radiance88
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Thermocouples
I'm curious about these since I have an analog hotplate but still want to record temperatures.. Can't one just use a thermocouple that attaches onto a
multimeter to measure the temperatures of solutions?
However, most of the thermocouples that come with these don't look like the typical ones that you get from a hotplate- they are literally just two
pieces of wire attached at the tip. Wouldn't using this be a bad idea if somehow something in the solution started to react with the metal?
Should one only use one of those probes that come with hotplates? Since those are stainless - wouldn't those also react as well given the right
solution?
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Magpie
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I buy my thermocouples, thermocouple wire, etc here:
http://www.omega.com/section/thermocouples.html
The UK likely has an equivalent source.
The ones I buy are 1/8" diameter, 12" long, K type IIRC. The outer case is some kind of ss. They run ~$25.
If you want I can look up the specs for you.
The single most important condition for a successful synthesis is good mixing - Nicodem
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Zombie
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You can buy them all over Ebay as well. I have 2 12 voly Digital temp meters I bought with K type couples for 19.99 / Free shipping (from China) This
link is just one example.
http://www.ebay.com/itm/2-52mm-EGT-Exhaust-Gas-Temp-Gauge-Me...
The set I bought allowed me to order a specific probe length, and like Magpie, I ordered a 12" couple.
Look up Exhaust Gas Temp. Gauge. The range is up to 760* C
They tried to have me "put to sleep" so I came back to return the favor.
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Fulmen
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You are right, chemical compatibility is a major issue when choosing temperature probes. Bare wires are best suited for air and inert gases, stainless
steel are good for general purpose. But for corrosive chemicals other materials must be chosen, not sure how easy they are to get hold of. I wonder if
it's possible to seal such wire in something like a capillary glass tube without destroying it, challenge will be to keep it from shorting out other
than at the tip. A piece of braided glass insulation could work. I guess.
We're not banging rocks together here. We know how to put a man back together.
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Magpie
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Here's the one (type K) I have ordered, twice. The 1st one just wore out due to hard use in my tube furnace, etc.
http://www.omega.com/pptst/KMQXL_NMQXL.html
The single most important condition for a successful synthesis is good mixing - Nicodem
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Dr.Bob
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They sell Teflon coated thermocouples as well, I have used them many times. You can also get them in stainless steel jackets for some applications.
I still have a variety of type K and T thermocouples left, as well as some connectors and extension cords for them. I will try to get some photos
of what is left of each type and post them. But I would not use the bare wire type for much exposed work, as they will not last long exposed to most
chemicals.
[Edited on 20-2-2015 by Dr.Bob]
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Praxichys
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I take short sections of 6mm glass tubing and close one end in a flame. A standard bare thermocouple can be pushed to the bottom. This is an effective
thermocouple probe for the most corrosive of environments.
Glass is not a very good conductor of heat, so response is a bit slow. Backfilling the tube with oil behind the probe could help.
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DJF90
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Quote: Originally posted by Praxichys  | I take short sections of 6mm glass tubing and close one end in a flame. A standard bare thermocouple can be pushed to the bottom. This is an effective
thermocouple probe for the most corrosive of environments.
Glass is not a very good conductor of heat, so response is a bit slow. Backfilling the tube with oil behind the probe could help.
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This is exactly what we did when I was working in PRD. The glass pocket could be bent,in the flame, if required, to keep the closed end away from the
anchor stirrer (or stir bar, on small scale). The pocket can be filled with a little silicone oil (just 1 cm deep or so, sufficient for immersing the
thermocouple junction). For GMP work silicone oil is not allowed, so the reaction solvent was used instead.
One thing I will say... monitoring the internal temperature of your reaction is one of the most useful things you can do. Its
surprising how much difference there can be compared to the heating/cooling bath.
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Dr.Bob
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Could you use a 5 mm dia NMR tube as the glass tube? I had not thought of that before now, but they are easy to find, both 7" & 8", and would
fit into a 5mm thermometer adapter as well. You would not even need to seal the outside end then, although a dab of epoxy might be good to hold the
probe in place and keep the oil in it. That seems like a nice solution, and cheap.
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subsecret
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I don't see why an NMR tube wouldn't work... Just make sure it fits well into the adapter, because my 5mm tubes fit poorly, and required Teflon tape.
I use 7mm glass tubing with some oil in the tip.
@Dr. Bob: the epoxy is a great idea! I've had my thermocouple come out of the tube when handling, and it flung a little bit of oil around.
Fear is what you get when caution wasn't enough.
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radiance88
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I think that a glass-jacketed thermocouple probe would be the best fit, but it seems like I can't really find this on Ebay or elsewhere, strange
enough.
I found a teflon coated one - but I don't quite understand the connectors.
I may very well have to modify my own via Praxichys' method. . after I buy a bunsen and some glass tubing.
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Zombie
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The connectors are made for something like a PID or basic universal gauge.
It's no big deal at all. Take whatever connector you now have, and splice the wires as close to the ends of the new probe as you can.
If the temp reads minus or the wrong direction, just reverse them.
Just looked again... You don't have a connector.
It's still easy if your plate has the port for a thermocouple. You can buy a connector on line for a dollar or so, or splice onto your plate or meter
inputs.
Really no big deal at all.
They tried to have me "put to sleep" so I came back to return the favor.
Zom.
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