MatCalc uses an International System of Units (known also as SI) and all variables are by default expressed in the units specified in this system. The compositions are by default expressed in mole fractions. The intensive variables refer to mole of substance by default.

In some cases, the values might be expressed also in the other units. This is done by the attachment of the 'unit qualifiers' which are suffixes attached to the variable's name, after the usual '$' (conjunction symbol). More than one unit qualifier can be applied. Some examples are shown below with the unit qualifiers underlined:

'*T*' → Temperature expressed in Kelvin (default unit).

'*T$C*' → Temperature expressed in Celsius degrees.

'*F$FCC_A1*' → Phase fraction of FCC_A1 phase expressed in mole fraction (default unit).

'*F$FCC_A1$P*' → Phase fraction of FCC_A1 phase expressed in mole percent.

'*X$BCC_A2$C*' → Carbon content of BCC_A2 phase expressed in mole fraction (default unit).

'*X$BCC_A2$C$WP*' → Carbon content of BCC_A2 phase expressed in weight percent.

Below is the list of the available unit qualifiers:

Unit qualifier | Meaning | Comment |
---|---|---|

C | degree Celsius | relevant for temperature |

K | mass | relates the intensive variables to one kilogram of a phase |

V | volume |
relates the intensive variable to one cubic meter of a phase, valid only with physical database read |

W | weight content | relevant for phase fractions, phase compositions |

P | percent | multiplies the value by 100 |

X | inverse | returns the inverse value |

L | natural logarithm | returns the natural logarithm of the value |

G | common logarithm | returns the common logarithm of the value |

As the first approximation, the densities of all phases in the system can be assumed to be the same. In this case, the phase fractions expressed in volume fraction are the same as the ones in mole fraction, i.e. these can be represented by the '*F$Phase'* variable value.

The actual differences can be noticed when a physical database ('*.pdb*'-file) is read in MatCalc – this is the third type of the databases provided with MatCalc, next to the thermodynamic ('*.tdb*'-files) and diffusion ('*.**ddb*'-files) ones.

Upon reading the database, the molar volumes (a reciprocal of the molar density) are loaded for all the phases. These variables are located in the '*mass/volume/density*' section.

The '*VP$Phase*' variables represent the volume of the phase in the system. The '*V*' variable represents the volume of the whole system. Hence, the volume fraction can be calculated as the ratio of '*VP$Phase*' to '*V*' variable, e.g. '*VP$FCC_A1/V*'.