I have to heat my round bottom flask to >300 C for my reaction. At the same time, the reaction has to be protected under nitrogen atmosphere. Is there a thermocouple joint adapter that can hold a 3 mm diameter thermocouple while retaining an airtight seal between the temperature probe and standard taper joint (size: 19/22)? I have seen thermocouple joint adapters made of PTFE and others made of glass coupled with a nylon bushing, but I am concerned that the PTFE and nylon will not remain chemically stable at this high of a temperature.
Many thanks for your help.
The solutions given above are good ones. We found that using such a tube dramatically slowed the thermocouple response. Not surprising... but even using a heat transfer fluid (rather than glass wool) we found it was too slow for our preference.
For the commercial products with plastic parts, I guess the question is how much higher than 300 C? If you are working below 350 C, I'd guess Teflon would probably be okay, since I doubt the part of the joint that is teflon is anywhere near that temperature- I'd even guess it is below 200 C. Typically, the necks of the flask are much cooler than the bottom working volume, unless you have some fairly unusual geometries. You could easily test this approximately by placing a thermocouple against the top part of the neck at the lowest height where there would be Teflon.
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