MTDATA – Phase Diagram Software from the National Physical Laboratory

 

 

 

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Gplot

Introduction

The GPLOT module allows thermodynamic data for binary systems (ie for systems containing two components) to be plotted and tabulated for fixed temperatures but as a function of composition. The GPLOT module allows the user to evaluate data in this way for a wide variety of phases such as alloys, molten salts, slags, interstitials, mattes and pure stoichiometric substances. A wide range of different thermodynamic quantities can be plotted. Data for the calculations are retrieved directly from thermodynamce databases or from file created in advance through use of the ACCESS module. Experimental data may be superimposed onto the calculated diagram. Graphical output is sent both to the screen and to a file so that the contents can be routed to a local plotter, either from within the program or by using operating system commands. Data for each solution phase (ie those which exist over a range of homogeneity) are plotted with a different line style. Data for stoichiometric phases are indicated by a symbol consisting of a cross within a circle.

Brief summary of commands

DEFINE allows the user to name the datafile from which the data are to be retrieved or to define the system to be studied in terms of the two components, in which case the data are retrieved from a named database. The datafile must be in the MTDATA Multiphase format (file extension ".mpi") and should preferably have been retrieved in advance by means of the ACCESS module.

LIST displays the current definition of the problem in terms of:

(a) the status of the elements, components, substances, unaries or phases present
(b) the pressure and the temperature for the calculations as set by the user.

CLASSIFY allows the status of individual phases or substances to be classified as NORMAL (present) or ABSENT from the calculation. The number of miscibility gaps potentially present may also be specified if they are to be taken into account in the calculation.

SET allows the user to specify the pressure and temperature for the calculations.

STEP allows the user to specify the range of compositions and the step size to be used for the calculations.

COMPUTE initiates the computation and plotting of the thermodynamic functions within the range of compositions specified. In its simplest form, entering COMPUTE ! (with no parameters) will initiate the calculations. However, this command has various parameters that allow the equilibrium calculations to be controlled. However the default setting for these parameters will be sufficient for most calculations. Output from the calculations is sent to a results file (defined using DEFINE OUTPUT_DATA) and to the screen (except when the PRINT_LEVEL is set to GRAPHICS). If no results file has been defined the the default results file "def.mpr" is used. Once the calculations have been completed, a graph may be produced using the PLOT command.

PLOT This command plots the thermodynamic function on the y-axis (selected using the ORDINATE_SET) against composition on the x-axis. The executive command is simply PLOT ! and entry of this followed by a carriage return (to clear the screen) will plot the graph. Output from PLOT can be sent to the screen or to a file (or both) using the OUTPUT parameter (the contents of the file can then be sent to a hard copy device). Other parameters allow a previously compiled experimental file to be defined. The contents of the file will be superimposed automatically onto the graph. Finally the size of the graph can be specified using the FRAME_SIZE parameter.

ABSCISSA_SET allows the user to set the range of compositions to be plotted on the x-axis of the graph produced using PLOT. Compositions are expressed in terms of the mole fraction of the second component. The range of compositions to be plotted can be specified usinf the LIMITS parameter.

ORDINATE_SET allows the user to set which thermodynamic function is to be to be plotted on the x-axis of the graph produced using PLOT. Either the thermodynamic function of the whole system can be plotted, or (by specifying a component name), the partial molar thermodynamic function of one of the components.

RETURN takes the user out of GPLOT back to the module level.

LASER sends a copy of any diagrams plotted on the screen to a local plotting device if available.

<"Macro name"> runs a macro taken from a file. The name of the file should be entered in quotes. Commands can also be passed through to the operating system by prefixing them with a $ (dollar sign). The dollar sign and operating system command should be entered within quotes.

Further Information

A gentle introduction gentle introduction to using the options available in GPLOT contains annotated examples, each directed towards achieving a particular outcome, showing typical combination of commands which would be necessary to achieve that end.

A simple summary of the commands available can also be used as an index to obtain more detailed help about each command.

 

Updated 30 June 2010