In an old post I saw a comment suggesting the use of copper BBs for an alternative to an oil bath when heating over a hot plate. In another comment
somewhere was the idea of an aluminum foil skirt to push the heat towards the flask.
In the spirit of such discussion, would it be possible to use steel turnings for the heat transfer medium and further insulating the flask? It would
definitely be cheaper than copper and safer than oil when dealing with volatiles and could also be easily preheated in an oven to reach reaction
temperatures more effectively. Rainwater - 31-7-2022 at 14:24
I don't like the beads because once you lift the rbf they move. I have found compressed steel or copper wool wrapped in insulation to be very
effective. Ive even considered casting an aluminum block but never done it.lithiumion656 - 31-7-2022 at 14:53
steel wool sounds like an even better option thank youteodor - 1-8-2022 at 02:43
Once I tried steel wool patches wrapped in aluminum foil but found them as pure thermal conductors. The best option in my opinion for heat conducting
media is a steel or copper chain which can be easily put around RBF and easily removed.
But this method creates the risk of fire in case of RBF crack because solid media will always have a much higher temperature than the temperature
inside the flask.
I think for any organic chemistry laboratory a heating mantle is an indispensable piece of equipment.Mush - 1-8-2022 at 11:22
steel wool sounds like an even better option thank you
Do note that steel is very different from aluminum and copper for this application. Copper conducts heat ~2x better than Aluminum, and maybe 10-13x
better than steel.
The greater the conductivity the lower the heat gradient between the dry/solid "bath" medium and the glass, and the lower the heat gradient between
glass areas at different distances from the heat generator (both of which will determine the stress on your glass, the maximum safe effective
temperature you can use, the aging of your glass and the risk of cracking during operation).
A hybrid solution can be a good approach, whereby bigger pieces of high conductivity material (Cu/Al) are used in conjunction with a filler (for
instance, Bi, or a Bi/Sn alloy depending on desired fusion point) which reduces localized gradients by filling the void in terms of glass to metal
contact and thus also greatly increasing contact area. At lower temperatures it serves to hold the high conductivity pellets/beads/whatever together
in a solid mass, which avoids the annoying issue mentionned by Rainwater (note that Bi is a fairly rare element in that its volume slighly shrinks
uppon heating).Rainwater - 4-8-2022 at 04:05
True copper is better than steel, but steel is more accessible in the form of wool. In a perfect situation, a submerged heater would be best for
heating liquids, and liquid mercury for a warming bath. At this point, it depends on your needs. wants, and abilities.
But if it becomes an issue of convenience, a heating mantle is the professional approach for lab-scale reactions
.
I love my hot plat stirrer, for 0~100c (< 250ml) open-air reactions
For anything over 250ml or requiring a vacuum/controlled atmosphere, then I switch to a 2L mantel with insulation on top for extra ummp.
For designed applications, it all depends on what youhave on hand that can be made to work.PirateDocBrown - 4-8-2022 at 07:42
Aluminum shot is much easier on your glassware than copper or steel. Pushing a flask into a dish of it is far easier than the others. It's also fairly
cheap.Texium - 4-8-2022 at 09:27
Maybe compressing some copper scrub pads would make a decent heating medium.Mateo_swe - 11-8-2022 at 01:36
Why you want to use an alternative to an oil bath, to heat to higher temperatures?
Some good silicone oil can be reused many times and is easily found online.
If not using oil i would try small aluminium balls as they must be easier to use due to their light weight and aluminium is good for heat transfer and
pretty cheap.lithiumion656 - 11-8-2022 at 10:29
Fortunately, I happened across a well-priced 1000mL heating mantle with stirring, so I no longer need need this. However, I definitely will experiment
with the options presented here and discuss results once I have them. teodor - 11-8-2022 at 10:51
Congrats!
In one famous old book about organic experiments (50s or 60s), oil baths already were mentioned as "old school".
And I believe combining a heating mantle of any size with an external magnetic stirrer is not so extremely hard ... BromicAcid - 11-8-2022 at 14:10
Oil baths have their place, even still in industry. They come in great use for dealing with compounds that have a narrow thermal margin of safety as
they prevent major hot spots.Sulaiman - 11-8-2022 at 20:15
I like electric heating mantles,
I have a commercial 5l mantle that was donated to me,
and a diy 500ml mantle (cheap and simple - if you are comfortable with a little diy and electrical wiring)
Water and oil baths are useful,
for higher temperatures I use either a mantle or a hot air 'bath' made of a cylinder or inverted cone of aluminium foil over an electric hotplate or
gas flame.
In all cases, stirring is beneficial. Texium - 11-8-2022 at 20:39
I like oil baths specifically when used on a good hot plate with a temperature probe. I think they provide the most even heating and highest
sensitivity. I’ve witnessed aluminum bead baths have pretty bad hot spots leading to partially burnt reaction mixtures.pneumatician - 21-8-2022 at 17:37
Sand bath with oil or water.
Iron filings is another option... but if you want magnetic stirring... :-)
thank you