MTDATA – Phase Diagram Software from the National Physical Laboratory







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Overview of MTDATA

MTDATA comprises a suite of related modules which retrieve thermodynamic data from databases and perform specified calculations on the data. The databases may be provided with the package or maintained by the user. A summary of the functions of some of the modules is given below.

An important feature of MTDATA is the maintenance of a system of traceability that is compatible with total quality management. For this purpose a log is maintained of all user interaction.

Words such as element, component, substance, compound, species, condensed, phase and solution will be encountered frequently. For detailed understanding of these terms please consult the glossary and information about databases, definitions and models.

It is possible to assign values to a range of settings that apply across the whole of MTDATA and affect a number of ways in which MTDATA appears or the accuracy of the calculations. These are called "Configuration Variables" and are assigned through use of "[" followed by the appropriate variable name. A list of the most important Configuration Variables can be obtained here.


The MTDATA package includes a number of utilities for creating, loading and listing databases. Facilities are also incorporated for personalising access to particular databases and for customising graphics output. The box shows, as an example, part of a source datafile to be incorporated into a database by UTILITY.

Cr/+3,Ni/+2:Va<LIQUID*> E/J
298.150 2
­1.2760000E+03 ­5.3873000E+00
2.6990000E+03 0.0000000E+00
0 0


The ACCESS module is designed to be used as a data retrieval system for MULTIPHASE, GPLOT, BINARY, TERNARY, APPLICATION and COPLOT, with which it shares common features. The components, which may be elements, compounds or charged species, are entered and the databases are searched for all the substances which might be present in the system at equilibrium. In a large system this could run to many hundreds of substances, many of which may not be very relevant to a particular application and may therefore be excluded. ACCESS allows the user to remove these substances from consideration completely, and to choose from which databases the data for the remaining substances are to be retrieved on an individual basis. There may also be a need to select from alternative models for solution phases. Once the data for the system have been edited into a form which satisfies the user, they can be saved to a file which can then be read by the calculation modules for subsequent processing.

ACCESS OPTION ? define system 'Fe,Cr,Ni,C' source sgsol !
SEARCHING DATABASE(S) : SGSOL - SGTE Solution Database 3.0 ­ 2/2/93

ACCESS OPTION ? list sys phases ! The list has been greatly abbreviated

3          LIQUID        NORMAL     REDLICH-KISTER
4          GAS           NORMAL     IDEAL GAS
5          BCC_A2:1:3    NORMAL     SUBLATTICE
7          FCC_A1:1:1    NORMAL     SUBLATTICE
8          HCP_A3:1:.5   NORMAL     SUBLATTICE
10         M3C2:3:2      NORMAL     SUBLATTICE
11         M7C3:7:3      NORMAL     SUBLATTICE
12         M23C6:20:3:6  NORMAL     SUBLATTICE
22         SIGMA:8:4:18  NORMAL     SUBLATTICE


MULTIPHASE is a module for the calculation of multiphase, multicomponent equilibria. Phases may include alloys, molten salts, gases, aqueous solutions, slags, mattes and pure stoichiometric substances in combination. Calculations may be made at constant pressure or volume with a fixed system composition; alternatively, constraints may be placed on the equilibrium system in terms of variables such as mole fraction in a phase, partial pressure and molality. Data for the calculations are read either from specified databases, or from a previously prepared datafile; this may be precompiled by using the ACCESS module.

Output, in the form of tabulated equilibrium amounts and mole fractions of each of the substances present at equilibrium, for each of the temperatures specified, is sent both to the terminal and to a file. Graphical output can be invoked from within MULTIPHASE in order to plot the amounts, mole fractions, partial pressures, component partition between phases and activities as a function of stepped or dependent variables. Results may be presented in mole or weight terms.


The main function of THERMOTAB is to act as the user interface to the internal database management system of MTDATA. At present all data can be inspected but calculations involving equations are available only for pure substances, gases and dilute aqueous species. The UTILITY module should be used for data management for solution phases. UNARY, GPLOT and MULTIPHASE can be used to obtain tabulations and plots.

Fe3O4 + 3 H/+<aq> = 1/2 O2<g> + 3 Fe(OH)/+<aq>

T       Delta Cp  Delta H      Delta S   Delta G    Beta
K       J/K mol   J/mol        J/K mol   J/mol      -DG/RTln10

298.15  13.277   1.48680E+05   133.27   1.88413E+05 ­33.008
373.15  10.914   1.49606E+05   130.49   1.98297E+05 ­27.758
473.15   0.21007 1.50253E+05   128.90   2.11243E+05 ­23.320
573.15  ­22.630   1.49241E+05   130.77   2.24193E+05 ­20.432

THERMOTAB provides output of the Thermodynamic functions Cp, S, G, H, Phi = -(G-H)/T and Beta = -G/RTln10, over a range of temperatures specified by the user, for pure substances or for chemical reactions between pure substances. The output can be produced in tabular or graphical form, and may be displayed on the screen or saved to a file. Hard copy can be obtained by routing the file to a local or networked printer. The module also allows data to be copied from the reference databases provided, modified by the user, and used to compile private or specialised databases.


UNARY is used in data development, for example the provision of data for a liquid below the melting temperature of the pure substance. It is also useful in the graphical comparison of data from different sources or different phases.


GPLOT is used mainly for plotting but also for tabulating thermodynamic functions of phases of all types. The main application lies in the development of data for binary systems which can include systems between compounds.


The BINARY module is used for the calculation and plotting of binary phase diagrams, mainly as an aid to data assessment and validation. The data are retrieved in the same way as with the ACCESS module. The user sets up the calculation by specifying the temperature range and he may subsequently select parts of the diagram for closer inspection. Labelling of single or two phase regions is very simple. Key information on phase boundaries is given numerically and hard copy can readily be obtained.


The TERNARY module is used to plot ternary phase diagrams. Data may be retrieved directly databases or from a datafile compiled using the ACCESS module. The user may optionally specify a starting point on the ternary diagram for the calculations to begin; thereafter the computations required for the graph to be plotted can be entirely automatic. The diagram can be in weight or mole fraction. Areas can readily be labelled and diagrams reorientated.


APPLICATION allows the core phase equilibrium calculation facility of MTDATA to be used for a variety of purposes including calculating arbitrary sections through systems, finding the temperatures of phase transitions for individual compositions and the preparation of Scheil plots. The facility is provided for users to develop their own process modelling software for linking to MTDATA.


COPLOT is used for plotting predominance area diagrams (also called Pourbaix and phase stability diagrams) for systems of stoichiometric substances and up to 10 components. The potential of two of the components are the independent axis variables, others may have fixed potentials and at least one component is specified by amount. The output comprises a plot showing the fate of this or these component(s) as a function of the remainder. This type of plot is much used by corrosion scientists and hydrometallurgists.


FITANDPLOT is used for fitting compiled thermodynamic data to user defined mathematical functions. It incorporates checking for typing errors and can also be used for converting data already in the form of an equation to a different function.


The ASSESSMENT module provides tools to help in the task of deriving values for thermodynamic model parameters, which, when used as a basis for phase equilibrium calculations, give the best possible representation of a collection of experimental measurements obtained for a particular chemical system. This overall task of gathering data and generating values for parameters is referred to as data assessment or sometimes critical assessment since it involves comparing data of many different types, from many different sources, obtained using many different experimental techniques. The specific task of generating model parameters appropriate to a set of experimental data is called optimisation.


Updated 26 May 2010