I want to adopt a safe and reliable method of heating whatever vessel that needs heating and after a reasonable amount of research and trial and error
I've concluded that sand baths are the way to go. The only experience I have with them is in my universities lab performing microscale procedures so I
have plenty of uncertainties so am hoping that some of you here who are more experienced can share your knowledge.
Firstly the type of sand. I decided to cut open a sandbag that the city dropped off at my door a few months ago in preparation for a flood. This is
sand is not smooth at all, its rough and contains lots of stones, when I heat it up it smells of burning. I live near the beach so I could easily get
smooth sand with no stones. Would sand from the beach be the right kinda sand for a sand bath?
Another concern I have is the fact I don't have a temperature probe for my hot plate. At college all the hot plates have temperature probes which act
as thermostats meaning you the temperature of the sand bath will stop rising once it hits whatever maximum temperature you set for it. Without a
temperature probe will I have a rough time keeping the sand bath at a particular temperature?
Finally I was wondering if I should preheat the sand bath in the oven before use seeing as it may take a very long time heating a large pot of sand
with just a hot plate. A hot plate only transfers heat via the bottom of the sand bath and even with tin foil, allows great amounts of heat loss. An
oven on the other hand heats the bath from all sides and allows far less heat loss. I'm thinking the way to go would be to heat the sand bath in the
oven to around 10-15°C under the desired temperature then use oven mits to carry it out to the lab. magnus454 - 2-9-2011 at 18:58
Get yourself a bag of sandblasting sand, It's highly purified, and of uniform grain size to prevent clogging of the venturi or nozzel Bot0nist - 3-9-2011 at 03:25
Have u looked into using copper bbs for an air gun? I hear they work really well at heat transfer.Arthur Dent - 3-9-2011 at 04:52
@ CrimpJiggler :
I've been experimenting with sand baths for quite a while, and out of experience, I have noticed that slightly coarse sand works best. If the sand is
too fine, it will tend to stick to the glass vessel and make a mess while you're moving your flask away from the sand bath.
By coarse, I mean if you take a handful, you can see the individual sand grains and their colors, and the wet sand will feel gritty.
Now the trick to have sand that's "sand bath-ready" is to literally wash it! My technique is to take a large empty container, like a bleach bottle or
a plastic water bottle, fill it with sand about halfway and then fill it with lukewarm water. Shake the container thoroughly and then rapidly pour the
water out, just stopping before the sand starts coming out. You'll see a lot of silt, organic material, roots and crap come out with the water, which
will be a yellowish brown. Repeat as many times as necessary (5 or 6 times) until no soil and silt comes out and the water is clear.
You can then put your sand in a plastic sieve and rinse under tap water to remove the last bit of silt, and let it drip until it's a wet, solid mass.
The last step is the longest. Take a large stainless steel dish (large salad bowl) and line it with aluminum paper, throw the sand in clumps in the
bowl and set your oven at 210F (100 C) for about an hour, and increase to 450 F (220C) and leave it in there for 3 or 4 hours. This "sterilisation"
process is to ensure that you eliminate any traces of organics, and smoke out your sand (put the oven fan to max), and that your sand will be pefectly
dry. Failure to do that will result in smelly, smoking sand when you use it in your sand bath.
To use a sand bath effectively, you can use a small stainless steel bowl, fill it with sand, and then push down your vessel in the sand. Don't use a
glass bowl to put the sand in, this could result in catastrophic failure if your reaction boils over and touches the sand and/or the bowl. A cool
thing about sand baths is that if there is a little boil over and some of the solution falls in the sand, it will "clump" and you can pick the clump
away just like in kitty litter.
Technically, you don't need to monitor your sand bath temperature, as long as you monitor your reaction vessel temperature. A lab jack under your
hotplate is a handy way to take away your sandbath without disassembling all your apparatus.
Have u looked into using copper bbs for an air gun? I hear they work really well at heat transfer.
Good one, I didn't think of copper bb's. small ones would make an excellent and clean heat transfer medium. Copper stays pretty sterile as well too.D4RR3N - 3-9-2011 at 11:12
Depends how hot you want the sand bath but I once experimented with putting a bulb under a sand bath attached to a dimmer switch, is quite consistent
with its heat output.Endimion17 - 3-9-2011 at 11:59
Proper sand baths are made of steel vessels with quartz sand and can be heated with gas burners, otherwise they contain electric heating elements.
They are used for heating up to 360 °C. That's in my manual.
One of the best things is to take beach sand and remove the organics and calcium carbonate (shell debris, etc.). You can do it by boiling in
hydrochloric acid and then washing. Or, if you don't mind small pieces of carbon, heat it in a crucible, wash with HCl and water. Just remember to
wash it with water, because you don't want any salt inside.
Then sift if through a sieve to get more uniformed grains.
Sifted sand beach is much smoother, so when it's dry and very hot (way above the maximum sand bath temperature), it becomes relatively mobile and
similar to a liquid. That probably has something to do with poor heat conductivity and Brownian motion. I've observed "boiling" of fine sands on
several occasions, and if you vibrate the vessel, it will flow pretty much like a liquid, and it can spill out and burn you, so be careful.
This phenomena is one of the reasons why granular matter like is a special case in soft matter physics.
Here's a nice animation from one institute.User - 4-9-2011 at 01:53
A good practise is to use a sleeve to filter out the larger particles.
Myself I am always concerned with the scratching effect on my glassware.
The coppershot seems a very good idea.
Hell why not aluminum foil balls.Bot0nist - 4-9-2011 at 03:06
I've seen a member here use the copper shot. I can't remember who though, maybe redox or peach. Whoever it was they swore by it and that is what I use
now. It's way less messy than sand, doesn't scratch, and has great thermal conductivity.CrimpJiggler - 13-9-2011 at 11:44
A cool thing about sand baths is that if there is a little boil over and some of the solution falls in the sand, it will "clump" and you can pick the
clump away just like in kitty litter.
Thats certainly far more desirable to what happens when some of the flasks contents boil over and fall into a hot oil bath. Thanks for all the tips.
These will be a huge help to me. Are there any types of shops that sell these kinda jacks OTC or is it necessary to order them? I'd imagine jacks like
that have lots of uses, not just in chemistry.
I've seen a member here use the copper shot. I can't remember who though, maybe redox or peach. Whoever it was they swore by it and that is what I use
now. It's way less messy than sand, doesn't scratch, and has great thermal conductivity.
It was actually smuv, in the sodium tosylate-->p-cresol thread.
I need to get some bb's, they seem really convenient and clean. Lambda-Eyde - 13-9-2011 at 17:27
A nice tip to avoid scratching your precious round bottom flasks in sand baths: Cover the bottom with aluminium foil.Arthur Dent - 14-9-2011 at 03:58
A nice tip to avoid scratching your precious round bottom flasks in sand baths: Cover the bottom with aluminium foil.
Well I have to admit that your mileage may vary on that one. I did this once (twice actually) and the results were not what I expected.
First time was when I acquired my Fisher hotplate... being second hand and nearly antique, I decided to give it a good scrub down and it looked
fantastic when I was finished. Not wanting to waste my good work, I would put a piece of aluminum paper over the heating plate whenever I used it to
prevent spillage and staining. One one occasion, I had put a beaker directly on top of the aluminium paper-covered hotplate...
Catastrophe! The aluminium paper partially melted and created super hot spots on the beaker, where the aluminium fused with the glass and fractured
it... the beaker was ruined, but did not shatter, it had several small cracks at the bottom though.
On another occasion, I had this erlenmeyer in a sand bath, covered with a small piece of aluminum paper. I had set the hotplate at max to rapidly
dessicate some Sr chloride... Same thing happened! The aluminum partially melted, and several sand grains fused to the bottom of the erlenmeyer along
with bits of aluminum paper. So I never used aluminum paper again.
The only use for Al paper would be to create a "heat shield" by wrapping the entire apparatus (top of hotplate/sand bath/vessel) with a loose shield
to concentrate the heat and avoid radiation loss. I do this when I react/boil something outside, because with the air currents, it takes an eternity
for a sand bath to reach optimal temperature, if ever...
Ah right. Are you talking about using coppershots instead of sand? In other words a copper BB bath? I like the idea of that a lot because it would be
less messy than using sand. Nowhere near as inert though, if hot reactant escaped the flask and landed in the copper bath, you might have to deal with
a reaction. Same goes for using Al foil balls. grndpndr - 24-9-2011 at 20:13
Pretty sure std .177 BBs are copper plated steel shot.
IIRC the cu plating is to help lubricate/buffer the air rifles mechanism and likely most important prevent rust.FWIW
