happybabybunny - 6-11-2010 at 22:10
I have heard of using fine salt/sand as an oil bath replacement and it should work well. I have also heard mentions of placing the RBF directly on
the hotplate and covering everything with foil. What do you guys think of this method? Seems the temperature can be regulated by opening and closing
the foil shield (maybe insulation between both foil laers). Would this work for 200C+?
hissingnoise - 7-11-2010 at 04:46
Allowing an RBF to to contact a hotplate isn't a good idea because the small contact area can cause enough thermal stress to crack the vessel even if
it's borosilicate.
There should be a gap of ~4mm between hotplate and RBF!
bbartlog - 7-11-2010 at 09:05
Direct contact is bad, as hissingnoise says; and having a gap means that even if you maintain a cozy temperature inside the foil shield, the heat
transfer is going to be rather slow (air being a decent insulator and all). If you need substantial heat, you're better off putting a flat-bottomed
vessel (I use a saucepan) on the hotplate and then using oil, sand, salt or what have you. But it does depend on what you're trying to do; if you
don't need temperatures above 100C then foil shield and RBF close to the plate may well work fine. I doubt you can do stuff like distill ethylene
glycol (197C) or concentrate sulfuric acid to 90+% using such a setup, however.
entropy51 - 7-11-2010 at 09:45
There are quite a few existing threads on heating and baths. Some of them discuss the pro's and con's of different methods. A bath of water or oil is much safer than direct heating on a hotplate.
The instructions for ceramic top hotplates often say not to use with a sand bath.