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.
The equilibrium state for which calculations are to be performed
is defined by specifying the temperature, pressure or volume,
and the quantity of substance. This quantity may be specified either by
fixing the overall amount of each component in the system, i.e.
by specifying amount of reactants, or by specifying the amounts
of substances present at equilibrium in terms of variables such
as mole fraction in a phase, partial pressure and molality, or
as a combination of the two.
types of calculation can be performed. STAGE
1 uses true Gibbs energy minimisation and gives very reliable
results without the need of an initial guess of the equilibrium
condition by the user. STAGE 2 also achieves Gibbs energy minimisation
but does this by equalising the chemical potentials of the components
between the phases. STAGE 2 is used when it is necessary to calculate
the amounts of substances less than 10-6 mol.
cases STAGE 1 is normally used to provide an initial guess
for STAGE 2 but it is also possible to use a previous result for
a closely related calculation.
for the calculations are retrieved either from
specified databases or from a datafile prepared in advance. This
datafile would normally have been generated from the databases
by means of the ACCESS module. The databases will
on the installation; those that may be available include:
Recommended data for the elements
Scientific Group Thermodata Europe database
Scientific Group Thermodata Europe solution
NPL Database for salt systems
which may be added private or specialised databases
managed by individual users or groups.
can be produced in tabular or graphical forms
and sent both to the screen and to a file and hence to a printer.
headings in the tabular output are self-explanatory,
but the following points are worth noting:
the mole fraction/partial pressure/notional activity
column indicates the mole fraction or partial pressure only if
the relevant phase is present at equilibrium. Otherwise, the values
in this column give an indication of how unstable the phase is:
numbers close to unity suggest that slight changes in conditions
could result in those substances being present in the equilibrium
the heading "STAGE 2 RESULTS" indicates
that this calculation has included substances in amounts less
than about 10-6 mol.
graphical output is required, the results of
a series of calculations are written to a file, with the extension .gph,
and the ORDINATE, ABSCISSA and PLOT
commands are used to enable the results to be plotted in many
types of tabulation may also be obtained.
Brief summary of commands
allows the user to name the datafile from which the data will
be retrieved or to define the system retrieving data from a named
database or databases. The datafile would normally have been prepared
by means of the ACCESS module.
LIST displays the
current definition of the problem in terms of:
the status of the elements, components, substances
and phases present
(b) initial and/or equilibrium
quantities of components
SET by the user
(c) temperature and
pressure/volume set by the user.
the status of individual components, phases and substances to
be classified as NORMAL (present), ABSENT or FREE for the purposes
of a subsequent calculation. The reference phase for individual
or all components can be selected. The number of miscibility gaps
potentially present may also be specified. A computational parameter
DELTA required to deal with FREE components can be fixed in this
SET allows the user
to specify the temperature, pressure/volume, and quantities within
the system. Quantities may be defined in terms of either total
amounts or mass of each component in the system or amounts of
certain substances present at equilibrium. Equilibrium amounts
may be specified in terms of moles, kilograms, mole fraction,
partial pressure or molality. A special use of SET
name and define the end points (GROUPS) of a stepped sequence
in overall composition.
STEP is used mainly
in the preparation of graphs. Most of the variables that can be
set may be stepped. There are two modes of operation. The user
enters either the start, finish and step interval, or the names
of the start and finish composition groups as defined by the SET
command and the number of points to be calculated.
the computation of currently specified equilibria, at all temperatures
specified in SET TEMPERATURE. The STAGES used and
of initiating the calculation can be changed. The type of tabular
output can be varied to provide more or less detail. Alternatively
the output can be sent to a graphics file.
ORDINATE is used
to select which, out of many possible variables, is plotted as
ordinate, to select log or non log scales and their range.
ABSCISSA is used
to control which variable is plotted as abscissa. This does not
need to be the originally stepped variable. Log or non log scales
may be chosen and their range controlled.
PLOT is used to retrieve
a previously calculated graphics file for plotting, to change
the physical characteristics of the plot and to initiate the plot
itself. Additionally the selected variables may be output in tabular
form and experimental data superimposed on a MULTIPHASE
the user to control the units of temperature and pressure used
in the graphical output.
a copy of any diagrams plotted on the screen to a local plotting
device if available.
takes the user out of MULTIPHASE back to the module
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
introduction to using
the options available in MULTIPHASE contains
examples, each directed towards achieving a particular outcome
and shows typical combination of commands which would be necessary
to achieve that end.
summary of the commands
available can also be used as an index to obtain more detailed
help about each command.