JANAF

This module gets thermodynamic data from the JANAF database. Files are downloaded from the NIST servers as needed and then cached locally.

Zack Gainsforth

Funding by NASA

class thermochem.janaf.JanafPhase(rawdata_text)

Class which is created by Janafdb for a specific phase.

It reads in the JANAF data file and produces functions which interpolate the thermodynamic constants.

Tr stands for reference temperature and is 298.15 K

>>> db = Janafdb()
>>> p = db.getphasedata(formula='O2Ti', name='Rutile', phase='cr')
>>> p.cp([500, 550, 1800]).astype(int).tolist()
[67, 68, 78]
>>> print(p.S([500, 550, 1800]))        # Entropy in J/mol/K
[  82.201    88.4565  176.876 ]
>>> print(p.gef([500, 550, 1800]))      # [G-H(Tr)]/T in J/mol/K
[  57.077   59.704  115.753]
>>> print(p.hef([500, 550, 1800]))      # H-H(Tr) in kJ/mol
[  12.562    15.9955  110.022 ]
>>> print(p.DeltaH([500, 550, 1800]))   # Standard enthalpy of formation in kJ/mol
[-943.670  -943.2295 -936.679 ]
>>> print(p.DeltaG([500, 550, 1800]))   # Gibbs free enegy in kJ/mol
[-852.157  -843.0465 -621.013 ]
>>> p.logKf([500, 550, 1800]).astype(int).tolist() # Equilibrium constant of formation.
[89, 80, 18]
>>> print(p.cp(1000))                   # Heat capacity in J/mol/K
74.852
>>> print(p.cp(50000))                  # Example of erroneous extrapolation.
Traceback (most recent call last):
    ...
ValueError: A value in x_new is above the interpolation range.

class thermochem.janaf.Janafdb

Class that reads the NIST JANAF tables for thermodynamic data.

Data is initially read from the web servers, and then cached.

Examples

>>> rutile = Janafdb().getphasedata(name='Rutile')

To load thermodynamic constants for TiO2, rutile.

getphasedata(formula=None, name=None, phase=None, filename=None, cache=True)

Returns an element instance given the name of the element. formula, name and phase match the respective fields in the JANAF index.

Parameters:

• formula (str) – Select records that match the chemical formula
• name (str) – Select records that match the chemical/mineral name
• phase (str) – Select records that match the chemical phase. Must be one of the following valid phases: cr, l, cr,l, g, ref, cd, fl, am, vit, mon, pol, sln, aq, sat
• filename (str) – Select only records that match the filename on the website, which is very unique.
• cache (bool, default True) – Whether to cache the Janaf database. Setting this to false will download the Janaf database every time it is used.

Examples

>>> db = Janafdb()
>>> db.getphasedata(formula='O2Ti', phase='cr')
Traceback (most recent call last):
    ...
ValueError: There are 2 records matching this pattern:
    ...
Please select a unique record.
>>> db.getphasedata(formula='Oxyz')
Traceback (most recent call last):
    ...
ValueError: Did not find a phase with formula = Oxyz
            Please provide enough information to select a unique record.
            Also check that you didn't eliminate the record you want by choosing too many constraints where one or more constraint is incorrect.
>>> db.getphasedata(formula='Oxyz', phase='l')
Traceback (most recent call last):
    ...
ValueError: Did not find a phase with formula = Oxyz, phase = l
            Please provide enough information to select a unique record.
            Also check that you didn't eliminate the record you want by choosing too many constraints where one or more constraint is incorrect.
>>> FeO = db.getphasedata(formula='FeO', phase='cr,l')
>>> print(FeO)
<thermochem.janaf.JanafPhase object at 0x...>
  Iron Oxide (FeO)  Fe1O1(cr,l)
    Cp(298.15) = 49.915 J/mol/K
    S(298.15) = 60.752 J/mol/K
    [G-H(298.15)]/298.15 = 60.752 J/mol/K
    H-H(298.15) = 0.000 J/mol/K
    Delta_fH(298.15) = -272.044 kJ/mol
    Delta_fG(298.15) = -251.429 kJ/mol
    log(Kf((298.15)) = 44.049

search(searchstr)

List all the species containing a string. Helpful for interactive use of the database.

Parameters:searchstr (str) – The search string to look for Returns:Dataframe containing valid phases Return type:pandas.DataFrame

Examples

>>> db = Janafdb()
>>> s = db.search('Rb-')
>>> print(s)
     formula           name phase filename
1710     Rb-  Rubidium, Ion     g   Rb-007
>>> s = db.search('Ti')
>>> print(len(s))
88