Sciencemadness Discussion Board

Heating bath media ranges?

Funkerman23 - 2-11-2012 at 21:11

After wandering and searching both here and around the web I am asking you of SciMad your opinions on heating bath media.
Water I know can be used up to 100C for a bath( as well as an Air bath) but what are the max safe working temps of other media? I have heard that Mineral( Paraffin) oil can be used to around 200C but what can be used for a max range of 325C assuming magnetic stirring is used? Or is there a reference somewhere ( here or elsewhere) that lists common heating bath liquids and tier max usable temps? I really appreciate any help on this and I thank you for you time.( for the records yes I have used the search engine here and have looking for a fair bit of time. BB's are a good idea but from what I gather if I try to use magnetic stirring while using them I could damage my hotplate)

Lambda-Eyde - 2-11-2012 at 21:59

Quote: Originally posted by Funkerman23  
Water I know can be used up to 100C for a bath( as well as an Air bath) but what are the max safe working temps of other media? I have heard that Mineral( Paraffin) oil can be used to around 200C but what can be used for a max range of 325C assuming magnetic stirring is used?

When you get to these temperatures you stop using liquid baths, both because of practical problems but also because you REALLY don't want to be messing with liquids at 300 degrees. Lead starts to melt around those temperatures. Have you ever handled molten lead? I have, and I'm comfortable with a casting scoop full of molten lead, but not with a molten lead heating bath with a RBF + contents in it! If you want to go higher, there's always sand baths or BBs as you already mentioned. I have seen some old orgsyn preps that use Wood's metal baths, but that would be incredibly expensive and toxic (contains lead and cadmium).

Also, buy two liters of silicone oil for your heating bath. It's a bit expensive, but it's a good investment. It's not flammable and doesn't fume. Also, it won't spoil.
Quote: Originally posted by Funkerman23  
BB's are a good idea but from what I gather if I try to use magnetic stirring while using them I could damage my hotplate)

Where did you read that? Sounds like bullshit to me. I could be wrong, though. Only problem I can see is that ferromagnetic BB's would screw up the stirring. But not damage the stirrer...?

watson.fawkes - 3-11-2012 at 05:37

Quote: Originally posted by Lambda-Eyde  
Only problem I can see is that ferromagnetic BB's would screw up the stirring. But not damage the stirrer...?
Sure. Consider putting a large block of steel on top of the stirrer, pretty much a maximum (ordinary) magnetic load. If you manage to lock the rotor in place, you'd max out the power dissipation in the drive coil of the motor, possibly overheating it. Now if the unit is properly designed for arbitrary lab conditions, it would have a current limiting circuit to prevent that condition, but there's no reason to believe that cheap equipment has such. So it's a plausible concern, but not a certainty, and wouldn't affect some stirrers at all.

Most BB's are copper- or zinc-coated steel shot, since that's the cheapest way of making them.