I have a need for a sodium salt that melts below 265 degrees celsius, which will be exposed to liquid sodium metal. The anion is not important, only that it has a sodium cation. I have done a lot of research and the nearest thing that I have found is sodium hydrogen sulfate. However, this specific salt will not work for what I need, because of a side reaction, namely that between Na metal and NaHSO4. The only option left that I can think of is a eutectic, consisting of only sodium salts (so no potassium hydroxide or the like). Are there any sodium salt eutectics that have a melting point of less than 265 degrees celsius?

  • $\begingroup$ As an additional keyword to consider, ionic liquids (or, IL) is a field with rising interest e.g., in catalysis and electrochemistry. NIST's database #147 compiles some information (including melting points) though it is up to the user to evaluate if these components are compatible with the chemistry intended (since Na may engage in redox reactions, e.g. by electrochemical window, etc.): ilthermo.boulder.nist.gov $\endgroup$
    – Buttonwood
    Jan 3, 2022 at 6:19
  • $\begingroup$ WP does not say sodium bisulfate melts anywhere near 265C. Rather it decomposes at 315C to sodium disulfate (Na2S2O7) which remains solid. In any event a eutectic based on NaOH seems better anyway. $\endgroup$ Jan 6, 2022 at 20:42

1 Answer 1


Calculation from the FACT thermodynamics package suggests a mixture of about 80 mol% NaOH and 20 mol% NaI (sodium iodide) will melt below 250°C.

enter image description here Source

  • $\begingroup$ Hm, NaOH plus sodium metal? $\endgroup$
    – Karl
    Jan 3, 2022 at 11:57
  • $\begingroup$ @Karl The halide component should read Na and then a capital eye, not Na and then a small ell. Unfortunately this confusion in nomenclature is with us unless we change the symbol for iodine from I to J. Sprechen sie Deutsch (iodine -> Jod)? $\endgroup$ Jan 3, 2022 at 12:06
  • $\begingroup$ Ja, it's especially bad with lousy font sets where capital "i" and regular "L" are indistinguishable. But I meant this from the original question above ".. which will be exposed to liquid sodium metal." $\endgroup$
    – Karl
    Jan 3, 2022 at 12:53
  • $\begingroup$ As for keeping the metal out of the hydroxide, you do need to keep the temperature low. The old Castner process for getting Na(liq) from molten NaOH required a tight temperature range to keep the electrolyte liquid but limit sodium solubility. Adding the iodide salt to lower the melting point would have actually helped. $\endgroup$ Jan 3, 2022 at 13:16
  • $\begingroup$ Why are you answering this OP all the time? He's asking about the same thing really and I think he's violating homework policy - has a task and wants us to do his research. $\endgroup$
    – Mithoron
    Jan 3, 2022 at 13:40

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