Sciencemadness Discussion Board

Graphite bath for heating round bottom flasks?

stainedflask - 14-7-2009 at 14:14

Hey guys. I'm a long time lurker. I think I registered briefly in the past, under who knows what name, and then some combination of being bewildered on where to begin, ADD, and general life issues took me elsewhere for awhile.

Just had my interest rekindled when I stumbled across the illustrated guide to home chemistry experiments a couple weeks ago.

For the moment, I'm largely confining myself to this book until I get a good feel for this stuff. I already had one foolish mishap on the 2nd experiment in the book. "Distilling alcohol" became "Cover workbench with hot oil". I was using an oilbath to heat the alcohol solution in a round flask. Unthinkingly, I removed a stopper to add more solution, as all the alcohol was boiled off, leaving only water. I'm sure you can guess how the oil covered the bench at that point.

Anyway, this mishap caused me to think about the hot oilbath in general, and how nasty it could be if this were something other than an alcohol solution (not that I intend on it happening the same way, mind you.. but the glass could just break someday, for all I know). I searched the board a bit and saw mention of a sandbath as a safer alternative, although it seems these can burn out the hotplate easily because of poor thermal transfer of the sand. My hotplate has a sticker on the cord saying not to use above setting 3 for a sandbath.

In searching for alternatives, I thought about powdered industrial diamond at first, but it's prohibitively expensive. Then graphite sprang to mind. What about a powdered graphite bath? Graphite has a much higher thermal conductivity than either sand or oil, I think. Unless I'm interpreting the data I could find all wrong. And it's rather cheap. I'm not sure what I did with it, but I know I have a few pounds of it somewhere around here. If I could find it, I'd give this a shot. Anyone tried anything like this?

Any glaring flaws in my plan anyone would care to point out?

not_important - 14-7-2009 at 14:21

Graphite is very messy and dirty. It's fairly light and blows about. In loose form it's not that good of a thermal conductor. However it is somewhat electrically conductive, which can cause interesting problems if it gets blown about into electrical equipment.

For lower temperatures such as distilling alcohol, consider plain water or various salt solutions, which will raise the boiling point a few degrees or more. For higher temperatures fine metal shot can be used.

DJF90 - 14-7-2009 at 14:38

I seem to remember a saturated calcium chloride solution being good to about 170*C.

JohnWW - 14-7-2009 at 14:48

As an alternative to graphite or steel or lead shot (which is rather expensive, being made for shotgun cartridges by dropping the molten metals from a height into a tank of water), you could use steel (or brass or copper) turnings from an engineering workshop. Copious quantities of such turnings are produced when castings or forgings are turned on a lathe or drilled or milled.

kclo4 - 14-7-2009 at 15:35

turnings could be hazardous, they are often covered in oil from the lathe, etc and may smoke, etc Also if it fine-ish and heated for a decent amount of time etc they may ignite, no?

How about a mixture of something?

Lambda-Eyde - 14-7-2009 at 15:42

How about a slurry of powdered graphite and silicone oil?

12AX7 - 14-7-2009 at 16:53

Just carve a hunk of graphite. One-time messiness, and a wonderful thermal conductor. Maybe line it with plaster like the regular mantles?

I wouldn't recommend swarf, even metal swarf is fairly fluffy stuff. Plus the oil and ignition problems as mentioned.

Tim

kclo4 - 14-7-2009 at 18:25

Is plaster of paris an option? It is fine, and so it may conduct better then sand, and it is fairly cheap and unreative.

[Edited on 15-7-2009 by kclo4]

stainedflask - 14-7-2009 at 19:44

Thanks a lot for the suggestions guys. I didn't think how messy it might be. Or give consideration to how easily it might invade electrical appliances. I'm glad I asked before giving it a go.

I like the plaster of paris idea, though I think I'll probably go with the saltwater suggestion for now. I'd completely forgotten about that possibility. Next time I have some plaster around, I'll give it a shot though.

Where exactly does one get large chunks of graphite, by the way? I don't think I've ever even seen it in solid pieces other than in drawing implements.

12AX7 - 14-7-2009 at 20:40

eBay. It goes pretty cheap. As a bonus, you can carve blocks for electrolysis anodes, if you're into that sort of thing.

Plaster is an excellent insulator, you'll only get away with it for thin layers.

Tim

kclo4 - 14-7-2009 at 20:57

Aluminium oxide!
.. maybe

"Aluminium oxide is an electrical insulator but has a relatively high thermal conductivity (40 Wm-1K-1) " - wiki

compare its thermal conductivity with other materials: http://en.wikipedia.org/wiki/Thermal_conductivity#List_of_th...

Also this can be found as a powder for polishing various things pretty easily, also it isn't that reactive.

Diamond powder sounds perfect though.. just look at how conductive that is! Even though they make it synthetically, its probably still pretty expensive for using it to heat a RBF, despite how cool that would be.


JohnWW - 14-7-2009 at 21:15

Quote: Originally posted by kclo4  
turnings could be hazardous, they are often covered in oil from the lathe, etc and may smoke, etc. Also if it fine-ish and heated for a decent amount of time etc they may ignite, no?
Steel (or brass or bronze) turnings cannot spontaneously ignite under ordinary laboratory temperatures used for heating round-bottomed flasks for synthetic organic chemistry purposes. If heated for a long time in the presence of plenty of moist air, they would probably oxidize on the surface, and you would eventually end up with a lot of rusty turnings, but that is all, and they would cost next to nothing to replace. BUT aluminium and especially aluminium-magnesium alloy turnings just might ignite, though.

UnintentionalChaos - 14-7-2009 at 21:28

Quote: Originally posted by JohnWW  
Quote: Originally posted by kclo4  
turnings could be hazardous, they are often covered in oil from the lathe, etc and may smoke, etc. Also if it fine-ish and heated for a decent amount of time etc they may ignite, no?
Steel (or brass or bronze) turnings cannot spontaneously ignite under ordinary laboratory temperatures used for heating round-bottomed flasks for synthetic organic chemistry purposes. If heated for a long time in the presence of plenty of moist air, they would probably oxidize on the surface, and you would eventually end up with a lot of rusty turnings, but that is all, and they would cost next to nothing to replace. BUT aluminium and especially aluminium-magnesium alloy turnings just might ignite, though.


Ideally use copper shot though. The packing and thermal conductivity would be much better.