Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Molten Salt

  1. May 2, 2007 #1
    Generally, when you melt a salt (CaCl2 @800deg C specifically) are the ions disassociated as in a solution or is molecular vibration simply great enough to not allow the formation of intermolecular bonds and the atoms are floating around still paired? This is probably a dumb question and my overwhelming instinct is the latter, anyone care to confirm?

    Also, will there be the potential for Chlorine gas to be produced to be exhumed from the molten salt, again my instinct is no, but at such high temperatures there might be the potential for the ionic bonds to be displaced in a collision and form Cl2? Enthalpy of formation of CaCl2 is -795.4 kJ/mol for a solid, I'll see if I can find it for a liquid and run the numbers for the reaction CaCl2(l) -> Ca(?) + Cl2(g). Would this reaction be accelerated if there was a galvanic cell taking place in the mix?
    Last edited: May 2, 2007
  2. jcsd
  3. May 2, 2007 #2


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    Most molten salt solutions conduct electricity so they exist as ions. As for producing chlorine, it is possible if the temperature is high enough.

    CaCl2 + heat <--------> Ca + Cl2(g)

    As shown the reaction is reversible. Just add heat to force the reaction to the right. How much heat (temperature) is the question. I do not know the decomposition temperature of CaCl2 but it can be found easily, I'm sure.
  4. May 5, 2007 #3
    This is simply molten anhydrous molten salt, so I don't think that qualifies it as a solution. It is a solvent to some solutes like CaO but that is on a minimal scale so maybe like water it is those impurities which make it an electrolyte, but as the process that I'm designing is supposed to purify the salt. Would it still be an electrolyte?

    I know in the Plutonium electro-refining process they use a separate PuF4 electrolyte in the molten salt medium.

    So I ask again what is the molecular nature of molten salt? Is there a dissociative rate of the ions or do they exist as free flowing CaCl2 molecules?


    Molten salts conduct electricity the same way they do when they are dissolved in water; some of the salt molecules are dissociated into ions, which allows the ions to conduct electricity. The "Downs Cell" capitalizes on this conduction of electricity to produce virtually all of the metallic sodium required by industry. Electricity is run through molten sodium chloride (with a little calcium chloride salt added to lower the melting point of the sodium chloride). At one terminal chlorine gas is released (the anode) and at the other (the cathode) liquid sodium.

    Found this google cache with some good information and references. Now I need to try and qualify the percentage of ions floating around in the mix, any ideas?
    Last edited: May 5, 2007
  5. May 7, 2007 #4


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    If it is your intention to purify this salt by melting and applying some process to the molten salt, the molten salt does behave as a solution. It is a solution for the impurities...

    At 800 C, CaCl2 probably doesn't dissociate into Cl2. The term you are looking for is "activity of molten salt solutions".

    See here:

Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?

Similar Discussions: Molten Salt