•   about 8 years ago

Multiphase tables in Thermochemical data (SRD 13)


I just want to confirm my understanding here. When we encounter a multi-phase table (e.g. for crystalline and liquid phases), am I correct in assuming that this data just merely replicates the data in the appropriate single-phase tables (e.g. the crystalline-phase table and the liquid-phase table) for the phase that is most stable at each temperature?

In other words, could I reconstruct the multi-phase table from the respective single phase tables -- or does the multi-phase table contain additional information that I am not appreciating?



  •   •   about 8 years ago

    No. The multi-phase table is not just the simple concatenation of the single phase tables. Some quantities are the same, but some are not. Look at first case in tables Al(cr,l) (aluminum). [G-H(Tr)]/T and H-H(Tr) at 2800,2900,3000 K are NOT identical to the values in the Al(cr) OR Al(l). The difference is the Al(cr,l) includes enthalpies of phase transition while the individual phase do not (cannot). Don Burgess NIST

  •   •   about 8 years ago

    Thanks for the clarification. So for tables labeled (cr, l), enthalpies at temperature past the phase boundary will incorporate an enthalpy of fusion?

    Why aren't there many liquid-gas multi-phase tables that include a similar enthalpy of phase transformation for the liquid to gas transition?

    Thanks so much for your answers!

  •   •   about 8 years ago

    Every other (cr,l) table that I found looked like incorporated heat of fusion. I would strongly suggest not trying to deconstruct (cr,l) from (cr) and (l) or visa versa. Use the tables as is. That is what is requested, in fact.

  •   •   about 8 years ago

    Sure thing, I'll take your suggestion. I just want to make sure I understand the data. Thanks for all your help!

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