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Magpie
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[*] posted on 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. :D

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! :o 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]




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[*] posted on 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??
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[*] posted on 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?
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[*] posted on 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.
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[*] posted on 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
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[*] posted on 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.
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[*] posted on 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 :D 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]
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[*] posted on 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 :D 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.
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[*] posted on 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]




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[*] posted on 12-12-2016 at 08:44


Quote: Originally posted by brubei  
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 :D 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]




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[*] posted on 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 :D 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]




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[*] posted on 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
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[*] posted on 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).
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[*] posted on 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.
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[*] posted on 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)
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[*] posted on 13-12-2016 at 14:01


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

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]
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[*] posted on 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.




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[*] posted on 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 :D
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[*] posted on 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.
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[*] posted on 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 :D


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]




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[*] posted on 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)
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[*] posted on 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 :D

IMG_20161215_224824.jpg - 1.1MB IMG_20161215_225132.jpg - 995kB IMG_20161215_230211.jpg - 362kB

[Edited on 17-12-2016 by valekovski]
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