Appendix E: Thermochemical Data-files - Structure and Handling

Thermochemical data-files for use with ChemApp, FactSage, ChemSage, and ChemSheet come in a number of formats (see Chapter 1.11). Of these formats, only thermochemical data-files in ASCII format can be read and edited by the user. The basic structure of such a ChemSage data-file in ASCII format is shown in Table 24. It comprises four sections:

  1. a header section
  2. data block(s) for mixture phases
  3. data block(s) for stoichiometric condensed phases
  4. a commentary block containing a text description of the data-file.

The appearance of the header section consists of six lines and is similar for all data-files. The content of the data blocks for mixture and stoichiometric condensed phases depends on the system under consideration. A commentary block can be added to the data-file after the last line of data. This can include, for example, comments, references to data sources, a quality code, limitations on the use of the data-file, etc.

Stoichiometry matrix

The stoichiometry matrix defines the relationship between the species of a system and the system components. It provides information important for the determination of the mass balances in a Gibbs energy minimisation calculation. Hence, it is of great significance in the successful compilation of a thermochemical data-file. Refer to Chapter E.3 for details on the structure of the stoichiometric matrix and guidance on its preparation.

The reference [Eri90] provides additional information.

Table 24: The basic structure of a ChemSage data-file

HEADER
Six lines with a descriptive title and five lines of code containing general information
DATA BLOCK(S) FOR MIXTURE PHASES
Each block contains: phase name, model name; and the following information for all phase components - name, thermochemical data option, number of consecutive temperature ranges, stoichiometry coefficients, Gibbs energy data, and, if applicable, excess Gibbs energy data for
Mixture Phase 1
Mixture Phase 2
.
.
.
Mixture Phase 'n'

DATA BLOCK(S) FOR STOICHIOMETRIC CONDENSED PHASES
Stoichiometric Condensed Phase 1
Stoichiometric Condensed Phase 2
.
.
.
Stoichiometric Condensed Phase 'n'

COMMENTARY BLOCK
A text providing information on the origin of the data file, a quality designation, as well as a definition of the scope and areas of application of the data-file.



E.1: The format of a ChemSage data-file

The format of a ChemSage data-file is described in detail below, based on the sample data-file cosi.dat.

START OF HEADER SECTION

Line 1Descriptive title
The title may be up to 78 characters long, and can be used to provide a brief description of, for example, the contents of the data-file and the source of the data. The title below describes the data-file cosi.dat supplied with ChemSage and ChemApp.

C-O-Si, also used for silicon arc furnace reactor calculations

Line 2Code defining the size of the data-file
First digit: number of system components
Second digit: number of mixture phases
Third to last but one digit: number of phase constituents in the mixture phases
Last digit: number of stoichiometric condensed phases.

Note: The gas phase must always be considered as mixture phase number 1.
Note: If a gas phase is not present in the data-file, the number of its components must still be included and set to 0.

3   1  15   7

Line 3List of components in the system
The names of the components are listed, as shown. Each string must consist of 24 characters, including empty spaces.

Note: If more than three components are contained in the system, extra lines must be used.

C                          O                          Si

Line 4Molecular weights of the system components. Use extra lines if appropriate.

    12.0110      15.9994      28.0860

Line 5Definition of the temperature dependence terms for phase components and stoichiometric condensed phases in the Gibbs energy equation, G(T) = A + B*T + C*TlnT + D*T 2 + E*T 3 + F/T + (G*T U + H*T V + I*T W + J*T X + K*T Y + L*T Z)

The equations can contain up to 12 terms. The first six terms are standard; once they are defined, they are valid for all substances contained in the data-file.

The last six terms (maximum) can be defined individually for each substance using real numbers, and thus derive separate Gibbs energy equations for each substance. The powers U to Z can have real number values between -9 and +9. Note: You can enter 99 for ln(T).

The entry in the data-file consists of the total number of standard terms defined, and their positions in the Gibbs energy equation. The code below for the cosi.dat data-file indicates that all of the first six terms are defined, and that the following equation applies, G(T) = A + B*T + C*T*lnT + D*T 2 + E*T 3 + F/T

  6   1   2   3   4   5   6

Line 6Definition of the temperature and (if applicable) pressure dependence terms for the concentration coefficients in the excess Gibbs energy equation, L(T,P) = A + B*T + C*T*lnT + D*T 2 + E*T 3 + F/T + G*P

Any number of the seven terms in the equation may be used. An entry consists of the total number of terms defined and their position in the Gibbs energy equation. For example, the entry below in the cosi.dat file defines the equation, L(T) = A

  1   1

This ends the data entry for the header section of a data-file. The content of the six-line header for the data-file cosi.dat is summarised below.

HEADER SECTION OF THE DATA-FILE COSI.DAT


C-O-Si, also used for silicon arc furnace reactor calculations
  3   1  15   7
C                        O                          Si
     12.0110      15.9994      28.0860
  6   1   2   3   4   5   6
  1   1

END OF THE HEADER SECTION

START OF DATA BLOCK FOR MIXTURE PHASE(S)

Data are entered for all n mixture phases included in the system in any order sequence, except for the gas phase - this must always be considered as the first mixture phase. If a gas phase is not present, the number of its constituents must be set to 0. Data for each constituent of a mixture phase are entered successively, as shown below.

Data block for mixture phase 1 - the gas phase

Entry 1The phase name
GAS

Entry 2The model name - IDMX (ideal mixing)
IDMX

Note: Data for excess model coefficients are usually entered after the data entry for the last phase constituent. These contributions are not present in the case of ideal mixing (IDMX).

Data for component 1 of mixture phase 1 - carbon

Entry 3The constituent name
C

Entry 4Thermodynamic data option for constituent 1

In the following entry, First digit: 1 = Gibbs energy equations, Second digit: number of Gibbs energy equations, Remaining digits: coefficients of the stoichiometry matrix. These are entered in the order defined in line 3 of the header.

  1   2   1.0   .0   .0

Entry 5The upper temperature limit (K) and the temperature coefficients for each of the six terms in the Gibbs energy equation, G(T) = A + B*T + C*T*lnT +D*T 2 + E*T 3 + F/T

 2000.0000       710457.00      -18.971944     -20.769400     -.27196000E-04
 .00000000E+00  .00000000E+00
 6000.0000       711696.00      -28.661644     -19.489100     -.35773200E-03
 .00000000E+00  .00000000E+00

End of the data entry for component 1 of mixture phase 1

Subsequently, data are entered for the remaining phase constituents using the same procedure. The complete entry for the gas phase as the first mixture phase in the data-file cosi.dat is summarised in shortened form below.

DATA BLOCK FOR MIXTURE PHASE(S) IN COSI.DAT


GAS
IDMX
C
 1 2   1.0    .0    .0
  2000.0000      710457.00     -18.971944     -20.769400     -.27196000E-04
  .00000000E+00  .00000000E+00
  6000.0000      711696.00     -28.661644     -19.489100     -.35773200E-03
  .00000000E+00  .00000000E+00
C2
 1 1   2.0    .0    .0
  6000.0000      826673.00      1.8085362     -30.685500     -.23765100E-02
  .71128000E-07 -508774.00
C3
 1 1   3.0    .0    .0
  4000.0000      774485.00      130.77556     -49.887100     -.35584900E-02
  .17642500E-06  602078.00
CO
  1 1   1.0   1.0    .0
  3000.0000     -119348.00     -5.9053738     -28.409400     -.20501600E-02
  .00000000E+00  23012.000
CO2
  1 1   1.0   2.0    .0
  3000.0000     -409930.00      89.365756     -44.141200     -.45187200E-02
  .00000000E+00  426768.00
O
  1 2    .0   1.0    .0
  2000.0000      243275.00     -21.813244     -20.874000      .25104000E-04
  .00000000E+00 -48743.600
  3000.0000      243168.00     -21.880544     -20.853100      .00000000E+00
  .00000000E+00  .00000000E+00
 :
 :
 :
Si
  1 1    .0    .0   1.0
  3000.0000      445338.00     -36.090244     -19.815400     -.50208000E-03
  .00000000E+00 -100416.00
 :
 :
SiO
  1 2    .0   1.0   1.0
  2273.0000     -110346.00     -8.3075638     -29.823600     -.41191500E-02
  .38004700E-06  103136.00
  6000.0000     -130585.00      101.41956     -44.358800      .14267400E-02
 -.62760000E-07  6301100.0
SiO2
  1 1    .0   2.0   1.0
  6000.0000     -325105.00      154.83356     -56.157600     -.15187900E-02
  .58576000E-07  604170.00

END OF DATA BLOCK FOR MIXTURE PHASE(S)

DATA BLOCK FOR STOICHIOMETRIC CONDENSED PHASES

The basic data format for each stoichiometric condensed phase is the same as that for the components of a mixture phase. The entry for carbon as a stoichiometric condensed phase is shown below. The entry for pure silicon in this example is different. The data are entered in the alternative form, based on the use of a four-term heat capacity equation and explicit values for Delta H298 and S298.

Note: If different structural varieties of the same stoichiometric composition are to be treated explicitly, they must be given as separate phases.

Data entry for a stoichiometric condensed phase - carbon


C
1 3    1.0    .0    .0
 800.0000      -1153.5000     -12.583000       3.0258000     -.23742000E-01
 .39214000E-05  22809.000
1900.0000      -12380.000      139.22000      -20.022000     -.24390000E-02
 .19766000E-06  1066600.0
 6000.0000     -17431.000      178.95000      -25.499000     -.98209000E-04
-.15854000E-07  1897800.0

Data entry for a stoichiometric condensed phase - pure silicon

The data for pure silicon are entered using a four-term heat capacity equation and explicit data for the enthalpy of formation (Delta H298), the entropy (S298), and temperatures and enthalpies of transformation. The heat capacity equation has the form Cp = a + b*T + c*T 2 + d/T 2

Note: Heat capacity data may be entered only if the Gibbs energy equations are defined as in line 5 of the header section, i.e. 6 1 2 3 4 5 6.

Note: For pure silicon, both the solid and liquid state are included in the same set of Gibbs energy data.

Note: Transformation enthalpies are entered for all transition temperature inputs, except the last.

Entry 1Phase name
Si

Entry 2Thermodynamic data option (7 = enthalpy, entropy, and four-term heat capacity equations), number of data inputs (i.e. temperature ranges for which specific heat data are available), coefficients of the stoichiometry matrix.
 7 2 .0 .0 1.0

Entry 3Enthalpy in J.mol-1 at 298.15 K, and entropy in J.K-1mol-1 at 298.15 K.

 .00000000E+00  18.819600

Entry 4Upper temperature limit in Kelvin, the four coefficients of the heat capacity equation (a, b, c, and d) applicable at temperatures up to the maximum temperature, Tmax(1).

Tmax(1)          a             b                c                 d
1685.0000   22.823720    .38576480E-02    .00000000E+00     -353966.40

Entry 5Delta H(trans1) at Tmax(1)

50208.000

Entry 6Same input as for Entry 4, for Tmax(1)<T<Tmax(2)

Tmax(2)          a             b                c                 d
3492.0000   27.196000    .00000000E+00    .00000000E+00    .00000000E+00

No transformation enthalpy is entered here, since this is the last data range.

Data entry for a stoichiometric condensed phase - SiC


SiC
1 1   1.0    .0   1.0
 3259.0000     -91845.000      280.43000     -42.593100     -.41798200E-02
 .21198900E-06  829687.00

Data entry for a stoichiometric condensed phase - SiO2(quartz)

In this case, three extra terms in the Gibbs energy equation are applied, as discussed in the remarks to line 5 above.

Entry 1Phase name
SiO2(quartz)

Entry 2Thermodynamic data option (4 = Gibbs energy coefficients of the standard equation for terms 1 to 6, and additional terms used), number of Gibbs energy equations, and coefficients of the stoichiometry matrix.
  4 3 .0 2.0 1.0

Entry 3Upper temperature limit in Kelvin and temperature coefficients of the first Gibbs energy equation in Joule (see line 5)

 373.00000  -935388.53      536.02533     -80.011990      .00000000E+00
 .00000000E+00  1773342.0

Entry 4Additional terms used
First digit: 3 = number of additional coefficients
Remaining numbers: 3 coefficient/power pairs

3 .00000000E+00   4.0   -961.10400   .5   -81928064.    -2.0

Entry 5Upper temperature limit in Kelvin and temperature coefficients of the second Gibbs energy equation in Joule (see line 5)


 848.00000  -935486.57      537.07568     -80.011990     -.42200108E-02
 .75354500E-05  1773342.0

Entry 6Additional terms used

First digit: 3 = number of additional coefficients
Remaining numbers: 3 coefficient/power pairs


3  .50458704E-08   4.0  -961.10400      .5  -81928064.     -2.0

Entry 7Upper temperature limit in Kelvin and temperature coefficients (see line 5) of the third Gibbs energy equation in Joule

 1744.2500  -933315.35      533.27853     -80.011990      .00000000E+00
 .00000000E+00  1773342.0

Entry 8Additional terms used

First digit: 3 = number of additional coefficients
Remaining numbers: 3 coefficient/power pairs


3  .00000000E+00   4.0  -961.10400      .5  -81928064.     -2.0

End of data entry for SiO2(quartz)

Note: For the above entries, the extra terms do not have to use the same powers in each range. It is a coincidental in this example. All other phases of SiO 2 are treated in the same way as SiO 2(quartz). The data block is summarised below.

DATA BLOCK FOR STOICHIOMETRIC CONDENSED PHASES IN COSI.DAT


C
  1 3   1.0    .0    .0
  800.00000     -1153.5000     -12.583000      3.0258000     -.23742000E-01
  .39214000E-05  22809.000
  1900.0000     -12380.000      139.22000     -20.022000     -.24390000E-02
  .19766000E-06  1066600.0
  6000.0000     -17431.000      178.95000     -25.499000      .98209000E-04
 -.15854000E-07  1897800.0
Si
  7 2    .0    .0   1.0
  .00000000E+00  18.819600
  1685.0000      22.823720      .38576480E-02  .00000000E+00 -353966.40
  50208.000
  3492.0000      27.196000      .00000000E+00  .00000000E+00  .00000000E+00
SiC
  1 1   1.0    .0   1.0
  3259.0000     -91845.000      280.43000     -42.593100     -.41798200E-02
  .21198900E-06  829687.00
SiO2(quartz)
  4 3    .0   2.0   1.0
  373.00000     -935388.53      536.02533     -80.011990      .00000000E+00
  .00000000E+00  1773342.0
 3  .00000000E+00  4.0 -961.10400       .5 -81928064.     -2.0
  848.00000     -935486.57      537.07568     -80.011990     -.42200108E-02
  .75354500E-05  1773342.0
 3 -.50458704E-08  4.0 -961.10400       .5 -81928064.     -2.0
  1744.2500     -933315.35      533.27853     -80.011990      .00000000E+00
  .00000000E+00  1773342.0
 3  .00000000E+00  4.0 -961.10400       .5 -81928064.     -2.0
SiO2(tridymite)
  4 2    .0   2.0   1.0
  390.15000     -946102.84      500.41936     -75.372670     -.91038535E-01
  .20563620E-03  2979047.5
 3 -.17418275E-06  4.0  .00000000E+00   .5 -.15970769E+09 -2.0
  1991.2800     -944111.17      480.75284     -75.372670      .00000000E+00
  .00000000E+00  2979047.5
 3  .00000000E+00  4.0  .00000000E+00   .5 -.15970769E+09 -2.0
SiO2(cristobalite)
  4 3    .0   2.0   1.0
  535.15000     -926547.67      571.80290     -83.513600     -.10104998E-01
  .20917698E-04  1227680.0
 3 -.16237635E-07  4.0 -1498.7720       .5 -46678699.     -2.0
  1995.9900     -924997.14      566.99971     -83.513600      .00000000E+00
  .00000000E+00  1227680.0
 3  .00000000E+00  4.0 -1498.7720       .5 -46678699.     -2.0
  3000.0000     -961789.83      569.34943     -85.772000      .00000000E+00
  .00000000E+00  .00000000E+00
 3  .00000000E+00  4.0  .00000000E+00   .5  .00000000E+00 -2.0
SiO2(liquid)
  4 2    .0   2.0   1.0
  1995.9900     -915415.78      562.19940     -83.513600      .00000000E+00
  .00000000E+00  1227680.0
 3  .00000000E+00  4.0 -1498.7720       .5 -46678699.     -2.0
  3000.0000     -952208.47      564.54913     -85.772000      .00000000E+00
  .00000000E+00  .00000000E+00
 3  .00000000E+00  4.0  .00000000E+00   .5  .00000000E+00 -2.0

END OF DATA BLOCK FOR STOICHIOMETRIC CONDENSED PHASES

Data-file commentary

 Date           : Nov.1992
 Originator     : KH+GE
 Serial No      : COSI.DAT
 Quality Status : A
 ChemSage Vers. : 4.0
 
 Temperatures   : RT to 3500K
 Compositions   : All
 Applications   : Phase equilibria and thermodynamic properties.
 
                  This files serves as an example of input for several type
                  of Gibbs energy data of pure substances, e.g. simple
                  G-functions with several temperature ranges (Type 1), H-S-Cp
                  input with implicit phase transformation (Type 7), extended
                  G-functions with several temperature ranges (Type 4).
 
                  Note that this file is also used in conjunction with the
                  reactor definition file REACTOR.DAT for the simulation of
                  a silicon arc furnace.
 
                  See Handbook, pages 262 and 227 (REACTOR.DAT)
 Sources of data
 
 Unary          : THERDAS (90Spe); silicates from 85Ber
 Binary         : None
 
 References     : 85Ber Berman,R.G.; Brown,T.H.; Greenwood,H.J.: Atomic
                        Energy of Canada Limited, TR-377, 1985
                  90Spe Spencer,P.J.; Hack,K. : Swiss Materials 2,3a,
                         1990, p69

If you prepare your own data-files, we recommend that these be documented in a similar manner to that described above for GTT data-files; preferably using the 'K' option of the DATA INPUT module of ChemSage, providing, for example, source(s) of the data, literature references, and other relevant information.



E.2: Data-files with preset suppression of species

In some cases it might be chosen to suppress phases or phase constituents from calculations (i.e. set their status to 'DORMANT', see Table 11).

When a miscibility gap exists in the system

In such cases, the phase which exhibits the miscibility gap is contained twice in the data-file, but used only once in a normal phase equilibrium calculation. Hence, the second entry of this phase is suppressed from normal calculations by marking it with an exclamation mark ('!') in the 26th column of the data-file, see above.

Note: When calculations are performed in composition and temperature regions close to the miscibility gap, the second phase must be re-entered during run time by calling the subroutine TQCSP.

When a data-file does not cover the entire composition range of a system

This is almost always the case when one of the phases has been described with a dilute solution approximation. In such cases, the file may contain phases, which are not stable under many conditions. These phases are suppressed in the data-file in order to speed up the calculations. However, it is important to monitor the results for the activities of these phases in the equilibrium output table, and to re-enter the phase and repeat the calculations if activity values greater than one are found.

GTT-Technologies may sometimes supply standard or customised data-files with suppressed species; which species have been suppressed and the reason why will be described in the commentary section.

If phases or phase constituents are to be assigned the status 'ELIMINATED' (see Table 11), this can also be preset in the data-file. In this case a double cross ('#') is placed in the 26th column of the line containing the name of the phase or phase constituent in question. In both cases, the status can always be changed during run time using TQCSP and TQCSPC.



E.3: Definition of a stoichiometry matrix

The stoichiometry matrix defines the compositional relationship between the species of a system and the system components. The number of mols of each element in any species is presented in a fixed, repeatable form. A dataset for the specific species is formed by adding thermodynamic data (Gibbs energy coefficients) to the stoichiometry matrix.

In a stoichiometry matrix, each species is defined by a line, and each component by a column. For example, consider a system with the independent components Cr and C, in which the solid compound Cr23C6 exists. The stoichiometry matrix for 1 mol of Cr23C6 is

                         C     Cr
Cr23C6                   6     23

If a third element is present, e.g. Fe, an additional column is added, and the stoichiometric matrix for 1 mol of Cr23C6 becomes

                         C     Cr    Fe
Cr23C6                   6     23     0

Sometimes it is more convenient to refer to 1 mol of atoms in the phase, the matrix then has the following form:


                         C     Cr    Fe
(Cr23C6)/29           0.2069 0.7931   0

Stoichiometry Matrix Plus Data Equals Dataset

The following example demonstrates the entry of the stoichiometry matrix with Gibbs energy coefficients to form a dataset for Cr23C6 for a system containing only C and Cr.


Cr23C6
1 1   6.0   23.0
 1823.0000   -655776.00     4251.6000    -707.76500     -.89244700E-01
0.00000000      6052160.0

If more than two components are contained in a system, zeros are added to the stoichiometric matrix to represent the presence of the other components. This is shown in the next example, in which C is the second and Cr the fourth system component in a system containing a total of eleven components:


(Cr23C6)/29
1 1   0.0 .2069   0.0 .7931   0.0   0.0   0.0   0.0   0.0   0.0   0.0 
 1823.0000    -22613.000     146.60700    -24.405700    -.30774000E-02
0.00000000      208695.00

The example above also demonstrates the use of the matrix in reference to 1 mol of atoms. Note that any scaling of the stoichiometric coefficients of a species, caused by this type of entry, must also be accompanied by an identical scaling of the Gibbs energy coefficients. In addition, in order to avoid possible confusion when reading the output tables, it is good practice to change the species name, as in this case to (Cr23C6)/29.


ChemApp Programmer's Manual, Edition 3.6© GTT-Technologies, 2003