Flouride salt safety issues? (high temperature)

[Jack_O]

Hello, I am working a on a project to improve the thermal properties (heat capacity, thermal conductivity) of heat transfer fluids used in concentrated solar power (CSP). First a suitable base fluid is required, the higher the working temperature the better for thermal efficiency. Most of the work so far is based on carbonate and nitrate salts but most of these break down over 600dC. I recently read a paper titled 'High Temperature Liquid Fluoride Salt Closed Brayton Cycle Solar Power Towers' which attempted to suggest work done on nuclear power plants could be applied to CSP.

I would be interested in experimenting with these salts (such as NaF–KF–ZrF4, LiF–NaF–KF etc eutectic mixes) in the lab but some of my colleagues have expressed concerns that fluoride based salts could release fluorine gas. The paper mentions 'Liquid fluoride salts have been injected into water with no violent reactions (steam explosion or chemical reaction)' but does not mention the potential for gas release. High temperature testing would be with small amounts in DSC and TGA. My background is more physics than chemistry so any advice is welcome.

 

[Jack_O]

TL;DR can salts such as NaF form F₂ gas under high temperatures?

 

[DrDu]

TL;DR can salts such as NaF form F₂ gas under high temperatures?

I doubt it. More plausible would be generation of some hydrogen fluoride in reaction with water.
There must be some literature on it. There are many optical glasses based on fluorides and they are obviously also generated from the melt.

 

[MrSid]

Hello, I am working a on a project to improve the thermal properties (heat capacity, thermal conductivity) of heat transfer fluids used in concentrated solar power (CSP). First a suitable base fluid is required, the higher the working temperature the better for thermal efficiency. Most of the work so far is based on carbonate and nitrate salts but most of these break down over 600dC. I recently read a paper titled 'High Temperature Liquid Fluoride Salt Closed Brayton Cycle Solar Power Towers' which attempted to suggest work done on nuclear power plants could be applied to CSP.

One difference is that nuclear plant engineers can afford to use exotic corrosion resistant alloys for containment. You platens in your DSC TGA may not be up to it for the testing with Fluoride melts.

If I understand your premise, it is that you are looking for safety features that would be possible from the use of these fluoride melts at high temperatures if accidental release into the secondary water boiler was to happen. There would obviously be the tradeoffs of the materials of construction, vs corrosion effects for any working fluid at those temps. Good luck!