Fluorine outgassing from PTFE

[semmaker]

I am using PTFE coated wires in a vacuum system. It is being baked to 200 C to facilitate getting the proper vacuum level. I have an SRS residual gas analyzer for monitoring the system. After the 20 hour bake I see the RGA head is contaminated with F. Does anybody know the temperature at which F is liberated from PTFE?

 

[Demon3]

It is my understanding that there should be zero fluorine coming out of your PTFE. PTFE is table to much higher temperatures than those you mention. Many gas detectors give false readings, i.e. they are not only detecting the intended gas. You might check to see if the detector also "sees" other gases (in the manual). If PTFE gave off fluorine gas at cooking temperatures then there is no way it would be allowed for non-stick frying pans and ovenware. I have looked a little at the stability of PTFE for non-stick coatings and saw no decomposition until near 300 Celcius.

 

[semmaker]

Thanks Demon3. To explain a little further I don't see the F peak prior to baking the system. This may be explained by the large water peak at 18 masking the smaller F peak at 19. After I bake I see F along with a lesser peak of HF. I believe F is being liberated from somewhere during the bake cycle and is then condensing on my RGA head and contaminating it. When I turn on the RGA filament F is released and of course detected. Since my system is mostly H2 after the bake a smaller peak at HF would tend to support the 19 peak is indeed F and not another gas. As I thought about it some more another possibility is contamination from the grease used to lubricate hardware clamping the conflat flanges. It is based on a perfluoropolyether oil. I'm sure that no matter how careful the assembly is done it is not possible to keep some small amount of this from getting into the system.

 

[Demon3]

Thanks for the explanation. Perhaps you can just bake a sample of the grease alone then and see if that gives the peaks. Or contact other suppliers of PTFE coatings and see whether they have systems that do not give off nasty stuff. PTFE is listed as OK for continual use to rather high temperatures so it really should not decompose at all at 200°C.