MTDATA – Phase Diagram Software from the National Physical Laboratory

 

 

 

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ABSCISSA

Function:

allows the user to choose what is to be plotted as abscissa, the range of values plotted and whether a logarithmic, reciprocal or linear scale is used. The choice of variable to be plotted as abscissa is limited by the choice of variables in the original calculation and will normally entail further decisions. In choosing anything other than the originally stepped variable as abscissa, there is a risk of loss of information and the possibility that the chosen variable may be dependent on factors not apparent from the information given to the right of each graph. It is advised that at least one plot is made with the default variable as abscissa.

Parameters:

default

n_(amount)

mass

x_(mole fraction)

w_(weight fraction)

molality

partial_pressure

pressure

component_activity

component_distrib.

volume

temperature

log_scale

limits

reciprocal

user_variable

Eh

Ph

+

*

Defaults:

default

log_scale = no

limits = full range stepped in calculation

Examples:

abscissa n = component(NaCl) !

abscissa Mass = phase(liquid) !

abscissa X = su(4) !

abscissa W = su(4) !

abscissa Molality = substance(15) !

abscissa Partial_pressure = substance(27) !

abscissa Volume = system !

abscissa Pressure = system !

abscissa Log_scale = yes !

abscissa Limits = 0.7 3.2 !

Parameter values:

N_(AMOUNT)

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

This parameter can be used to select for plotting as abscissa the amount of an individual component, phase or substance expressed in terms of moles. 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)".

MASS

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

This parameter can be used to select for plotting as abscissa the amount of an individual component, phase or substance expressed in terms of mass. 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)", "mas=p(melilite)" or "ma=su(4)".

X_(MOLE_FRACTION)

takes the value SUBSTANCE(*)

This parameter can be used to select for plotting as abscissa the mole fraction of a particular substance within its own phase. The value SUBSTANCE should be subscripted (in brackets) by the number of the chosen substance and not its name eg "x=su(2)". Note that the number required is the overall species number and not the number of the species within the particular phase.

W_(WEIGHT_FRACTION)

takes the value SUBSTANCE(*)

This parameter can be used to select for plotting as abscissa the weight fraction of a particular substance within its own phase. The value SUBSTANCE should be subscripted (in brackets) by the number of the chosen substance and not its name eg "w=su(21)".

MOLALITY

takes the value SUBSTANCE(*)

This parameter can be used to select the molality of a particular substance in the aqueous phase for plotting as abscissa. The value SUBSTANCE should be subscripted (in brackets) by the number of the chosen substance and not its name eg "mol=su(2)".

COMPONENT_ACTIVITY

takes the value COMPONENT(*)

This parameter can be used to select the activity of a particular component in the system under consideration as abscissa. The value COMPONENT should be subscripted (in brackets) by the chosen component name eg "c_a=c(KCl)". 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.

COMPONENT_DISTRIB

takes the value AQUEOUS_MOLALITY(*)

This parameter should be selected in order to select the aqueous molality of a particular component for plotting as abscissa.

PARTIAL_PRESSURE

takes the value SUBSTANCE(*)

This parameter can be used to select the partial pressure (pressure/standard state pressure) of an individual gaseous species for plotting as abscissa. The value SUBSTANCE should be subscripted (in brackets) by the number of the chosen substance and not its name eg "par=su(11)".

PRESSURE

takes the value SYSTEM

This parameter can be used to select the overall pressure of the system under consideration for plotting as abscissa eg "press=sys".

VOLUME

takes the value SYSTEM

This parameter can be used to select the overall volume of the system under consideration for plotting as abscissa eg "vol=sys". This normally means the volume of the gas phase.

TEMPERATURE

takes the value SYSTEM

Eh

takes the value H/+_ION_MOLALITY

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

abscissa 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

takes the value H/+_ION_MOLALITY

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

abscissa 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>)

LOG_SCALE

takes the values YES/NO

This parameter allows the user to choose between a logarithmic or linear abscissa scale. "log=y" gives a logarithmic scale and "log=n" gives a linear scale. The default is a linear scale.

RECIPROCAL

takes the values YES/NO

Enables the user to plot the reciprocal of the chosen abscissa 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 abscissa will cancel any previously selected LOG_SCALE.

+

takes the values <number> or NONE

This parameter is used to offset all ABSCISSA 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:

abscissa temperature system + ­273.15 !

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

abscissa 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 ABSCISSA 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 abscissa 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 abscissa 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.

DEFAULT

takes no values

This parameter can be used to select the variable originally STEPped in MULTIPHASE for plotting as abscissa. It takes no values. Before choosing a different abscissa variable it is wise to plot at least one graph with the default to check that the new choice being planned is prudent.

USER_VARIABLE

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

abscissa user_variable viscosity !

abs us_v batch_number !

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 14 April 2010