blogfast25
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Dry distillation of NH4F...
I've tried to buy NH4F (ammonium fluoride) in the UK for quite a while now without any success. Even obtaining its less dangerous homologue NaF hasn't
been easy but finally I've got some arranged by mail.
NaF really is no good for my project so I need to convert it to NH4F by the known route of dry distilling a mixture of NaF + NH4Cl ---> NH4F
↑ + NaCl.
Brauer provides a scant description of the procedure, including the ratio NaF/NH4Cl and to recover the sublimed NH4F on platinum foil. Whoop-ee,
finally an opportunity to use one of my many Pt crucibles (NOT)!
I've searched the board but found no one having constructed an apparatus that works without loss of NH4F to the environment.
I was thinking of using clean polypropylene (PP) as a 'cold trap', instead of Pt. Brauer also calls for 'gentle heating' (or words to that effect),
the sublimation point of NH4F acc. Wiki is about 100 C, so that would fit.
A steel crucible fitted with a tight fitting PP lid (perhaps modestly cooled?), gently, gently heated, perhaps over oil bath to 110 - 120C. Or perhaps
an assembly entirely of PP (MP = 165 C), heated with oil...
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Panache
International Hazard
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Registered: 18-10-2007
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Mood: Instead of being my deliverance, she had a resemblance to a Kat named Frankenstein
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i would just say that ensure your oil doesn't plasticise the PP at the temperatures you want to run at. You're not proposing to have a sealed system
are you? If you are then pull a moderate vacuum(~10inHG) on the system before sealing it, this works well for sealed distillations that result in a
liquid condensing on the condenser, i assume it would work similar for sublimable solids, but i don't know. Trial and error will tell.
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blogfast25
International Hazard
Posts: 10562
Registered: 3-2-2008
Location: Neverland
Member Is Offline
Mood: No Mood
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PP is quite resistant to even paraffinic oil for extensive periods of time if the temperature isn't too high. Silicone oil is better of course.
I wasn't thinking of a really sealed system, that was badly phrased. More of a sealed system with a long copper or brass chimney (a kind of 'snorkel',
if you like): any NH4F not condensing in the cooler lid of the 'apparatus' would condense in the cool chimney. In theory!
I don't look forward to this experiment but it has to be done. Start small will be the motto for the day, I guess...
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