MTDATA – Phase Diagram Software from the National Physical Laboratory

 

 

 

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ORDINATE

Function:

allows the user to choose what is to be plotted as ordinate, the range of values plotted and whether a logarithmic, reciprocal or linear scale is to be used. The choice of variable to be plotted will normally entail further decisions by the user in order to select the particular substances, phases or components for which curves are to be plotted. If no graphics results file has been defined that corresponding to the most recent MULTIPHASE graphics calculation will be automatically loaded.

Parameters:

n_(amount)

mass

x_(mole_fraction)

w_(weight fraction)

molality

partial_pressure

component_distrib.

activity_(notional)

chemical_potential

component_activity

focus_on_component

pressure

volume

temperature

Eh

Ph

enthalpy

gibbs_energy

entropy

heat_capacity

user_variable

reciprocal

log_scale

limits

+

*

Defaults:

n_(amount) = substance

log_scale = no

limits = full range of calculation

focus_on_component = none

Examples:

ordinate n = substance !

ordinate n = substance(spinel) !

ordinate n = substance(4) !

ordinate mass = phase(liquid) !

ordinate x = su(gas) !

ordinate w = phases !

ordinate molality = substance !

ordinate partial_pressure = substance(27) !

ordinate component_distrib. = Component(h2o) !

ordinate component_distrib. = In_phase(liquid) !

ordinate activity_notional = phase(cr2o3) !

ordinate component_activity = component(cu) !

ordinate chemical_potential = component(ni) !

ordinate gibbs_energy = linear_reference !

ordinate volume = system !

ordinate pressure = system !

ordinate focus_on_component = component(br) !

ordinate log_scale = yes !

ordinate limits = 0.7 3.2 !

ordinate heat_capacity = recalculate !

Parameter values:

N_(AMOUNT)

takes the values COMPONENT(*)/PHASE(*)/SUBSTANCE(*)

This parameter should be selected in order to plot amounts in terms of numbers of moles. To plot the amounts of individual components, phases or substances the appropriate value (COMPONENT, PHASE or SUBSTANCE) should be subscripted (in brackets) by the NAME of the chosen component, the NAME of the chosen phase or the NUMBER of the chosen substance respectively eg "n=c(CaO)", "n=p(melilite)" or "n=su(4)". If no subscript is given the amounts of all components, phases or substances in the system will be plotted eg "n=comp", "n=ph" or "n=su". To plot the amounts of all substances within a given phase the value SUBSTANCE should be subscripted by the appropriate phase NAME eg "n=sub(liquid)". To plot the ratio of the amounts of substances 2 and 5 the value substance should be subscripted by the substance numbers separated by a colon eg "n=sub(2:5)". To plot the ratio of the amounts of two components in a particular phase (eg CaO and SiO2 in the LIQUID phase) the value component should be subscripted by the component names separated by a colon followed by a comma ane then the phase name eg "n=comp(CaO:SiO2,LIQUID)". See also FOCUS_ON_COMPONENT.

MASS

takes the values COMPONENT(*)/PHASE(*)/SUBSTANCE(*)

This parameter should be selected in order to plot amounts in terms of mass. To plot the masses of individual components, phases or substances the appropriate value (COMPONENT, PHASE or SUBSTANCE) should be subscripted (in brackets) by the NAME of the chosen component, the NAME of the chosen phase or the NUMBER of the chosen substance respectively eg "ma=c(CaO)", "ma=p(melilite)" or "ma=su(4)". If no subscript is given the masses of all components, phases or substances in the system will be plotted eg "ma=comp", "ma=ph" or "ma=su". To plot the masses of all substances within a given phase the value SUBSTANCE should be subscripted by the appropriate phase NAME eg "mas=sub(liquid)". To plot the ratio of the masses of substances 2 and 5 the value substance should be subscripted by the substance numbers separated by a colon eg "mas=sub(2:5)". To plot the ratio of the masses of two components in a particular phase (eg CaO and SiO2 in the LIQUID phase) the value component should be subscripted by the component names separated by a colon followed by a comma ane then the phase name eg "mas=comp(CaO:SiO2,LIQUID)". See also FOCUS_ON_COMPONENT.

X_(MOLE_FRACTION)

takes the value SUBSTANCE(*)

This parameter should be selected in order to plot the mole fraction of a particular substance (species) within its phase. The value SUBSTANCE should be subscripted (in brackets) by the number of the chosen substance and not its name eg "x=su(21)". Note that the number required is the overall species number and not the number of the species within the particular phase. The mole fractions of ALL species within a particular phase can be plotted by entering the phase name as a subscript instead of a number eg "x=S(gas)". See also FOCUS_ON_COMPONENT and COMPONENT_DISTRIB.

W_(WEIGHT_FRACTION)

takes the values SUBSTANCE(*)

This parameter should be selected in order to plot the mass fraction of a particular substance (species) within its phase. The value SUBSTANCE should be subscripted (in brackets) by the number of the chosen substance and not its name eg "w=su(11)". The mass fractions of ALL species within a particular phase can be plotted by entering the phase name as a subscript instead of a number eg "w=su(bcc)". See also FOCUS_ON_COMPONENT and COMPONENT_DISTRIB.

MOLALITY

takes the values SUBSTANCE(*)

This parameter should be selected in order to plot the molality of a particular substance (species) in aqueous solution. The value SUBSTANCE should be subscripted (in brackets) by the number of the chosen substance and not its name eg "mol=su(5)". If no subscript is given then the molalities of ALL species in aqueous solution will be plotted eg "molal=sub". See also FOCUS_ON_COMPONENT.

PARTIAL_PRESSURE

takes the values SUBSTANCE(*)

This parameter should be selected in order to plot the partial pressure (pressure/standard state pressure) of all or individual gaseous species. A single species can be selected by subscripting (in brackets) the value SUBSTANCE by the appropriate substance number eg "part=su(5)". Note that the substance name cannot be used. If no subscript is given then the partial pressures of all gaseous species will be plotted eg "par=sub". See also FOCUS_ON_COMPONENT.

COMPONENT_DISTRIB

takes the values COMPONENT(*)/MASS_IN_PHASE(*)/MOLES_IN_PHASE(*)/AQUEOUS_MOLALITY(*)

This parameter should be selected in order to investigate the distribution of a chosen component between phases or the distribution of all components within a particular phase (this latter in either mass or mole terms). If the value COMPONENT is subscripted (in brackets) by a valid component name then the fraction of the total (system) amount of this component residing in each phase will be plotted eg "com_dist=c(Fe)". (Note that the curves obtained would be identical whether calculated in mass or mole terms). To plot the mass fraction of each component within a particular phase the value MASS_IN_PHASE should be selected and subscripted by the appropriate phase name eg "co_d=mas(spinel)". If mole fractions are required then MOLES_IN_PHASE should be chosen instead eg "co_dis=mol(liquid)".

If the value AQUEOUS_MOLALITY is chosen the resultant plot is for all components if not subscripted or for a single component if subscripted with a component name.

ACTIVITY_NOTIONAL

takes the values PHASE(*)/ALL

This parameter should be selected in order to plot the actual or notional activity of a stoichiometric phase. The value PHASE should be subscripted (in brackets) by the appropriate phase name eg "act=ph(wollastonite)". To plot the activity/notional activity of all suitable phases the value ALL should be entered eg "activ=all". Note that the activities obtained in these plots are independent of any reference phases CLASSIFY'd for the components. The closer the notional activity of a phase is to unity the closer that phase is to being stable at equilibrium. The activity of a phase stable at equilibrium is unity.

COMPONENT_ACTIVITY

takes the value COMPONENT(*)

This parameter should be selected in order to plot the activity of a particular component in the system under consideration. The value COMPONENT should be subscripted (in brackets) by the chosen component name eg "c_a=c(KCl)". If no subscript is given the activities of all components will be plotted eg "c_a=c". The numbers obtained depend upon the choice of reference phase for each component. This choice may be modified before starting a MULTIPHASE calculation by means of the CLASSIFY command.

CHEMICAL_POTENTIAL

takes the values SUBSTANCE(*)

This parameter should be selected in order to plot the partial molar Gibbs energy of a particular substance (species). The value SUBSTANCE should be subscripted (in brackets) by the number of the chosen substance and not its name eg "ch_p=su(7)". Partial molar Gibbs energies can be plotted for all species within a particular phase by entering the phase name as a subscript instead of a number eg "chem=su(liquid)". Note that the chemical potential is defined relative to the reference phases of the components. If a reference phase other than the default is required, this must be CLASSIFIED before the calculations are made. In this case the reference temperature is that of the calculation. Otherwise the partial value relative Hser is plotted, ie the reference state is normally that of the pure elements in the phases in which they are stable at 298.15 K and the reference temperature is also 298.15 K.

GIBBS_ENERGY

takes the values SYSTEM/LINEAR_REFERENCE/PHASE(*)

The Gibbs energy of the system as calculated can be plotted by entry of "gibbs=sys". The values obtained depend on the reference phases CLASSIFIED prior to the calculation.

For the purpose of detecting curvature in the Gibbs energy as a function of composition (for example in the search for miscibility gaps), particularly in cases where this is obscured by a very large linear change in Gibbs energy, the linear part can be subtracted off by entering "gibbs=linear_reference". The function plotted is:

G - GA(1-x) - GBx

where the plot runs from condition A to condition B and x is the fraction of the vector from the abscissa value at A to that at B.

The contribution to the total Gibbs energy made by a particular phase can be plotted by entering "gibbs=phase(<name>)". If the value phase is not subscripted by a name then the contribution made by all phases individually will be plotted.

PRESSURE

takes the value SYSTEM

the overall pressure of the system can be plotted by entry of "pre=system".

VOLUME

takes the value SYSTEM

the volume of the system, normally that of the gas phase, can be plotted by entry of "vol=system".

TEMPERATURE

takes the value SYSTEM

ENTHALPY

takes the values SYSTEM/LINEAR_REFERENCE/RECALCULATE

In order to obtain a plot of the enthalpy of the system under consideration the user should enter:

ordinate enthalpy system !

In addition to the SYSTEM value a value of RECALCULATE may be chosen. This results from a numerical differentiation of the Gibbs energy and in general should give the same results to SYSTEM. If the results from SYSTEM and RECALCULATE differ the RECALCULATEd values should be used.

It is possible that a large linear change in enthalpy across a range of composition might mask more subtle features of interest. In order to subtract off the linear part of the change in enthalpy across the abscissa range under consideration, and so make such features more readily apparent, the user should enter:

ord enth linear_reference !

HEAT_CAPACITY

takes the value SYSTEM

In order to obtain a plot of the heat capacity of the system under consideration, the user should enter:

ordinate heat_capacity system !

The resulting Cp values are obtained numerically from the Gibbs energy and are therefore only available when temperature is the stepped variable.

Because of the numerical nature of the derivation of Cp a plot may show impossible negative values. These arise from two causes. Either there is an un-classified miscibility gap or there is a discontinuity in the Gibbs energy functions used. In the latter case reducing the temperature step or using a non-rounded temperature step value may help.

ENTROPY

takes the values SYSTEM/LINEAR_REFERENCE/RECALCULATE

In order to obtain a plot of the entropy of the system under consideration the user should enter:

ordinate entropy system !

In addition to the SYSTEM value a value of RECALCULATE may be chosen. This results from a numerical differentiation of the Gibbs energy and in general should give the same results to SYSTEM. If the results from SYSTEM and RECALCULATE differ the RECALCULATEd values should be used.

Eh

takes the values H/+_ION_MOLALITY

In order to plot eH as ordinate the user should enter:

ordinate eH H/+_ION_MOLALITY !

The system under consideration must include an AQUEOUS phase containing the species H/+<aq> and a GAS phase containing the species H2<g>. The eH values are calculated from the H/+<aq> molality and the H2<g> partial pressure as follows:

Eh = -ln10 RT ( (log10 p(H2<g>))/2 + pH )/F

pH = -log10 m(H/+<aq>)

Ph

takes the values H/+_ION_MOLALITY

In order to obtain a plot of the pH of the system under consideration (which must include an AQUEOUS phase containing the species H/+<aq>) the user should enter:

ordinate pH H/+_ION_MOLALITY !

The pH values are calculated from the H/+ ion molality in the AQUEOUS phase as follows:

pH = -log10 m(H/+<aq>)

USER_VARIABLE

takes the value of any user variable defined at the time of the calculation to produce the current graphics (".gph") file can be selected as ordinate by entering the appropriate variable name at the WHICH USER_VARIABLE ? prompt. For example

ordinate user_variable viscosity !

ord us_v batch_number !

To plot out a series of user variables beginning with the same set of characters (eg MASS_PHASE_1, MASS_PHASE_2, MASS_PHASE_3 etc) the common characters should be entered in brackets after the parameter ALL. For example

ordinate user_variable all(mass) !

If the parameter ALL is entered without giving a subscript in brackets then all user variables will be plotted.

FOCUS_ON_COMPONENT

takes the values COMPONENT(*)/NONE

This parameter should be selected if the user is interested only in those phases or substances containing a particular component. The name of that component should be given as a subscript (in brackets) to the value COMPONENT eg "foc_on=c(S)". Curves relating to phases or substances which do not contain the chosen component will then be suppressed in all plots until the focussing is cancelled. This is done by entering the option NONE eg "fo=none".

LOG_SCALE

takes the values YES/NO

enables the user to choose between a logarithmic or linear scale. The default is linear.

RECIPROCAL

takes the values YES/NO

Enables the user to plot the reciprocal of the chosen ordinate variable rather than the variable itself. This is achieved by selecting the value YES. The default value is NO. Note that selecting a RECIPROCAL scale for the ordinate will cancel any previously selected LOG_SCALE.

+

takes the values <number> or NONE

This parameter is used to offset all ORDINATE values by a constant. The constant may be positive or negative and should be specified following the + parameter but seperated from it by a space. For example:

ordinate enthalpy system + 100000 !

ordinate temperature system + ­273.15 !

The units in which the constant is specified are assumed to be the same as the ORDINATE variable being plotted. The value NONE is used to cancel the offsetting of ORDINATE values.

If both an offset and a scale factor (see *) are specified the offset value is NOT multiplied by the scale factor.

*

takes the values <number> or NONE

This parameter is used to multiply all ORDINATE values by a constant scale factor. This factor may be positive or negative and should be specified following the * parameter but seperated from it by a space. For example:

ordinate w sub(20) * 100 !

would cause weight percents to be plotted instead of weight fractions. The value NONE should be selected in order to cancel the application of a scale factor to ORDINATE values.

If both a scale factor and an offset (see +) are specified the offset value is NOT multiplied by the scale factor.

LIMITS

takes the values AUTO/<MINIMUM,MAXIMUM>

This parameter should be selected if the user wishes to specify a particular range for the ordinate scale. Both the maximum and minimum values required must be entered although the order is not important eg "limit=­15 ­3". If the value AUTO is given then the limits for the ordinate scale are calculated automatically eg "limit=auto". That is to say they are set equal to the maximum and minimum values of the property to be plotted. This happens by default if no other limits have been set.

General comments:

The substance numbers used when defining the ORDINATE and ABSCISSA are selected with respect to a list of substances stored in the ".gph" file and not those defined by the current ".mpi" file.

 

Updated 7 May 2010