MTDATA – Phase Diagram Software from the National Physical Laboratory







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The calculation of phase boundaries of triangular sections through multicomponent systems at fixed temperatures and pressures

This application is used for calculating horizontal sections through multicomponent phase diagrams for fixed temperatures and pressures but with varying (constrained) compositions based on a triangular section. Graphical output is produced as the calculations proceed showing the phase boundaries calculated by MTDATA. Two different algorithms for calculating these sections are available within MTDATA. In the first algorithm (TRISECT), the graph displayed consists of a series of discrete points ie not joined up. Options are available to perform more calculations within a given area and to label individual phase fields. Following the calculations it is possible to arrange for a graph to be plotted with all the calculated points joined up.

In the second algorithm (NEW_TRISECT), the calculation follows each line on the phase diagram across the phase diagram using the concept of zero phase fraction. Again options are available to label individual phase fields.

Before asking for the isopleth to be calculated it is necessary to define a datafile, to classify any phases required to be absent or identified as giving rise to miscibility gaps and to specify the temperature and pressure. Also the range of compositions must be defined by setting three compositon groups and specifying the number of compositions to be examined between them. All this can be set up using the normal APPLICATION commands within MTDATA.

The application is designed for a multicomponent system (ie with at least three components). The following example, however, is for a three component system. In this case the ternary section is identical to an ordinary ternary diagram. To calculate sections in higher order systems it is necessary simply to add more components to the composition groups.

set 'A' 0.9998 0.0001 0.0001 !
set 'B' 0.0001 0.9998 0.0001 !
set 'C' 0.0001 0.0001 0.9998 !

The density of calculations is set through use of the user variable "number_of_steps".

set user_v(number_of_steps) 30 !

and the corners of the diagram assigned to the composition groups.

set user_v(group_lower_left) 'A' !
set user_v(group_top) 'B' !
set user_v(group_lower_right) 'C' !

Extra calculations to be carried out in regions where phase boundaries meet. This can be turned off using the "refine" user variable. By default this variable is set to 1. However if extra calculations are not required the change can be initiated with:

set user_v(refine) = 0 !


Updated 7 May 2010