MTDATA – Phase Diagram Software from the National Physical Laboratory

 

 

 

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COMPUTE

Function:

initiates the computation of the ternary phase diagram for the temperature and pressure or volume specified in the SET command.

Parameters:

print_level

ternary_step_size

triangle_fill

Defaults:

print_level = none

ternary_step = 0.02

triangle_fill = dots

Examples:

compute ter = 0.03 print = file !

Parameter values:

PRINT

takes the values NONE/ FILE/ MOLE_FRACTION/ WEIGHT_FRACTION

NONE provides no tabular output of results.

FILE sends standard MULTIPHASE output to a file which can be examined later. For an example and description of this output please see information about MULTIPHASE.

TERNARY_STEP_SIZE

takes the value of <real number>

The step size is a measure of spacing between calculated tie lines. A larger number than the default will give a diagram with fewer tie lines and the phase boundaries plotted with less accuracy. A smaller number than the default will have the opposite effect.

TRIANGLE_FILL

takes the value NONE/ DOTS/ SHADED

The parameter SHADED is appropriate for POSTSCRIPT output only.

Operation of the graphics interface

The command style within the COMPUTE option is different from that in the rest of MTDATA because of the way in which the interaction between the host computer and the graphics terminal is handled. The facilities provided are:

(a) Entry to the plotting option : COMPUTE ! <CR>

This automatically switches to graphics mode provided a suitable terminal, emulator or PC screen is being used. The ternary axes are drawn, calibrated and labelled and, if initial compositions have not already been set, the crosswires or other graphics cursor appears. These are normally controlled by the cursor keys or a mouse.

(b) Drawing the ternary diagram

Before it can begin the calculation of the diagram, the program requires an initial composition which it obtains either via the SET command or by reading the position of the graphics cursor. Therefore, in the latter case before issuing any of the following commands, the graphics cursor must be positioned in an area of the graph which you suspect to be a two or three phase region.

P or p   draws the complete diagram, but does not define the phase boundaries by fitting the tie-line ends.
F or f    draws the complete diagram, fitting the boundaries to the tie-line ends.
L or l    identifies the phases in equilibrium for the composition specified by the cursor position. On depressing a second time after reappearance of the cursor the phase names are printed at the cursor position. If desired the cursor may be moved from its original position and the phase labels written out at a different location of the screen. Labels should only be added after plotting of the whole diagram is complete.

any key other then than A, P, F or L will perform a single calculation with the following results:

           Phases in Equilibrium    Result
                          one                point
                          two                tie line
                          three              triangular  boundary of the three phase region

This feature is particularly useful in searching a ternary diagram for a suitable starting point when you have little initial knowledge of the system.

For use of both P and F, the program starts at the composition specified by either the SET command or the graphics cursor, and continues to calculate boundaries for two and three phase regions, as long as they are contiguous. The separation of two successive tie lines is governed by the TERNARY_STEP parameter. If there are other two or three phase regions not topologically linked to the phases currently being calculated, then the program has no way of "stepping over" and continuing the calculation. If the calculation stops, leaving a suspiciously large area of single-phase region, then it may be advisable to move the crosswires into it and continue to examine the phase equilibria manually in a systematic fashion, to verify the absence of two and three-phase regions within it.

When calculating phase diagrams using the TERNARY module it is strongly recommended that the user has calculated previously the three binary sub-systems perhaps using the BINARY module. Inspection of the binary phase diagrams may indicate areas in the ternary diagram not yet completed.

While calculation is in progress, the graphics cursor disappears; it reappears when the calculation has finished and another command can be entered.

(c) Exit from the plotting option: A <CR>

General comments:

Output may also be sent to the systems scratch file PLOT.OUT depending on the HCPY parameter set in the MTSIGNON.TXT initialisation file. Hard copy plots can be obtained by using the command LASER which copies the contents of this file to the local plotting device.

 

Updated 2 July 2010