Sciencemadness Discussion Board - Sand baths

Sand baths

Ramblesthegoat - 3-3-2012 at 18:02

Hey guys, I have noticed that almost everybody (on Youtube at least) uses mineral oil baths for heating flasks and other things more evenly, but why do I never see sand baths? They are very cheap, reusable, can get to much higher temperatures, and in most cases less messy. Are they more dangerous or significantly less efficient? This might be a really dumb question and the answer is right in front of my face but this has been bugging me for a while.

entropy51 - 3-3-2012 at 18:18

Quote: Originally posted by Ramblesthegoat

Hey guys, I have noticed that almost everybody (on Youtube at least) uses mineral oil baths for heating flasks and other things more evenly, but why do I never see sand baths? They are very cheap, reusable, can get to much higher temperatures, and in most cases less messy. Are they more dangerous or significantly less efficient? This might be a really dumb question and the answer is right in front of my face but this has been bugging me for a while.

Click on the "Search" icon in the upper left hand corner. Enter "sand bath" in the search box. Select "Subject only" and "All forums". You will get several hits.

You can also search for subjects such as "heating" or "baths" and so on and find other hits.

If you are really diligent, you can even download several of the practical chemistry lab manuals in the forum library where heating methods and other techniques of the fine art of chemistry are discussed at length.

Wasn't that easy?

Ramblesthegoat - 3-3-2012 at 18:39

Well I guess I was more looking for advantages and disadvantages of sand and oil baths. I understand how to set one up and stuff, but I haven't found why exactly sand baths seem to be so unpopular. Is it because they can scratch the flask?

Funkerman23 - 3-3-2012 at 18:46

Quote: Originally posted by Ramblesthegoat

Well I guess I was more looking for advantages and disadvantages of sand and oil baths. I understand how to set one up and stuff, but I haven't found why exactly sand baths seem to be so unpopular. Is it because they can scratch the flask?

That( although hat is a minor concern) and simply because it is messy. At least that is why I don't use sand baths often. Frankly I prefer my Heating mantle but barring that a hotplate , crystallizing dish and the right oil are a good second best. But there are a lot more learned than I here.

Bot0nist - 3-3-2012 at 19:08

I use brine water baths, oil baths, and sand baths. Each in different heating temperatures and situations. I have even used small copper coated shot (BBs) lately a lot, as they have good thermal conductivity and they don't scratch. The method of heating should be tailor fitted to the reaction and apparatus.

zoombafu - 3-3-2012 at 22:34

One disadvantage of a sand bath is that it takes much longer to heat up than a mineral oil bath. However if you put the container with the sand in the oven, this will heat it up faster than using a hot plate.

bfesser - 3-3-2012 at 22:34

Sand baths suck. They're messy, they're very slow to heat and cool, and they're opaque. It's also not possible to just lower a clamped setup into a sand bath. You have to dig, shake, or aerate. There are so many better alternatives; heating mantles, water baths, metal shot baths, and baths of various oils. You can even use an ionic liquid or eutectic alloy if you're adventurous and reactivity isn't an issue.

[edit]
Sorry, forgot some classics: naked flame & heat gun

[Edited on 3/4/12 by bfesser]

MyNameIsUnnecessarilyLong - 4-3-2012 at 00:46

Quote: Originally posted by bfesser

You can even use an ionic liquid or eutectic alloy if you're adventurous and reactivity isn't an issue.

I once heard of people even using molten potassium nitrate for achieving high temps higher than 300C. That always sounded a bit dangerous and wasteful to me. But supposedly after the nitrate cools it will simply crack and flake off the flask so you don't need to wipe any messy oils off.

paulr1234 - 4-3-2012 at 01:20

Sand baths can be useful in some situations: http://curlyarrow.blogspot.com/2011/03/sand-bath-alternative...

ldanielrosa - 4-3-2012 at 01:30

I use a dedicated crock pot filled with sand to heat evaporating dishes (okay, mason jars)

Endimion17 - 4-3-2012 at 03:59

Quote: Originally posted by bfesser

[edit]
Sorry, forgot some classics: naked flame & heat gun

[Edited on 3/4/12 by bfesser]

Nakes flames are not a classic and never were. They should never be used for heating borosilicate flasks... unless doing some flameworking.

Heat gun is ok, if the temperature is not too high.

Anyway, there aren't methods that fit all the needs...

Ramblesthegoat - 4-3-2012 at 04:10

So it seems to me like sand baths are better for higher temperatures, but bad with heat transfer and spills are a pain. I will try some metal bb's because they seem to be the way to go, but different baths are good for different situations and temperatures. Thanks for all the advice guys!

BromicAcid - 4-3-2012 at 06:35

I've said it in other threads and I'll say it again. If you ever read the instructions for your hotplate it will usually have a warning about sand baths. Sand is a very good insulator and hence the instructions will warn you not to use sand baths for high temperatures as the insulating effect can burn out the coils. Since most people only want to use sand for higher temperatures this means that the utility of a sand bath becomes next to nothing.

This information is not just in the manuals, my hotplate has the same warning written on the tag on the cord not to go above 3 / 10 when using a sand bath and it was mentioned a few times during my college years.

Edit: Of course all of this assumes you want to use a sand bath on a hotplate. They work well to diffuse the heat of an open flame.

[Edited on 3/4/2012 by BromicAcid]

Bot0nist - 4-3-2012 at 06:41

I think peach, or somebody here, melted there hotplate by covering it tightly with foil. The heat built up inside the plate and destroyed it.

[Edited on 4-3-2012 by Bot0nist]

bfesser - 4-3-2012 at 09:27

Quote: Originally posted by Endimion17

[Naked] flames are not a classic and never were. They should never be used for heating borosilicate flasks... unless doing some flameworking.

I disagree. Although, perhaps, I shouldn't have said naked flames. If you're heating a florence flask with a non-flammable liquid, for example, you'd typically want to put a ceramic coated wire mesh between the flame and the flask. But it's not always necessary. Especially if the flame is low, and you're heating gently.

<hr width="300" />
I have a personal hatred of sand baths. The ceramic top of my favorite hot plate cracked cleanly in half because I was slowly heating a small sandbath. Even if you're careful, which I was, they're a pain. If you do choose to use a sand bath, as some procedures implicitly call for, be very careful. And don't use a ceramic top hot plate!

I forgot to mention a good one: steam baths/cones.

Bot0nist - 4-3-2012 at 09:32

I also use "air" baths to good success. All that's needed is a foil skirt around the RBF. lower it until in is just a few cm from touching the hotplate. Works fine for many lower boiling point refluxes and distillations.

Hexavalent - 4-3-2012 at 13:31

I also hate sand baths. Many of my expensive flasks have been severely scratched using them - personally, these days I use liquid paraffin/paraffin oil or sunflower/corn oil bath, the former which I buy in glass bottles from the pharmacy for treating diarrhoea(!) and the second, of course, from the supermarket, both very cheaply.

I have never tried mini copper BB pellets, although I may give them a go in the future. I am however, a big fan of air baths using aluminium foil (the Baco-foil thick stuff is the best).

My two cents, for all its worth

entropy51 - 4-3-2012 at 14:48

Quote: Originally posted by Endimion17

Nakes flames are not a classic and never were. They should never be used for heating borosilicate flasks... unless doing some flameworking.

Well that is news to all of us who learned organic back in the 1960's when Bunsen burners were the only heat sources used in the undergrad labs, including organic chem. Not to mention to guys like Liebig, Wohler, Hoffman, Perkin, Gatterman, Fischer and so on.

Flame free labs are a relatively new phenomenon.

So I think the Bunsen flame is indeed classic, if sometimes a little risky.

I have about 8 mantles, 2 stirring hotplates and several oil baths but I still sometimes use a Bunsen flame if I want to be able to immediately remove the heat at the first sign of trouble. (But I do always feel a little naughty when the solvent is flammable,)

Magpie - 4-3-2012 at 15:33

I don't think I've ever used a sand bath. Setting up a mantle seems so much easier. If I think I need an even heating high temperature bath I use silicone oil. If I need it even and kept below 100° I use a steam bath (especially good for low boiling flammable solvents like ether). I also use a Bunsen burner if I need heating with a quick response, and always use a screen with the ceramic center, unless just spot heating the glassware. My wife recently gave me a hot air gun for Christmas, and I'm finding I use that more than expected. It is the only heater I would use for certain applications.

Endimion17 - 5-3-2012 at 04:43

Quote: Originally posted by bfesser

I was referring to the process of heating a flask with visible flame (the hotter it is, the greater the danger), i.e. immersing it into the flame. That is something that should never be done. It doesn't have to crack at all. It just introduces stress inside the glass, and if you do it again, and again, and again, the stress builds up and one day CRACK, or if ether is inside, WHOOSH/BANG!.

It is a rule. Period.

Quote: Originally posted by Bot0nist

I also use "air" baths to good success. All that's needed is a foil skirt around the RBF. lower it until in is just a few cm from touching the hotplate. Works fine for many lower boiling point refluxes and distillations.

Yeah, that's a convenient way, too, though it isn't recommended it for things like ether. Non-flammable halogenated hydrocarbons, that's ok.
If the flask cracks, and they do occasionally, ether will fall on the hotplate and catch fire. Such fires are quite spectacular.

It's always better to use a water bath for ether, as it boils at around 36 °C.

Foil skirt or not, it's always bad to lower the flask to the metal of the heating pad, but if the setup is heavy, and you don't want to clutch it too hard with clamps, you can put a small cushion of asbestos mat (2x2 cm) between. Asbestos is soft, so this works great.
Sometimes I do it with 4 cushions, placed at four corners, like here.

Quote: Originally posted by Hexavalent

I also hate sand baths. Many of my expensive flasks have been severely scratched using them - personally, these days I use liquid paraffin/paraffin oil or sunflower/corn oil bath, the former which I buy in glass bottles from the pharmacy for treating diarrhoea(!) and the second, of course, from the supermarket, both very cheaply.

I have never tried mini copper BB pellets, although I may give them a go in the future. I am however, a big fan of air baths using aluminium foil (the Baco-foil thick stuff is the best).

My two cents, for all its worth

Sunflower oil fan right here!

I heated it to 280 °C. No smoking occured. Great stuff.
Paraffin tends to smoke and catches fire rather easy if you go that high.

Quote: Originally posted by entropy51

I doubt the mentioned guys were stressing their equipment like that.
The heat of the naked flame was always used together with an asbestos mat, or a bath of some kind.
One of the rare things that can be immersed into a naked, blue flame are thin porcelain crucibles, after they were preheated above the sooty yellow safety flame for a few minutes.
And of course, quartz vessels can be immediately heated in the blue flame.

You're playing with the devil. Keep building stress in the glass and one day an accident will happen...

bfesser - 5-3-2012 at 17:02

Seeing as the original post's questions have been thoroughly answered, discussed, and elaborated upon at this point; I see no harm in taking this thread a little more off topic.

Quote: Originally posted by Endimion17

You're playing with the devil. Keep building stress in the glass and one day an accident will happen...

Says the man who experiments with large volumes of liquid mercury, causes white phosphorus to luminesce, images mercury vapour with ultraviolet lamps, dips his fingers in molten lead, intentionally starts mock laboratory fires, microwaves assorted metallic and glass objects, surfs on elevators . . . need I go on?

I don't think your opinion has much value. The fact is that naked flame is a classic heating method, even for borosilicate glassware. Flame heating has been associated with chemical (or material, elemental, phlogistical, whatever) manipulations since pre-Lavoisier chymistry and even alchemy. Besides, I never said that flame heating was superior, simply that it's a classic.

I'd like to add that, from my personal experience (which I'm sure mirrors that of others here), vintage borosilicate glassware, although it is typically thinner-walled and of lighter construction, will take more abuse than it's modern day equivalents. I've dropped old 'green stamp' 500 ml Erlenmeyer flasks from shoulder height to a rough concrete floor and watched them bounce at least a meter into the air and continuing until at rest with no damage observed whatsoever. These flasks were heavily used before they ever came into my posession--with FLAME! Try doing that with your 'unstressed' glassware. Your arrogance does not lend support to your opinion, nor does it cause reality to reflect your opinion.

<a href="http://www.ch.ic.ac.uk/video/linstead/" target="_blank">[video featuring classic organic chemistry utilizing flame heating]</a>

entropy51 - 5-3-2012 at 17:17

Quote: Originally posted by bfesser

I'd like to add that, from my personal experience (which I'm sure mirrors that of others here), vintage borosilicate glassware, although it is typically thinner-walled and of lighter construction, will take more abuse than it's modern day equivalents. I've dropped old 'green stamp' 500 ml Erlenmeyer flasks from shoulder height to a rough concrete floor and watched them bounce at least a meter into the air and continuing until at rest with no damage observed whatsoever.

I can second that. Some of my Pyrex is older than I am and has seen many a flame applied.

I think it is the rate of temperature change and not the heat source that causes glassware to fail.

I have to shake my head when I read about some of the "unexpected" catastrophic glassware failures that people report on the forum.

Endimion17 - 6-3-2012 at 00:48

Quote: Originally posted by bfesser

Seeing as the original post's questions have been thoroughly answered, discussed, and elaborated upon at this point; I see no harm in taking this thread a little more off topic.

Says the man who experiments with large volumes of liquid mercury, causes white phosphorus to luminesce, images mercury vapour with ultraviolet lamps, dips his fingers in molten lead, intentionally starts mock laboratory fires, microwaves assorted metallic and glass objects, surfs on elevators . . . need I go on?

I see no problems with those experiments. They were done with a great deal of ventilation, and sometimes mask was used. Mock fire was made in an almost completely empty room made of concrete, with one wooden shelf and a water main exactly behind the camera. Molten lead is a trick, and so is the elevator surfing. Microwaving a CFL immersed in a glass of water is one of the safest tricks you can do with such oven.

Quote:

I don't think your opinion has much value. The fact is that naked flame is a classic heating method, even for borosilicate glassware. Flame heating has been associated with chemical (or material, elemental, phlogistical, whatever) manipulations since pre-Lavoisier chymistry and even alchemy. Besides, I never said that flame heating was superior, simply that it's a classic.

I'd like to add that, from my personal experience (which I'm sure mirrors that of others here), vintage borosilicate glassware, although it is typically thinner-walled and of lighter construction, will take more abuse than it's modern day equivalents. I've dropped old 'green stamp' 500 ml Erlenmeyer flasks from shoulder height to a rough concrete floor and watched them bounce at least a meter into the air and continuing until at rest with no damage observed whatsoever. These flasks were heavily used before they ever came into my posession--with FLAME! Try doing that with your 'unstressed' glassware. Your arrogance does not lend support to your opinion, nor does it cause reality to reflect your opinion.

<a href="http://www.ch.ic.ac.uk/video/linstead/" target="_blank">[video featuring classic organic chemistry utilizing flame heating]</a>

On the other hand, heating a glass vessel with a naked blue flame will introduce stress buildup. That's a fact mentioned in pretty much every lab manual I've read, and it's something glassblowers/flameworkers always talk about when asked about the chemists' worst habits (that, and stucked glass joints). They usually do an assortment of facepalms while discussing it.

Thinner glass or thicker glass? It depends. For new glass (boro 3.3) thicker is the option. Old Jena glass (boro 3.1 I believe) prefers thinner. Nobody works with 3.1 anymore, and if you have a broken part, repairing it is a nightmare.

You think your flask that fell on the floor is safe as ever? Sorry, but you really don't know much about glass. I don't, but you know way less.
Flasks that fell on the floor and managed to survive have either microfractures or local stress. They're prone to bursting more than a brand new.

If I'm arrogant, then my flameworker is arrogant, too. I'm just repeating his words.

@entropy51: It's not just the temperature change rate, but the geometry of heating. There's a reason why mantles and baths exist.

[Edited on 6-3-2012 by Endimion17]

Mumbles - 6-3-2012 at 01:52

I use sand baths on occasion. Back with my homelab, I'd use them to do some moderately high temperature reactions. I didn't have access to good silicone oil at the time. I wish I had known about sunflower oil back then. In the academic lab I currently work in we use sand baths to activate things like silica and alumina. The temperature we activate them at (250C) is on the upper end of the useable range of even the high temp silicone oil and much cheaper.

bfesser - 9-3-2012 at 09:57

Quote: Originally posted by bfesser

<a href="http://www.ch.ic.ac.uk/video/linstead/" target="_blank">[video featuring classic organic chemistry utilizing flame heating]</a>

Sorry, I noticed that this video doesn't seem to load from the original site. I've uploaded the film segment to YouTube.

http://www.youtube.com/watch?v=5PcrVsYxAYs

Magpie - 9-3-2012 at 10:12

Wow. Don't you just love the casual attitude and agressive heating of these old cehmists? No safety glasses or closed sash (but does have lab coat, albeit open). I love the pipe smoking at the end. Just another day at the lab.

I watched a fun old movie last night on the TMC channel. The story took place in Glasgow, Scotland in 1857. A woman accused of murder was shown washing her hands in "Prussic acid" that had been poured into a wash basin of water. Later she bought some arsenic at the local pharmacy to use as a cosmetic on her face. Yikes!

How times have changed. The movie was made at Pinewood Studios but I came in late so don't know the name of it.

Edit: It was "The Madeleine Smith Story," apparently a very famous event in Scotish judicial history. The movie is based on an actual event.

[Edited on 9-3-2012 by Magpie]

[Edited on 9-3-2012 by Magpie]

daragh8008 - 28-6-2012 at 05:57

Quick side track. My new hydrothermal reactor arrived today (http://www.col-int.com/hydrothermal-reactor-cithtc230v50-p-2...) I was going to stirr it using a little magnetic stirrer on my hot plate in an oil bath for temperatures around 150C. Would this be more suitable than sand? I hate using oil because the oil bath oil I have is horrible to clean off but I figure the temperature would be alot more even. Also I wouln't be able to insert a thermometer into the vessel so I will only have the bath temperature to go by. Any options??

watson.fawkes - 28-6-2012 at 07:08

Quote: Originally posted by daragh8008

I was going to stirr it using a little magnetic stirrer

I noticed that the alloy is a nickel one. Many (most?) such alloys are magnetic themselves. Are you sure that you can run a magnetic stirrer through it?

daragh8008 - 28-6-2012 at 11:02

Um... I was until I was your post. Not so sure now though. I guess it will be a case of try and see. I can stir through the steel bowl of oil but at low temps when the oil is very viscous I have to make sure the bowl is clamped or it will spin too. But I assume that this is due to the oil dragging the steel. I have know idea of the alloy of the bowl though. I guess I'll find out soon enough is I can stir through the reactor.

daragh8008 - 29-6-2012 at 16:21

Well an oil bath is out. The reactor comes with a removable base which looks as if the oil could leak through to the Teflon liner. I guess unstirred and in the oven is the only option

daragh8008 - 3-7-2012 at 04:23

Ok so I have had time to play with my new toy. It can be stirred by placing a Teflon coated stirrer bar inside the vessel and placing it on a hot plate. However I didn't go down that route as I didn't think the heating would be even. Instead I used my oven to heat it as per the manufacturers instructions. Turns out stirring was not required for my experiments as the sol preparation worked first time just fine.

valekovski - 12-12-2016 at 05:27

Hi

I know this is an old post but I stumbled upon it googling for sand bath alternatives.

And I have been thinking and figured, why not use aluminium foil? Either pack it in (instead of the sand) or, I also noticed that grinding the foil in a coffee grinder for a couple short bursts (a second or two) isn't enough to powderize anything, but sort of makes these little ball-like chunks.

Al has a great thermal conductivity (might need some insulation so as not to loose heat too quickly...) and is pliable, so a RB flask can just be shoved in there

Has anyone tried that? Or can someone tell me why this would NOT be a good idea?

Thanks! Cheers,
Val

[Edited on 12-12-2016 by valekovski]

brubei - 12-12-2016 at 06:34

Quote: Originally posted by valekovski

Hi

I know this is an old post but I stumbled upon it googling for sand bath alternatives.

And I have been thinking and figured, why not use aluminium foil? Either pack it in (instead of the sand) or, I also noticed that grinding the foil in a coffee grinder for a couple short bursts (a second or two) isn't enough to powderize anything, but sort of makes these little ball-like chunks.

Al has a great thermal conductivity (might need some insulation so as not to loose heat too quickly...) and is pliable, so a RB flask can just be shoved in there

Has anyone tried that? Or can someone tell me why this would NOT be a good idea?

Thanks! Cheers,
Val

[Edited on 12-12-2016 by valekovski]

Metals will oxidise and generate an insulation layer on the particles surface.

Graphite powder is good enough thermal conductor to be used as sand bath. We use it at my lab.

Sulaiman - 12-12-2016 at 06:57

I quite like using a sand bath - because I've been using a small and large one of these solder pots
http://i.ebayimg.com/images/g/uWEAAOSw6n5XuboD/s-l500.jpg
and if oil spills it smokes whereas dry sand is so easy to clean up.

I think that an intense blue flame in one spot to heat glassware is reckless,
but sensible use of an open flame was the basis of alchemy - with soda glass.
Thinner glass should survive thermal differences better than thicker glass which is for clumsy people like me.

EDIT: If you regularly use an oil bath it is likely that the same flask is heated to the same depth repeatedly, consistently.
would that not stress the glass more than the heating gradient within a sand bath ?
P.S. I've not done enough experiments to have glassware break in use (plenty in cleaning or 'storage')
so with no 'panic mode' experience, my opinion is of little value here.

[Edited on 12-12-2016 by Sulaiman]

careysub - 12-12-2016 at 08:44

Quote: Originally posted by brubei

Quote: Originally posted by valekovski

Has anyone tried that? Or can someone tell me why this would NOT be a good idea?

Thanks! Cheers,
Val

[Edited on 12-12-2016 by valekovski]

Metals will oxidise and generate an insulation layer on the particles surface.

Graphite powder is good enough thermal conductor to be used as sand bath. We use it at my lab.

I imagine you brought up oxidation layers by analogy with electrical resistance, where an oxidation layer can have a large effect on electrical conduction. The electrical resistance (or conductance) of aluminum oxide for example differs by 22 orders of magnitude from aluminum metal.

But the thermal conductivity of aluminum oxide is only 1 order of magnitude lower.

Unlike electrical conduction there are no really good thermal insulating materials so very thin layers of anything will have little resistance to heat transfer. Electrical conduction of solid materials can vary over 32 magnitudes (copper to PTFE), but thermal conductivity by less than 3 magnitudes.*

So the oxide layer on a metal like aluminum or copper will be insignificant with respect to thermal conductivity since it is extremely thin.

The little ball-like chunks will be mostly hollow (I expect) and airspace is an insulator. You want a solid, close packed material to conduct heat. Aluminum -pellets/granules/shot/shavings/chips are very good and can be had relatively cheaply (pellets are 10 lb for $50 on eBay, also try shavings which are about $4/lb).

Copper chops can be had on eBay for $4-5/lb also, and it is the best conductor (this stuff is electrical grade, high purity, which makes it the best conductor available that is cheaper than silver). But copper is 3 times denser than aluminum so three times as much is needed to fill a bath.

Graphite flakes or powder can be an excellent thermal conductor. Annoyingly it is hard to get an estimate on an "average" graphite powder by Googling. Graphite is highly anisotropic, and is an excellent conductor along the crystal plane, but a good insulator across it, so most sources hem and haw and give a 20-fold range for what the conductivity might be. Also graphite is famously messy to work with, black smears get on everything and are hard to wash off.

You can also mix materials to make a bath - a more expensive fine material with cheaper coarse one for example.

*If you look up thermal insulators you will find that all decent insulators are actually porous, relying on air to do the insulation since no solid is very good at it.

[Edited on 12-12-2016 by careysub]

careysub - 12-12-2016 at 09:44

Quote: Originally posted by valekovski

Al has a great thermal conductivity (might need some insulation so as not to loose heat too quickly...) and is pliable, so a RB flask can just be shoved in there

Has anyone tried that? Or can someone tell me why this would NOT be a good idea?

The air space in the aluminum balls is an excellent insulator, so the thermal conductance over all will be poor.

Shoving flasks into sand (or metal) baths is a poor procedure. You should clamp the flask positioned in the empty bath, then add the packing material around it. Easier, and less glass scratching.

[Edited on 12-12-2016 by careysub]

valekovski - 12-12-2016 at 15:12

You guys are the best, great points were made. Thanks!

As for "shoving the flask in the media", that was just my poor expression, I actually do pack the media around

I will most likely be trying several of the mediums suggested and will let you know how it goes when I get to it.

Cheers, Val

Dr.Bob - 12-12-2016 at 19:35

I have used sand baths, they are OK for a few uses, but generally a mess and hard to get flasks into. They do work well with small vials and test tubes, if you are doing several small reactions. Another useful heat source is a dry heating bath, the biologists use them often for PCR, media growth, incubation, and much more. I use them for vials and tubes also, great for small arrays of reactions, or testing multiple copies of the same reaction with different solvents, catalysts, bases, etc for process type work, or DOE optimization of a synthesis.

But oil baths and heating mantles are my favorite means. Much comes down to what you do and the budget. If you heat mostly the same size of flask, a heating mantle is ideal, but if you do a lot of various sizes and flask types, oil baths are very useful, and you can even do a few reactions at once, and you know that they all had the same temp (also useful for process work).

MrHomeScientist - 13-12-2016 at 13:38

Sand baths also run the risk of damaging your hot plate, since it isn't a great thermal conductor. This happened to me recently - the hot plate still works, but the surface is filled with small cracks now.

"Lab armor" is a product that I'd like to try. It's just aluminum bits (sort of flattened disks) and is actually very overpriced for what it is, but you can request a sample on their website (I've tried a few times and got no response, though). Seems like something that would be simple to make.

careysub - 13-12-2016 at 13:53

Quote: Originally posted by MrHomeScientist

Sand baths also run the risk of damaging your hot plate, since it isn't a great thermal conductor. This happened to me recently - the hot plate still works, but the surface is filled with small cracks now.

"Lab armor" is a product that I'd like to try. It's just aluminum bits (sort of flattened disks) and is actually very overpriced for what it is, but you can request a sample on their website (I've tried a few times and got no response, though). Seems like something that would be simple to make.

The aluminum pellets I mention above on eBay are a reasonable, much cheaper, substitute. They are short cylinders (cut wire pieces) instead of the Labarmor M&M shapes which are optimal* but a little tumbling with sand should take off any sharp edges.

*There is mathematical proof of this. See attached paper.

Attachment: M&M.pdf (295kB)
This file has been downloaded 2805 times

valekovski - 13-12-2016 at 14:01

MrHomeScientist, I know what you mean, mine isn't doing too well either

I think I might start by trying a mixture of small copper nails that I have lying around and sand to fill in the gaps, see how it goes... It should improve conductivity, not sure by how much tho. Haven't been able to find an exact equation for thermal conductivity of two solid mixtures, at least not a one that I could decipher quickly. Perhaps I can put some aluminium foil on the bottom of the flask to minimize scratching. The biggest challenge might be to get a homogeneous mixture of nails and sand. Hopefully there won't be any major cold spots which might cause a crack...

I did have another idea tho. Graphite powder sounds way too messy, but what about a solid chunk? I have seen these hotplate "reaction blocks" made out of aluminium, like this one: http://www.wilmad-labglass.com/Products/LG-18900083/. Expensive little things. So I've been thinking, why not make one out of graphite? Solid blocks go pretty cheap on ebay and it could be shaped like the "reaction block" above pretty easily. Just get a flask-sized ball and drill into the block? Have not found any products like that...

[Edited on 13-12-2016 by valekovski]

[Edited on 13-12-2016 by valekovski]

careysub - 13-12-2016 at 14:24

There are also a variety of granulated/flaked/powdered aluminums available from Firefox-FX for $4.75-$15/lb depending on how much and what grade.

This could be used alone, or mixed with cheap aluminum scrap/pellets to fill in the voids and enhance conduction.

Due to a court injunction placed against Firefox-FX years ago their very fine aluminum powders require an ATFE license to purchase (but similar powders are available from other pyro firms without a license), but it is their coarser, cheaper "No ATFE" aluminums you would want anyway.

valekovski - 14-12-2016 at 00:41

I would not use aluminium powder for that... It's messy, a potential fire hazard, not to mention breathing the dust is toxic afaik...

PS: Not to be a jerk, but please use aluminium instead of "aluminum", it feels like a splinter in my brain every time I hear it

MrHomeScientist - 14-12-2016 at 07:22

IUPAC says both are acceptable!

You could write a browser add-on that adds the extra 'i' to aluminum if it bothers you that much. While you're at it, add scripts for 'sulphur' and 'caesium' too.

careysub, that pdf was very interesting. Thanks for sharing.

careysub - 14-12-2016 at 07:49

Quote: Originally posted by valekovski

I would not use aluminium powder for that... It's messy, a potential fire hazard, not to mention breathing the dust is toxic afaik...

PS: Not to be a jerk, but please use aluminium instead of "aluminum", it feels like a splinter in my brain every time I hear it

I am sympathetic to the aluminium cause, at least Americans have almost entirely stopped using "columbium" (even though that name does have legitimate priority, it isn't what IUPAC blessed). I see the USGS was still using columbium in 2000 as the primary name:
http://minerals.usgs.gov/minerals/pubs/commodity/niobium/230...

But us Americans are ourselves trapped in the "aluminum-verse" so it is a habit. IUPAC does allow "aluminum" (as a sop to us) but it is inconsistent with other element names. Getting non-chemists to use it here is as likely as getting them to abandon the US Customary system of units.

Yes, you would NOT use aluminum POWDER - it is messy (similar to graphite powder in fact) and a fire hazard, I am suggesting coarser aluminum preparations as an option, flakes, and various granulated forms as possible materials. I have "flitter" flakes (10-12 mesh) that I think are suitable for example. 50-100 mesh granular/flake may be OK (not sure, I don't have any to inspect).

The pellets are better, but adding a coarse filler to the pellets (which is smaller than the pellets) should improve heat transfer even more.

[Edited on 14-12-2016 by careysub]

careysub - 14-12-2016 at 08:22

Quote: Originally posted by MrHomeScientist

careysub, that pdf was very interesting. Thanks for sharing.

You're welcome! There is actually a formal publication on this (see attached), but I thought the one I used was more informative over all.

Attachment: Donev_et_al_Science_M&M.pdf (564kB)
This file has been downloaded 397 times

valekovski - 16-12-2016 at 15:56

So here is my initial setup and results. I used copper nails and beach sand and wrapped the flask in aluminium foil (just to minimize scratching). See attachments for pics.

I started at about half the power for the first 15 mins and then crank it up to full. Heating element is supposed to be 1500 W. The last pic is a measurement taken about 12 mins in. The difference between top and bottom layer is about 30 degrees centigrade. The temperature gradient remained pretty constant throughout the process and settled at about 50 C top to bottom. There were some "hotspots", ie. the temperature on the surface varied depending on the side I took the measurement on. Max difference was about 20 C.

It took me 45 mins to bring about 300 ml of water to a hard boil. I turned the hotplate off immediately after it started boiling and it continued to boil for 15-20 mins. Before I went to bed, about an hour later, the entire setup was still very hot.

Observations and assumptions:
* I expected aluminium foil to cause air pockets between the foil and the flask. I was afraid it might crack the glass if a part was too insulated from the rest. Turns out that the weight of nails/sand packing snugs the foil quite nicely to the flask. I don't think there are significant air pockets.
* The whole process still took annoyingly long... But the temperature gradient was much lower between top and bottom layers than it was with just the sand packing! Although still taking a long time to heat up sufficiently, it is still quite faster than a pure sand bath. Pure sand bath took me well over an hour to boil the same amount of water.
* I think I should be able to crank up the heat to full power right from the start to speed up the heating a bit. I think the 50 C max difference in temperature between top and bottom is acceptable so as not to cause thermal shock to the flask.
* Although having a lot of copper in the packing and heating up faster than a sand bath, it retains heat very well. Honestly, I expected it to go cold in half an hour.
* I think I can improve efficiency or rather the time it takes to heat it up. Mainly by taking better care when packing the bath. First, nails have caps. According to the article on improving packing with ellipsoids you've provided, I should improve packing by taking of the caps or just cut some thick gauge copper wire. I think that would improve the temperature variation on the surface of the bath, which was probably caused by uneven packing. I think I might put some glass wool on the surface as well to retain the heat a little more.

Hope this info helps someone.

PS: I still want to try the graphite block idea, but having a little trouble finding a ball burr bit the size of a flask

[Edited on 17-12-2016 by valekovski]

Refinery - 15-5-2020 at 07:19

Could gallium be good for heating bath?

mackolol - 15-5-2020 at 10:52

Quote: Originally posted by Refinery

Could gallium be good for heating bath?

For sure it would be damn expensive. Better try Wood's Alloy, which is cheaper, It's sometimes mentioned in syntheses.

Fyndium - 16-2-2021 at 05:38

Looks like sand bath is the best and only suitable heating method for delrin pyrolysis which has upper temp cap of 420C. I'm gonna heat the bath with gas burner, because using any sort of hotplate seems very risky for the plate's well-being. I considered steel shot bath from smallest nuts available at bulk price, but sand likely produces smoother heating action for the specific reaction.

I have experience on trying sand and salt baths, and it appears that they are both very slow to heat up, and cannot deliver good heat transfer. This same phenomenon is noted when comparing oil bath to CaCl2 bath. Oil baths require easily 50C+ thermal gradient to boil stuff, while CaCl2 only 20C is usually enough. Sand baths seem to be a possible heating option for long run reactions requiring stable high heat above +200C, but not especially powerful heat transfer, which may limit their use for boiling high thermal capacity liquids like water, ethanol, etc which remove energy from reaction faster than sand can transfer it, unless so high thermal gradient is used it causes risk of glass failure. It also works for stationary reactions which need no thermal adjustment or which can be buffered using condenser without fear of runaway or side reactions at that temp, as the reactor cannot be effectively moved in or out of the sand. I believe pyrolysis fits this description well, as long as the contents are not prone to excess frothing. It avoids hotspots and yet delivers enough heat to decompose the substance in a controlled manner.

Texium - 16-2-2021 at 08:09

The organic chemistry stockroom at my university has been continually promoting the filling of heating mantles with sand. And they wonder why they have such a high failure rate! That doesn't fly in the sections that I teach. I will continue to wage my private war against them for the rest of this semester. Then I'll be done teaching and couldn't care less about how many perfectly good mantles they burn out...

Fyndium - 16-2-2021 at 08:42

Sand, dehydrated gypsum or even ceramic tiles are such good insulators they will burn even thicker gauge kanthal wire, I've experienced this so many times with my electric oven that I moved to propane heated after trying to mess with it.

I would absolutely never pour anything into heating mantle. Not sure about hotplates how they could be protected, possibly by using a thick steel plate as temp buffer/conductor between it and the sand bath? I'd got 20mm dumbbell plates 5kg each for this purpose. Air gap might not be any better, since air is the best insulator of all easily available materials after vacuum, in practice.

There are plethora of instances where open flames pose great fire hazard, so a closed circuit heating element for sand baths would be necessary. In my instance, I just make it case sensitive and use sand bath for +250C operations where I make the environment suitable for gas flame, and for anything below 200, oil bath with induction heater works best, and then there is also the heating mantle without any additives. My heating mantle is rated up to 400C, but I'm gonna go easy with it, don't want to burn the heating elements and likely never gonna hit above 200 with it.

Sulaiman - 17-2-2021 at 02:59

Open flames provide an obvious ignition source,
but the surface of a hotplate heating a sand bath will quite likely be above the autoignition temperature of common solvents - a not so obvious hazard.
PLUS, if a flask does fail it will dump the boiling liquid into the sand - which will be at a MUCH higher temperature than the already boiling liquid...
flash boiling!

What fool had the idea to put sand in a heating mantle?
Even a hobby chemist (like me) is not that dumb.

To distill concentrated sulphuric acid I recently used cheap Chinese glassware ABOVE (not in) a gas flame
(portable butane gas stove)
No matter how you heat glassware you should EXPECT it to fail and prepare for it,
if the glassware survives consider it a bonus.
(I've not had glassware break due to heating yet, but I do try to prepare for it)

Texium - 17-2-2021 at 08:25

Quote: Originally posted by Sulaiman

What fool had the idea to put sand in a heating mantle?

I don't know who had the idea, but it has infected the entire chemistry department at a major research university... I'm definitely going to have a chat with the stockroom manager. It's always refreshing to have what I take for common sense validated here.

Fyndium - 17-2-2021 at 08:47

Quote: Originally posted by Sulaiman

To distill concentrated sulphuric acid I recently used cheap Chinese glassware ABOVE (not in) a gas flame
(portable butane gas stove)
No matter how you heat glassware you should EXPECT it to fail and prepare for it,
if the glassware survives consider it a bonus.
(I've not had glassware break due to heating yet, but I do try to prepare for it)

I used to heat all glass with direct open propane flame or on metal hotplates when I was young and very reckless. I still say some good words that I never cracked a single glass; I smashed them only when cleaning or handling them otherwise, including dropping and entire operating distillation apparatus on the floor once. The most amazing part was that only the distillation head broke. Gosh, I get creeps thinking those times.

One should not trifle with safety, though. All it takes is one cracked flask half-full of low boiling solvent, and you have instant out-of-control fire that will burn down your entire house unless you have a large scale distinguishing capacity within hand's reach.

Sulfuric acid is one of these exceptions where I'd just use sacrificial glass and open flame, and put it in some sort of container than can limit the volley of boiling sulfuric acid if a catastrophic failure is to occur. When I vacuum distilled a little sulfuric acid from battery acid, I built a quick enclosure from plexiglas and plywood around the boiling flask in case of failure and kept a pressurized water hose at hand. I did this in a space with all-concrete surfaces where such a splash wouldn't cause too much issues.