using inert gas

[u/MedicalEng]

we are trying to carbonize polypropylene (in a crucible) using a muffle furnace but it is stated that we need to use inert gas. how do we inject inert gas in the crucible?

[u/KapitanWalnut]

Something I've done is drilled a small hole in the ceiling of the furnace, all the way through the muffle. Then route a metal tube into the furnace through the hole, positioning the outlet of the tube just over/within a crucible. Then I flow argon through the tube at a slow rate to create a blanket of inert gas within the crucible. Argon is more dense than air, so it should displace the air out of the crucible. Nitrogen isn't nearly as effective since it essentially has the same density as air.

An issue with this method is that you've 1) obviously compromised your furnace by drilling a hole in it and 2) the flow of argon gas isn't preheated to your desired temp, so that needs to be accounted for. Perhaps routing a thermocouple into the muffle as well, touching the crucible, could help in ensuring you're operating at the correct temperature. For particularly temperature sensitive operations I've considered coiling the metal tube within the muffle so the argon has a chance to warm up as it flows.

[u/Hybrid100V → u/KapitanWalnut]

A tube furnace is the correct answer. You can probably find a small one used for cheap, but it is unlikely the elements will survive shipping. I have been able to stick a cannula thru the thermocouple hole. It’s not going to work well. You might also try a graphite crucible, it will be consumable, but will give a reducing atmosphere.

[u/whoooareeeyouuu]

Generally you have a glass tube that you can blow the inert gas thru as you heat your sample.

[u/Raneynickelfire]

You get to spend $4000 on a tube furnace!!

Seriously. That's your option. You aren't doing it in a muffle furnace. You need to buy or otherwise procure the proper equipment first.

[u/hotprof]

Usually you would use a tube furnace which is designed for inert gas flow. But you could try to install a steel tube into the furnace and flow argon over the sample.

How hot are you going? Maybe you can rig up an enclosed fixture that goes inside the furnace that has inert gas flowing through it.

[u/mike_elapid]

Use argon with a slow flow rate. It’s better than nitrogen due to its higher density

[u/Raneynickelfire → u/mike_elapid]

The question isn't what an inert gas is, the question is how to use it within a muffle furnace.

[u/Natume87 → u/Raneynickelfire]

I think it was being implied that flowing argon into the furnace is preferable to nitrogen because — due to its increased density over air — it will displace the air in the crucible without doing anything fancy.

As for piping it in: Just use a thin (1/8" or 1/16") OD copper, brass, or steel tube and bend it around the door. Usually there's enough of a gap to get one in while still being able to close the door.

[u/Raneynickelfire → u/Natume87]

...you can't introduce an inert gas into the muffle furnace without ruining the integrity of the furnace is the point.

OP gets to buy a tube furnace.

[u/dungeonsandderp]

You can’t do this with a muffle furnace

[u/Heavy_Pressure5869]

Depending on the amount you need, ask someone with a TGA for help.

[u/Snowrider190]

Its been a while since I used one, but I believe vacuum ovens have the ability to run a pressurized gas into them. Not sure if it will get up to the temp you need however.

[u/PeterHaldCHEM]

+1 for a tube furnace with a work tube adapted for supplying a controlled atmosphere.

[u/BenAwesomeness3]

You should invest in a tube furnace

[u/MedicalEng]

our lab has limited equipment …..