
(1) |
where xi is the molar fraction of component i and 
is the property of the pure component i, 
is the k-th order interaction parameter between components i and j. The syntax used in the TDB file are:
Type_Definition z PHASE_PROPERTY U 1 !
Type_Definition v GES AMEND_PHASE_DESCRIPTION * VARIABLE_X U !
In this definition, “v” is the identifier, “*” means any phase, and VARIABLE_X is the key word indicating X as the variable. The meaning of this definition is that any phase with the identifier “v” will use mole fractions (x) as the variables for property U.
System Property is used to define a property of a system with more than one phase. For a property in a system with multi-phase mixture, the property of the system is the weighted average of that of each phase. By default, the arithmetic mean is applied to a user defined Phase Property in a multi-phase system. For example, the user defines Phase Property U in a system with a and b two-phase mixture. The property of U of this system is calculated by
|
(2) |
If the simple arithmetic mean does not apply, more complicated expression can be defined by User through Command System Property. For example, the value of the system property can be calculated through the function:
|
(3) |
where Ua+b is the user defined property of U in a+b two phase region. Ua and Ub is the property U in a and b phase respectively; fa and fb are the phase fraction of a and b phase respectively. Mi are the i-th order of the additional parameters which are used to describe additional effects on the user defined property U.
The syntax for the System Property used in the TDB file is:
System_Property Sys_U 1 !
Parameter L(Sys_U, Alpha, Beta;0) 298.15 M0; 3000 N !
Parameter L(Sys_U, Alpha, Beta;1) 298.15 M1; 3000 N !
Using command Property, user can also define special properties associated with phases in the original database. Any phase property available from Pandat Table can be used for user-defined property, such as G, H, mu, and ThF. However, the star symbol in a property, like mu(*), cannot be used.
The syntax for the Property used in the TDB file is:
Property GFcc_GLiq 298.15 G(@Fcc)-G(@Liquid); 6000 N !
Below are several common User-Defined Properties. The related TDB files are included in the folder： "...\Pandat 2024\Pandat 2024 Examples\PanPhaseDiagram\User_Defined_Property".