Chemgineer
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High temperature stir bar.
If you have a hot plate that can reach 500 deg C where is a good place to find a suitable stir bar?
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Precipitates
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I would probably take my chances and go with something like this on aliexpress:
Magneton High Borosilicate
If it fails it's cheap.
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Jenks
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That is the maximum temperature of the surface of the hot plate. The contents of a container on UT will not get that hot, maybe 300C.
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Sulaiman
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As above but;
I can't imagine what stirrable liquid would need 500C
The highest temperatures I've used were when boiling conc. sulphuric acid.
I suggest that first you buy a cheap set of ptfe stir bars
which will be adequate for almost all common stirring requirements.
Consider high temp. stirbars when/if you have an actual need.
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Chemgineer
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Quote: Originally posted by Sulaiman  | As above but;
I can't imagine what stirrable liquid would need 500C
The highest temperatures I've used were when boiling conc. sulphuric acid.
I suggest that first you buy a cheap set of ptfe stir bars
which will be adequate for almost all common stirring requirements.
Consider high temp. stirbars when/if you have an actual need. |
Sulphuric acid is my main use case, I could use boiling chips but I think it would be allot safer with a stir bar. I think they will probably
demagnetize though,
Could maybe try and find a piece of steel encapsulated in borosilicate.
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Jenks
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That should work up to its Curie temperature of at least 770C.
Most of the references I could find give a limit of 500C for borosilicate laboratory glassware.
[Edited on 16-4-2024 by Jenks]
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Sulaiman
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The thought of a (relatively heavy) steel rod spinning around at high speed in a glass flask containing boiling sulphuric acid is not my idea of fun.
A cobalt magnet in a glass envelope looks good,
but I'd expect a lot of wear on the flask and stirbar.
I plan for my next H2SO4 distillation to use a bubbler....
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Ubya
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does it actually need to be a stir bar?
Probably not as convenient, but overhead stirrers are a thing
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Grizli7
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You can enclose a steel rod in quartz glass of sufficient thickness with a pre-calculated thermal gap. But there are several problems here:
-To melt a quartz tube you need high-temperature gas propane + oxygen is not enough. Of course, I bent quartz tubes, but it took so long;
- After soldering, you need to mechanically align the geometry, otherwise there is a risk of flight;
-The bottom of the flask should be almost perfectly flat, although at low stirrer speeds the risk of the stick flying out is minimal. You can make a
thickening in the center - this will further reduce the risk of flying out;
- Well, the main problem is that the standard stirrer has a rather weak grip. At least after my homemade one with a neodymium magnet and when I tried
to use a homemade steel stick it simply would not be held by the magnetic field. However, mixers are different.
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Jenks
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Maybe a paper clip coated in silicone? Or boiling stones or capillary sealed at the top.
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bnull
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What about silica sand? It is inert and insoluble in sulfuric acid. Or glass wool.
Quod scripsi, scripsi.
B. N. Ull
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Deathunter88
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You do not need a stirbar or boiling chips for sulfuric acid if your heating is strong enough. From experience, bumping of sulfuric acid is only an
issue if you are barely able to boil it.
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Sulaiman
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Interesting.... I can see how that may be true
but don't you get a lot of 'not-distilled' mist going up and into the condenser?
ie impurities (salts etc.) carried over
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