Yes, I am still alive! I have been out of the lab for a loooong time so the inspiration hasn't been there. However, I am now finding myself in the lab again and it appears that I will get to stay there for a while. And today inspiration struck.Let's talk about oil baths. Good way to heat stuff up in a controlled way, BUT, what a bloody mess they are. The oil becomes disgusting after a while, the glassware gets nasty, ocassionally oil baths break and make the mess from hell....
So whenever possible I use an aluminium heating block. However, we have a limited number of these in a limited number of shapes and sizes. When a heating block isn't available my next choice is a sand bath. These are traditionally used when you have to heat something to a ridiculous temperature that oil can't handle. However, I use them for any reflux (see picture). The problem with these things is that heat transfer isn't particularly effective so it's only really good for reflux and not for heating something at a well defined temperature below the boiling point. Also it can be quite tricky for the sand bath to heat up in a well ventilated fume hood so it is generally a good idea to wrap a bit of aluminium foil around the bath to get the heating going. D!
So whenever possible I use an aluminium heating block. However, we have a limited number of these in a limited number of shapes and sizes. When a heating block isn't available my next choice is a sand bath. These are traditionally used when you have to heat something to a ridiculous temperature that oil can't handle. However, I use them for any reflux (see picture). The problem with these things is that heat transfer isn't particularly effective so it's only really good for reflux and not for heating something at a well defined temperature below the boiling point. Also it can be quite tricky for the sand bath to heat up in a well ventilated fume hood so it is generally a good idea to wrap a bit of aluminium foil around the bath to get the heating going. D!
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14 comments:
Has anyone tried metal beads? It seems like it should work, and have higher thermal conductivity than sand. Corrosion might be an issue.
Aluminium foil is also useful. Get a sheet; fold it in half a couple of times, on a flat surface crush the foil around your flask until the foil reaches about half way up. You're left with a block of crushed aluminium with a concave shape that fits the rb flask. Useful for 100 ml and lower flasks.
Metal baths are usually ok, it's a bit tricky to cool them down when they have over-heated. The only thing is: get your glassware out as long as the metal is molten... :-)
Never heard about the sand before, but seems to be a good idea. We will try this in due time.
Graphite is supposed to be good as it conducts heat more readily than sand - choose a coarse grade or you'll end up with a horrific mess though.
The aluminium "DrySyn" blocks are fantastic and my personal favourite though
Oil baths are OK up to 180 ºC or so. May I ask what kind of reactions require temperatures higher that this? Reactions that do NOT yield insoluble-in-everything asphalts upon cooling to rt, preferably :)
For very high T reactions, I usually use 20 mL disposable vials and heat them in the microwave. Regardless of the outcome, I then don't have to worry about cleaning afterwards.
"Oil baths are OK up to 180 ºC or so. May I ask what kind of reactions require temperatures higher that this?"
http://www.orgsyn.org/orgsyn/pdfs/CV2P0423.pdf
I wouldn't call the resulting mixture an "insoluble-in-everything asphalt". I must however admit, this prep was a mess for several other reasons, and I hope I'll find another way to get that product.
I used a metal bath, by the way.
You can check out labarmor.com , those work nicely if you can heat bath from botom (heat plate). Peter.
As an example, Wolff-Kishner reductions often require temperatures above 200 ºC.
Any danger with the glass shattering? Pyrex beaker with sand surrounding a distillation flask.
Glass breakage is a HUGE issue. We do this in an organic lab and too much sand and heat to fast and CRACK. I have even had a student fuse a beaker to a ceramic hot plate. That hot plate still has glass embedded in the top after I had to break the beaker and chip of the glass/ceramic top!
An alternative to sand and oil is a universal hot plate attachment that sits on top of your hotplate. No more oil or sand in my lab!
LabFriend have universal options:
https://www.labfriend.com.au/c/9572/0/universal-reaction-block-system-for-magnetic-stirrer-s
Just pour sand into a heating mantle. Use a thermocouple to control the temperature through the sand or through whatever is in the container you are heating. You might need a set of heating mantles larger than you already have to accommodate the sand and the vessel but that should not be a big deal. You will, of course, need a thermocouple attached to a controller but I would not be surprised if you could get away with a plain old voltage regulator and a thermometer. I have used this many times to heat unusual shaped vessels or a flock of flat-bottomed micro-vessels when I had more than would fit into a heating block.
Instead of using sand, its insulating properties can cause the mantle heating elements to superheat, has anyone used aluminum pellets (approximately 1/8" x 1/8" x 1/8")?
Can someone suggest which metal both I can use to achieve 290 deg C?
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